Tidal Forces and Moon

Newton proposed that every object with mass exerts a gravitational pull or force on every other object with mass in the universe. Well, the earth is much more (80more) massive than the moon, which is why the moon orbits us, and not we it. (If you want to get technical, we both actually orbit an imaginary point called the center of mass.) However, the moon is sufficiently massive to make the effects of its gravitational field felt on the earth.
Anyone who lives near the ocean is familiar with tides. Coastal areas experience 2 high and 2 low tides within any 24-hour period. The difference between high and low tides is variable, but, out in the open ocean, the difference is somewhat more than 3 feet. If you’ve ever lifted a large bucket of water, you know how heavy water is. Imagine the forces required to raise the level of an entire ocean 3 or more feet! What force can accomplish this?
The tidal force of gravity exerted by the moon on the earth and its oceans. The moon and the earth mutually pull on each other; the earth’s gravity keeping the moon in its orbit, the moon’s gravity causing a small deformity in the earth’s shape.
This deformity results because the moon does not pull equally on all parts of the earth. It exerts more force on parts of the earth that are closer, and less force on parts of the earth that are farther away. Just as Newton told us: Gravitational forces depend on distance. These differential or tidal forces are the cause of the earth’s slightly distorted shape—it’s ovoid rather than a perfect sphere— and they also make the oceans flow to two locations on the earth: directly below the moon, and on the opposite side. This flow causes the oceans to be deeper at these two locations, which are known as the tidal bulges. The entire Earth is pulled by the moon into a somewhat elongated—football—shape, but the oceans, being less rigid than the earth, undergo the greatest degree of deformity.
Interestingly, the side of the earth farthest from the moon at any given time also exhibits a tidal bulge. This is because the Earth experiences a stronger gravitational pull than the ocean on top of it, and the Earth is “pulled away” from the ocean on that side. As the Earth rotates beneath the slower-moving moon, the forces exerted on the water cause high and low tides to move across the face of the earth.
The tides of largest range are the spring tides, which occur at new moon, when the moon and the sun are in the same direction, and at full moon, when they are in opposite directions. The tides of smallest range are the neap tides, which occur when the sun and the moon are at 90 degrees to one another in the sky. Tides affect us every day, of course, especially if you happen to be a sailor or a fisherman. But even if you live high and dry in Kansas or Nebraska, say, tides (and the moon) still affect you. Every day, the earth is spinning a little slower on its axis because of the moon.

Impact theory of moon

The favored theory today combines elements of the daughter theory and the capture theory in something called an impact theory. Most astronomers now believe that a very large object, roughly the size of Mars, collided with the earth when it was still molten and forming. Assuming the impact was a glancing one, it is suggested that shrapnel from the earth and the remnant of the other planetesimal (a planet in an early stage of formation) were ejected and then slowly coalesced into a stable orbit that formed the moon.
This model is also popular because it can explain some unusual aspects of the earth (the “tip” of its rotational axis, perhaps) and the moon. In the impact model, it is further theorized that most of the iron core of the Mars-sized object would have been left behind on the earth, eventually to become part of the earth’s core, while the material that would coalesce into the moon acquired little of this metallic core. This model can explain why the earth and moon share similar mantles (outer layers), but apparently differ in core composition.

Captive theory of moon

A third theory suggests that the moon was formed independently and far from the earth, but was later captured by the earth’s gravitational pull when it came too close.
This theory can account for the differences in composition between the earth and the moon, but it does not explain how the earth could have gravitationally captured such a large moon. Indeed, attempts to model this scenario with computer simulations have failed. Moreover, while the theory accounts for some of the chemical differences between the earth and moon, it does not explain the many chemical similarities that also exist.

A sister theory of moon

Another theory holds that the moon formed separately near the earth from the same material that formed the earth. In effect, the earth and the moon formed as a double-planet system.
This theory seemed quite plausible until lunar rock samples were recovered, revealing that the moon differs from Earth not only in density, but in composition. If the two bodies had formed out of essentially the same stuff, why would their compositions be so different?

Daughter theory of moon

The oldest of the four theories speculates that the moon was originally part of the earth, and was somehow spun off a rapidly spinning, partially molten, newly forming planet.
Once prevalent, this theory (sometimes referred to as the fission theory) has largely been rejected, because it does not explain how the proto-Earth could have been spinning with sufficient velocity to eject the material that became the moon. Moreover, it is highly unlikely that such an ejection would have put the moon into a stable Earth orbit.

Understanding Moon Phases

Take the time to observe the moon through all of its phases. When the moon is about three or four days “old,” Mare Crisium and other vivid features—including the prominent craters Burckhardt and Geminus—become dramatically visible, assuming it’s a clear night. You can also begin to see Mare Tranquilitatis, the Sea of Tranquility.
At day seven, the moon is at its first quarter. At this time, mountains and craters are most dramatically visible. Indeed, this is the optimum night for looking at lunar features in their most deeply shadowed relief.
As the moon enters its waxing gibbous beyond first quarter phase, its full, bright light is cheerful, but so bright that it actually becomes more difficult to make out sharp details on the lunar surface. An inexpensive “moon filter” or variable polarizing filter fitted to your telescope can help increase contrast on the bright lunar surface. As the moon verges on full, we do get great views of the eastern maria, the lunar plains. Past day 14, the moon begins to wane as the sunset terminator moves slowly across the lunar landscape. At about day 22, the Apennine Mountains are clearly visible. It was these mountains that Galileo studied most intensely, attempting to judge their height by the shadows they cast.
During the late waning phase of the moon, moonrise comes later and later at night, as the moon gradually catches up with the sun in the sky. By the time the moon passes day 26, it is nothing but a thin crescent of light present in the predawn sky. The new moon follows, and as the moon overtakes the sun, the crescent reappears (on the other side of the moon at sunset), and it begins to wax again. Here are some cold, hard facts about a cold, hard place. The moon is Earth’s only natural satellite, and in fact a very large satellite for a planet as small as the earth. The planet Mercury is only slightly larger than the moon. The mean distance between the earth and moon, as it orbits our planet from west to east, is 239,900 miles (386,239 km). The moon is less than one-third the size of the earth, with a diameter of about 2,160 miles (3,476 km) at its equator. Moreover, it is much less massive and less dense than the earth—1/80 as massive, with a density of 3.34 g/cm3, in contrast to 5.52 g/cm3 for the earth. If the earth were the size of your head, the orbiting moon would be a tennis ball 30 feet away.
Because the moon is so much less massive than the earth, and about a third as big, its surface gravity is about one-sixth that of our planet. That’s why the Apollo astronauts could skip and jump like they did, even wearing those heavy space suits. If you weigh 160 pounds on the earth’s surface, you would weigh only 27 pounds on the moon. This apparent change would give you the feeling of having great strength, since your body’s muscles are accustomed to lifting and carrying six times the load that burdens them on the moon. Of course, your mass—how much matter is in you—does not change. If your mass is 60 kilograms (kg) on the earth, it will still be 60 kg on the moon. the moon is in a synchronous orbit around the earth; that is, it rotates once on its axis every 27.3 days, which is the same time that it takes to complete one orbit around the earth. Thus synchronized, we see only one side of the moon (except for the tantalizing peek at the far side that libration affords).

What You Can See On The Moon?

Even if you don’t have a telescope, there are some very interesting lunar observations you can make. Have you ever thought that the moon looks bigger when it’s closer to the horizon? It’s just an optical illusion, but you can test it out. The angular size of the moon is surprisingly small. A circular piece of paper just about 0.2 inches in diameter held at arms’ length should cover the moon. At the next full moon, cut out a little disk of that size and prove to yourself that the moon stays the same size as it rises high into the sky.
The telescope through which Galileo Galilei made his remarkable lunar observations was a brand-new and very rare instrument in 1609; but you can easily surpass the quality of his observations with even a modest amateur instrument.
Why is it so exciting to point your telescope at the moon?
Because no other celestial object is so close to us. Being so close, the moon provides the most detailed images of an extraterrestrial geography that you will ever see through your own telescope.
When should you look at the moon?
The easy answer is: anytime the sky is reasonably clear. But if you’re thinking that you should always wait until the moon is full, think again. When is the best time to view a rugged Earthly landscape at its most dramatic? When the sun is low, early in the morning or late in the afternoon, and the light rakes across the earth, so that shadows are cast long and all stands in bold relief.
The same holds true for the moon. When you can see the sunrise or sunset line (the terminator), and the moon is not so full as to be blindingly bright, that is when the topography of the moon will leap out at you most vividly. This characteristic means that you’ll get some very satisfying viewing when the moon is at one of its crescent phases, and probably not at its full phase.

What Galileo Saw on the moon?

It is possible to observe many features of the moon without a telescope. One of the first things you should try is to track its daily motion against the background stars. Since the moon travels around the earth (360 degrees) in
27.3 days, it will travel through about 13 degrees in 24 hours, or about half a degree (its diameter) every hour.
Galileo was the first person to look at the moon through a telescope; indeed, its mottled gray face was one of the first celestial objects on which he trained his new instrument in 1609.
What he saw conflicted with existing theories that the surface was glassy smooth; it was instead rough and mountainous. He closely studied the terminator, or the boundary separating day and night, and noted the shining tops of mountains. Using simple geometry, he calculated the height of some of the mountains based on the angle of the sun and the estimated length of shadows cast. Galileo overestimated the height of the lunar mountains he observed; but he did conclude rightly that their altitudes were comparable to Earthly peaks.
Noticing mountains and craters on the moon was important, because it helped Galileo conclude that the moon was fundamentally not all that different from the earth. It had mountains, valleys, and it even had what were called seas—in Latin, maria though there is no indication that Galileo or anyone else maintained after telescopic bservations that the maria were water-filled oceans. Conten-ding that the moon resembled the earth in 1609 was not a small thing. This statement implied that there was nothing supernatural or special about the moon or perhaps the planets and the stars, either. Followed to its conclusion, the observation implied that there was perhaps nothing divine or extraordinary about the earth itself. The earth was a body in space, like the moon and the other planets.

Lunar Looking

While the world greeted Jules Verne’s 1865 book De la Terre à la Lune (translated in 1873 as From the Earth to the Moon) with acclaim and wonder, it was hardly the first fictional speculation about a voyage to our nearest cosmic neighbor. The Greek satirist Lucian had written about such a flight as early as the second century C.E. and the moon, our constant companion, has always been an object of intense fascination.
Its reflected silvery glow bathes the Earth with romance and mystery. Its changing face, as it travels through its monthly cycle, has always commanded our attention, as have its peculiarly human qualities: Unlike the stars, it is pocked, mottled, imperfect. Almost all cultures at all times have seen some sort of face or figure in the features of the moon. Only rather recently have we realized just how important the moon has been in the evolution of our planet. The sun is so intensely brilliant that to gaze at it is to go blind. But the moon, coincidentally the same size in the sky as the sun, shines with harmless reflected light that invites us to gaze and gaze—to become lunatics.

What If We Had No Moon?

It seems like a reasonable question to ask. What if we had no moon? Would it matter? What has the moon done for me lately?
It turns out that the presence of such a large moon as we have is unusual for a terrestrial planet. Mercury and Venus have no moons, and Mars has two tiny moons, Phobos and Deimos. To have a moon roughly 1/3 the size of the planet is unique in the inner solar system. Our Moon, for example, is as large as some of the moons of the giant gas planets in the outer solar system. If there were no moon, we would have no ocean tides, and the rotation rate of the earth would not have slowed to its current 24 hours. It is thought that early in the life of the Earth, it rotated once every 6
hours. The moon also appears to stabilize the rotational axis of the Earth. The Moon, in periodically blocking the light from the Sun’s photosphere gives us a view of the outer layers of the Sun’s atmosphere, and it also gave early astronomers clues to the distribution of objects in the solar system.

Our Closest Neighbor : The Moon

It has been more than 30 years since Neil Armstrong stepped from the Apollo 11 Lunar Lander onto the surface of the moon. The moon is still the only celestial body other than the Earth where humans have stood. But why did we go there? Columbus had sailed to a place promising great riches to exploit. The moon, in contrast, was and is a lifeless orb, devoid of water (mostly!), air, sound, weather, trees, or grass. While Columbus’s voyages had their tight moments (he once had to “predict” a solar eclipse to impress the natives), on his return from the fourth and final voyage to the New World, Columbus announced that he had indeed found an Earthly paradise.
But the moon?
From the pictures we’ve all seen, the lunar landscape is one of rock, dust, and desolation. And although the astronauts were seen skipping across its surface, they were clearly happy to return to mother Earth. Why on earth did our nation expend such effort, treasure, and risk to send astronauts to the lunar surface? What have we

The Demise of Mir

After several years of mishaps and close calls, the decision was made to discontinue
use of the Mir Space Station and to concentrate on the collaboration with the international community on the International Space Station. Early in 2001, the Mir Space Station was de-orbited and allowed to crash into the South Pacific Ocean. At 12:55 A.M. EST on March 22, 2001 (05:55 Greenwich Mean Time), the Mir station was 50 km (31 mi) above Earth’s surface. At 12:58 A.M. EST (05:58 GMT, 8:55 A.M. Moscow time) fragments of the station hit the ocean.
Alix Bowles, Project Coordinator for MirReentry.com watched the space station break into pieces as it streaked through the sky from a beach in Fiji. “It was a stunning blue steak followed by a sonic boom,” he said. “The pieces had a blue incandescence to them. There was something very peaceful about it,” he added. In its later years, the Mir station had become the butt of late-night television jokes, but, in fact, it was a productive scientific instrument and an important test bed for technology used on the International Space Station. Mir lasted years far longer than its designers had envisioned.

Skylab

On May 14, 1973, the United States launched its first orbiting space station, Skylab, designed to accommodate teams of astronauts to conduct a variety of experiments in geography, engineering, Earth resources, and biomedicine. Such work was carried out during 1973 and the beginning of 1974. In 1974, the craft’s orbit was adjusted to an altitude believed sufficient to keep Skylab in orbit until 1983, when a visit from the Space Shuttle was contemplated. At that time, the orbit would again be adjusted. Unfortunately, Skylab wandered out of orbit prematurely, in June 1978, and ultimately disintegrated and fell into the Indian Ocean on July 11, 1979.

Space Shuttles and Space Stations

The flight of Apollo 17 in 1972 was the last manned lunar mission, but not the end of the U.S. manned space program. On April 12, 1981, the first Space Shuttle, a reusable spacecraft (the previous space capsules had been one-shot vehicles) was launched. The Shuttle was intended to transport personnel and cargo back and forth from a manned space station, planned for Earth orbit. So far, Shuttle missions have carried out a variety of experiments, have delivered satellites into orbit, and have even repaired and upgraded the Hubble Space. In 1999, it started its most ambitious mission: the construction of an international space station, to be built in conjunction with Russia, Japan, and the European Space Agency (ESA). The realities of politics and economics mean that, in the twenty-first century, countries will be much more likely to cooperate in the race to space.

A More Distant Voyager

The Cassini-Huygens mission, a joint undertaking of NASA, the European Space Agency (ESA), the Italian Space Agency (ASI), and several other organizations, was sent on its way October 15, 1997, to investigate Saturn as well as Titan (one of Saturn’s moons). Some scientists believe that Titan might support life or, at least, offer conditions in which life could develop. The mission was named Cassini, in honor of the seventeenth-century French-Italian astronomer Jean Dominique Cassini, who discovered the prominent gap in Saturn’s main rings; and Huygens, after the Dutch scientist Christiaan Huygens, who discovered the Saturn moon Titan in 1655, as well as the rings of Saturn. It recently transmitted dramatic images of Jupiter as it sped past on its way to Saturn.

Mars Observer, Surveyor, and Pathfinder

Mars Observer, launched on September 25, 1992, was to conduct extensive imaging work while orbiting Mars, but contact was lost with the spacecraft on August 22, 1993, as the satellite was establishing an orbit around the red planet. It is possible that a fuel tank exploded, destroying the spacecraft. Mars Global Surveyor was launched on November 7, 1996, and is continuing a long project of (among other things) detailed low-altitude mapping of the Martian surface. Unexpected oscillations in its solar panels while coming into a circular orbit around the planet caused the start of the major surface mapping program to be delayed by almost a year.

Although the Global Surveyor project is extraordinarily ambitious, the public may have been more excited by the mission of the Mars Pathfinder. The craft was launched on December 4, 1996, and landed on Mars the following summer, using a combination parachute and rocket-braking system, as well as an air bag system to ensure a soft, upright landing. A “micro-rover” vehicle was deployed, which began transmitting extraordinary panoramic and close-up pictures of the Martian landscape. It is little wonder that Pathfinder has caused such a stir. We’ve always been fascinated by Mars, which, of all the planets, seems most like Earth and has often been thought of as possibly harboring life—even civilization.

Magellan, Galileo, and Ulysses

More recent U.S. planetary probes have been increasingly ambitious. Magellan was launched in May 1989 and ultimately placed into orbit around Venus. Using high-resolution radar imaging, Magellan produced images of more than 90 percent of the planet, yielding more information about Venus than all other planetary missions combined.
The spacecraft made a dramatic conclusion to its four-year mission when it was commanded to plunge into the planet’s dense atmosphere on October 11, 1994, in order to gain data on the planet’s atmosphere and on the performance of the spacecraft as it descended.
On October 18, 1989, Galileo was launched on a journey to Jupiter and transmitted data on Venus, the earth’s moon, and asteroids before reaching Jupiter on July 13, 1995, and dropping an atmospheric probe, which gathered data on Jupiter’s atmosphere. After an extended analysis of the giant planet, Galileo began a mission to study Jupiter’s moons, beginning with Europa. The so-called Galilean moons were discovered by the mission’s namesake, Galileo Galilei in 1610. The Ulysses probe was delivered into orbit by the shuttle Discovery on October 6, 1990. A joint project of NASA and the European Space Agency (ESA), Ulysses gathers solar data and studies interstellar space as well as the outer regions of our own solar system. Much of the spacecraft’s instrumentation is designed to study x-rays and gamma rays of solar and cosmic origin.

Pioneers and Voyagers

In the fall of 1958, Pioneer 1 was launched into lunar orbit as a dress rehearsal for the planetary probes that followed. The rest of the Pioneer craft probed the inner solar system for planetary information, and Pioneers 10 (1972) and 11 (1973) explored Jupiter and Saturn, the giants at the far end of our solar system. Later, in 1978, Pioneer Venus 1 and Pioneer Venus 2 orbited Venus to make surveys of that planet’s lower atmosphere and, using radar imaging, penetrated thick gaseous clouds in order to reveal the spectacular and forbidding landscape below.

Mariners and Vikings

The U.S. Mariner program launched probes designed to make close approaches to Mars, Venus, and Mercury. Mariner 2 (1962) and Mariner 5 (1967) analyzed the atmosphere of Venus. Mariner 4 (1964) and 6 and 7 (both 1969) photographed the Martian surface, as well as analyzed the planet’s atmosphere. Mariners 6 and 7 also used infrared instruments to create thermal maps of the Martian surface, and, in 1971, Mariner 9, in orbit around Mars, transmitted television pictures of the planetary surface. Mariner 10, launched in 1973, was the first spacecraft to make a close approach to Mercury and photograph its surface.
But even more exciting were the two Viking missions, launched in 1975. The following year, both made successful soft landings on Mars and conducted extensive analysis of the Martian surface.

The Apollo Missions

The data from the unmanned probes and orbiters was overwhelming in its volume and detail. Some critics continued to argue: Why send human beings? The manned missions clearly captured public attention, beginning with the Soviet Vostok series (1961–1963, including Vostok 6, which carried the first woman into space, Valentina V. Tereshkova) and the U.S. Mercury series (1961–1963). The Mercury series included two suborbital flights and the first U.S. manned flight in orbit, Friendship 7, commanded by John H. Glenn Jr., and launched on February 20, 1962.

(On October 29, 1998, 77-year-old Senator John Glenn boarded the Space Shuttle Discovery and became the oldest man in space. He returned from the mission on November 7.) The U.S. Gemini program came next, twelve two-man spaceflights launched between 1964 and 1967. The Gemini flights were intended very specifically to prepare astronauts for the manned lunar missions by testing their ability to maneuver spacecraft, to develop techniques for orbital rendezvous and docking with another vehicle—essential procedures for the subsequent Apollo Moon-landing program—and to endure long spaceflights. The eight-day Gemini 5 mission, launched August 21, 1965, was the longest spaceflight to that time. The Soviets also developed larger launch vehicles and orbiters. Voskhod 1, launched on October 12, 1964, carried three “cosmonauts” (as the Russians called their astronauts) into Earth orbit.

The U.S. Apollo lunar missions not only made up the most complex space exploration program ever conceived, but were perhaps the most elaborate scientific and technological venture in the history of humankind. Today, even if we had the desire, we no longer have the launch vehicles required to bring astronauts to the moon. According to the mission plan, a Saturn V multistage booster (rocket) would lift the 3-man Apollo spacecraft on its 21/4-day voyage to the moon, leaving behind the launch stages in pieces as it left the earth. After its journey, the small remaining piece of the initially launched craft would become a satellite of the moon, and the Lunar Module, with two men aboard, would separate from the orbiting Command Module and land on the moon. After a period of exploration on the lunar surface, the astronauts would climb back into the Lunar Module, lift off, and dock with the orbiting Command Module, which would fire its rockets to leave its lunar orbit and carry the three astronauts back to Earth.

After several preliminary missions, including Earth- and Moon-orbital flights, Apollo 11 was launched on July 16, 1969. On board were Neil A. Armstrong, Edwin E. “Buzz” Aldrin Jr., and Michael Collins. While in lunar orbit, Armstrong and Aldrin entered the Lunar Module, separated from the Command Module, and landed on the Moon, July 20, 8:17 P.M. Greenwich Mean Time.

“That’s one small step for [a] man,” Armstrong declared, “one giant leap for mankind.” And perhaps that sentence expressed the rationale for the effort, which went beyond strictly scientific objectives and spoke of and to the human spirit. Not that science was neglected. During their stay of 21 hours and 36 minutes, the astronauts collected lunar soil and moon rocks and set up solar-wind

Apollo 12 landed on the Moon on November 19, but Apollo 13, launched April 11, 1970, had to be aborted because of an explosion, and the astronauts, as recounted in a recent film through their great skill, resourcefulness, and courage, barely escaped death.

Apollo 14 (launched January 31, 1971), Apollo 15 (July 26, 1971), Apollo 16 (April 16, 1972), and Apollo 17 (December 7, 1972) all made successful lunar landings. Budgetary constraints, declining public interest, and the improving capabilities of unmanned missions eventually brought an end to the Apollo missions.

Lunar Probes

There were voices raised in protest, both in the political and scientific communities. Why try to put men on the moon, when unmanned probes could tell as much or more—and accomplish the mission with far less expense and danger?
The Russians had successfully launched the first lunar probe, Luna 2, on September 12, 1959, targeting and hitting the moon with it. Luna 3, launched the following month, on October 4, 1959, made the first circumnavigation of the moon
and transmitted back to Earth civilization’s first photographs of the Moon’s mysterious far side.
Another Soviet lunar first would come on January 31, 1966, when Luna 9 made a successful lunar soft landing—as opposed to a destructive impact.
In 1961, the United States launched the first of the Ranger series of nine unmanned lunar probes, hitting the moon with Ranger 4 in 1962 and orbiting it, with Rangers 7, 8, and 9, during 1964–1965. These last three missions generated some 17,000 high-resolution photographs of the lunar surface, not only valuable as astronomy, but indispensable as a prelanding survey.
From 1966 to 1968, seven Surveyor probes made lunar landings (not all successful), took photographs, sampled the lunar soil, and performed environmental analysis. Surveyor 6 (launched on November 7, 1967) landed on the lunar surface, took photographs, then lifted off, moved eight feet, landed again, and took more photographs. It was the first successful lift-off from an extraterrestrial body. The Lunar Orbiter series, five orbital missions launched during 1966–1967, mapped much of the lunar surface in 1,950 wide-angle and high-resolution photographs. These images were used to select the five primary landing sites for the manned Apollo missions.

JFK’s Challenge

On May 5, 1961, about three weeks after the Russians put a man into a single orbit, U.S. Navy commander Alan B. Shephard was launched on a 15-minute suborbital flight into space. Americans were proud of this achievement, to be sure, but the Soviets had clearly upstaged it. Just 20 days later, on May 25, President John F. Kennedy spoke to Congress: “I believe this nation should commit itself to achieving the goal, before the decade is out, of landing a man on the moon and returning him safely to Earth. No single space project in this period will be more impressive to mankind, or more important for the long-range exploration of space, and none will be so difficult or expensive to accomplish.”

First Observatories in Space

In 1962, the United States launched its first extraterrestrial observatory, the Orbiting Solar Observatory (OSO). It was the first of a series of solar observatories, designed to gather and transmit such data as the frequency and energy of solar electromagnetic radiation in ultraviolet, x-ray, and gamma ray regions of the spectrum—all regions to which our atmosphere is partially or totally opaque.

The Early Explorers

The first space satellite the United States sent into orbit was Explorer 1, launched on January 31, 1958. While the satellite didn’t beat Sputnik 1 into space, it accomplished considerably more than the Soviet probe. Explorer 1 carried equipment that discovered the innermost of the Van Allen radiation belts, two zones of charged particles that surround the earth. By 1975, when the Explorer series of missions ended, 55 satellites had been launched, including Explorer 38 (July 4, 1968), which detected galactic radio sources, and Explorer 53 (May 7, 1975), which investigated x-ray emission inside and beyond the Milky Way.

Satellites and Probes

Astronomers and other scientists were not always enthusiastically supportive of the manned space program, many of them feeling that it stole both public attention and government funding away from more useful data-gathering missions that could be carried out much more efficiently and inexpensively by unmanned satellites and probes. There is much truth to this sentiment. However, at least in the 1960s, unmanned exploratory missions continued to have high priority, and did not really suffer from the parallel development of the manned space program.

Early Human Missions

While both the Soviet Union and the United States launched a series of artificial satellites, the major goal quickly became “putting a man in space.” This objective was less scientific than psychological and political. The Soviet communists were determined to demonstrate the superiority of their technology generally and, in particular, the might of their ballistic missiles. At the time, their rockets were more powerful than what the United States had. The Soviets were eager to demonstrate that they were capable of lofting a person (and all of the machinery necessary to support a person) into space—or a warhead onto an American city.

Just as the Soviets had been first into orbit with Sputnik, so, on April 12, 1961, they were first to put a person, Yuri Alekseyevich Gagarin, into space—and into Earth orbit, no less. The first woman, Valentina Tereshkova of the USSR followed in 1963. It took America 20 more years to achieve this landmark. Through the rest of the 1960s, the Soviets and the Americans sent cosmonauts and astronauts into orbit and even had them practice working outside of their spacecraft in what were termed “extravehicular activities” or, more familiarly, space walks.

The Battle Cry of Sputnik

Impressive as the achievements of Piccard and others were, balloons could never move beyond the frontier of space. They needed the earth’s atmosphere to loft them.
After the war, scientists in America and the Soviet Union began experimenting with
so-called sounding rockets developed from the V-2s, in part to probe (sound) the upper atmosphere. While a sounding rocket was accelerated to speeds of up to 5,000 miles per hour, it would run out of fuel by about 20 miles up.

This acceleration gave the rockets sufficient velocity to continue their ascent to about a hundred miles, after which the rocket fell to Earth. Any instrumentation it carried had to be ejected, parachuted to safety and recovered, or the information had to be transmitted to a ground station by radio before the rocket crashed. The goal of rocket science at this point was not only to reach higher altitudes, but to achieve a velocity that could launch an artificial satellite into orbit around the earth. Imagine a rock thrown into the air. The force of gravity causes it to travel in a parabola and return to the earth. If the ball were thrown at a greater and greater velocity, it would travel farther and farther until it returned to the earth. At some velocity, however, the rock would never return to the earth, but continually fall toward it (this is what the moon is doing: orbiting the earth). It was no mean trick to get a satellite going fast enough to make it orbit the earth.

A single-stage rocket, like the V-2, exhausted its fuel supply before it reached sufficient altitude and velocity to achieve orbit. It lacked the necessary thrust. To build a more powerful rocket required a return to Goddard’s idea of a “stepped” or staged rocket. A staged rocket jettisoned large parts of itself as fuel in each lower part—or stage—ran out. Thus the rocket became progressively less massive as it ascended, both by burning fuel and by discarding the empty fuel tanks.

During the early and mid-1950s, there was much talk of putting a satellite into orbit, and both the United States and the Soviets declared their intention to do so. In the Cold War atmosphere of the time, it came as a great shock to Americans when the USSR was the first to succeed, launching Sputnik I (Russian for “satellite”) into orbit on October 4, 1957. The 185-pound (83.25 kg) satellite had been lofted to an altitude of about 125 miles (201 km) and had achieved the required Earth orbital velocity of some 18,000 miles (28,980 km) an hour. The first Sputnik was a primitive device by today’s standards. It did nothing more than emit a radio beep to tell the world it was there. But it didn’t have to do more than that. The point was made, the Space Age was born, and the space race had begun.

Playing with Balloons

While the V-2 had achieved great altitude by the 1940s, scientists were still a long way from attempting a human ascent. These early rockets were intended to explode at the end of the journey. If an instrument or a human were on board, explosions were to be avoided at all costs. In fact, another technology, the balloon, would be the first to take human beings into the upper stratosphere, the frontier of space. Auguste Piccard (1884–1962), a Swiss-born Belgian physicist, built a balloon in 1930 to study cosmic rays, which the earth’s atmosphere filters out. Piccard developed revolutionary pressurized cabin designs, which supported life at high altitudes, and, in 1932, reached an altitude of 55,563 feet. The following year, balloonists in the Soviet Union used Piccard’s design to reach 60,700 feet, and an American balloonist topped that later in the year at 61,221 feet.

From Scientific Tool to Weapon and Back Again

From the early 1900s through the 1930s, peacetime governments and the scientific community showed relatively little interest in supporting such pioneers as Tsiolkovsky, Goddard, and Oberth. Unfortunately, it took war in Europe, and a desire to launch bombs onto other nations, to spur serious, practical development of rockets. The research and development took place almost exclusively in Germany.
During the late 1930s, under the militaristic regime of Adolf Hitler, two rocket weapons were created. The first, known as the V-1, was more a pilotless jet aircraft than a rocket. About 25 feet long, it carried a 2,000-pound bomb at 360 miles per hour for a distance of about 150 miles. It was a fairly crude device: When it ran out of fuel, it crashed and exploded. Out of about 8,000 launched, some 2,400 rained down on London from June 13, 1944, to March 29, 1945, with deadly effect. In contrast to the V-1, the V-2 was a genuine rocket, powered not by an air-breathing jet engine, but by a rocket engine burning a mixture of alcohol and liquid oxygen.

The V-2 had a range of about 220 miles and also delivered 2,000 pounds of high explosives to its target. From September 8, 1944, to March 27, 1945, about 1,300 V-2s were launched against Britain. Scientists of every stripe spent the years from 1939 to 1945 directing their energies toward the defeat of the enemy. Many of the techniques developed during the war (radar technology and rocket engines, to name two) would become crucial to astronomy in the decades after WWII.
During the last days of the war in Europe, as U.S. forces invaded Germany from the west and Soviet forces invaded from the east, both sides scrambled to capture V-2s and, with them, German rocket scientists, such as Wernher von Braun. Both sides saw the potential in being able to deliver bombs over long distances. These rockets and the scientists who made them were at the center of the Cold War and the Space Race—a period of competition in politics and high technology between the two superpowers that dominated the postwar world.

This Really Is Rocket Science

While spaceflight was the subject of many centuries of speculation, three men worked independently to lay its practical foundation. Konstantin Eduardovich Tsiolkovsky (1857–1935) was a lonely Russian boy, almost totally deaf, who grew up in retreat with his books. He became a provincial schoolteacher, but his consuming interest was flight, and he built a wind tunnel to test various aircraft designs. Soon he became even more fascinated by the thought of space travel, producing the first serious theoretical books on the subject during the late nineteenth and early twentieth centuries.

Another quiet, introspective boy, this one a New Englander, Robert Hutchings Goddard (1882–1945), was captivated by H. G. Wells’s science-fiction novel War of the Worlds, which he read in an 1898 serialization in the Boston Post. On October 19, 1899 (as he remembered it for the rest of his life), young Goddard climbed a cherry tree in his backyard and “imagined how wonderful it would be to make some device which had even the possibility of ascending to Mars.” From that day, the path of his life became clear to him. Goddard earned his Ph.D. in physics in 1908 from Clark University in his hometown of Worcester, Massachusetts, and, working in a very modest laboratory, he showed experimentally that thrust and propulsion can take place in a vacuum (this follows from Newton’s Laws of motion—the expelled gases pushing forward on the rocket). He also began to work out the complex mathematics of energy production versus the weight of various fuels, including liquid oxygen and liquid hydrogen. These are the fuels that would ultimately power the great rockets that lofted human beings into orbit and to the moon—and still power the launch of many rockets today. Goddard was the first scientist to develop liquid-fuel rocket motors, launching the inaugural vehicle in 1926, not from some governmental, multimillion-dollar test site, but from his Aunt Effie’s farm in Auburn, Massachusetts. Through the 1930s and 1940s, he tested increasingly larger and more powerful rockets, patenting a steering apparatus and the idea of what he termed “step rockets”—what would later be called multistage rockets—to gain greater altitude.

Goddard’s achievements were little recognized in his own time, but, in fact, he had single-handedly mapped out the basics of space-vehicle technology, including fuel pumps, self-cooling rocket motors, and other devices required for an engine designed to carry human beings, telecommunications satellites, and telescopes into orbit. Hermann Oberth (1894–1989), born in Austria, was destined for a medical career, like his father, but his medical studies were interrupted by World War I. Wounded, he studied physics and aeronautics while recovering. While he was still in the Austrian army, he performed experiments to simulate weightlessness, and designed a longrange, liquid-propellant rocket. The design greatly impressed Oberth’s commanding officer, who sent it on to the War Ministry, which summarily rejected it. After the war, University of Heidelberg faculty members likewise rejected Oberth’s dissertation concerning rocket design. Undaunted, Oberth published it himself—to great acclaim—as The Rocket into Interplanetary Space (1923). In 1929, he wrote Ways to Spaceflight, winning a prize that helped him finance the creation of his first liquidpropellant rocket, which he launched in 1931.
During World War II, Oberth became a German citizen and worked with Wernher von Braun to develop rocket weapons.

The Space Race

While countless human beings have gazed up at the sky with wonder, a few were never content just to look. They didn’t want to wait for the information to get here, they wanted to go there. In the second century C.E., the Greek satirist Lucian wrote the first account we have of a fictional trip from the earth to the moon. Doubtless, someone had thought about such a trip before Lucian, and certainly many contemplated space travel after him. It was not until the eighteenth century that people were first lofted into the air by hot-air balloons. And while the airplane made its debut in 1903, human spaceflight—in which a human ventured beyond the earth’s protective atmospheric blanket—did not come about until the 1961 flight of a Soviet cosmonaut Yuri Alekseyevich Gagarin.

Chandrasekhar and the X-Ray Revolution

Electromagnetic radiation at the highest end of the spectrum can now be studied. Since x-rays and gamma rays cannot penetrate our atmosphere, all of this work must be done by satellite. Work began in earnest in 1978 when an x-ray telescope was launched, called the High-Energy Astronomy Observatory (later, the Einstein Observatory). The R"oentgen Satellite (ROSAT) was next launched by Germany in 1990. The Chandra X-ray Observatory (named for astronomer Subrahmanyah Chandrasekhar) was launched into orbit in July 1999 and has produced unparalleled high-resolution images of the x-ray universe. The Chandra image of the Crab Nebula, home to a known pulsar, showed never before seen details of the environment of an exploded star. For recent images, go to www.chandra.harvard.edu. X-rays are detected from very high energy sources, such as the remnants of exploded stars (supernova remnants) and jets of material streaming from the centers of galaxies. Chandra is the premier x-ray instrument, doing in this region of the spectrum what the Hubble Space Telescope has done for optical observations.

In 1991, the Gamma Ray Observatory (GRO) was launched by the space shuttle. It is revealing unique views of the cosmos, especially in regions where the energies involved are very high: near black holes, at the centers of active galaxies, and near neutron stars.

New Infrared and Ultraviolet Observations

Telescopes need to be specially equipped to detect infrared radiation—the portion of the spectrum just below the red end of visible light. Infrared observatories have applications in almost all areas of astronomy, from the study of star formation, cool stars, and the center of the Milky Way, to active galaxies, and the large-scale structure of the universe. IRAS (the Infrared Astronomy Satellite) was launched in 1983 and sent images back to Earth for many years. Like all infrared detectors, though, the ones on IRAS had to be cooled to low temperatures so that their own heat did not overwhelm the weak signals that they were trying to detect. Although the satellite is still in orbit, it has long since run out of coolant, and can no longer make images. The infrared capability of the Hubble Space Telescope provided by NICMOS (Near-Infrared Camera and Multi-Object Spectograph) yielded spectacular results while in operation. The Next-Generation Space Telescope (NGST) will be optimized to operate at infrared wavelengths, and will be cooled passively (by a large solar shield).

Ultraviolet radiation, which begins in the spectrum at frequencies higher than those of visible light, is also being studied with new telescopes. Since our atmosphere blocks all but a small amount of ultraviolet radiation, ultraviolet studies must be made by high-altitude balloons, rockets, or orbital satellites. The Hubble Space Telescope, for instance, has the capability to detect ultraviolet (UV) photons as well as those with frequencies in the visible and infrared. Ultraviolet observations provide our best views of stars, and stars with surface temperatures higher than the sun’s.

What is SETI?

If you’ve seen such sci-fi movies as The Arrival, Independence Day, or Contact, you already know about an organization called SETI (Search for Extra-Terrestrial Intelligence). It is an international group of scientists and others who, for the most part, use radio telescopes to monitor the heavens in search of radio signals generated not by natural phenomena, but broadcast artificially by intelligent beings from other worlds. So far, no clearly artificial extraterrestrial radio signals have been confirmed, but SETI personnel keep searching. The SETI project got a large boost recently when Paul Allen, one of the co-founders of Microsoft, committed $12.5 million to the project. The new instrument to be built exclusively for SETI will be called the Allen Telescope Array.
If you are interested in the search for extraterrestrial intelligence, you don’t have to just read about it, you can actually participate in it. A few highly committed amateur radio astronomers have built SETI-capable radio telescopes and spend time searching for artificial signals of extraterrestrial origin. If you’re not up to making such a commitment, the SETI Institute is developing an alternative. In a project called SETI@home, a special kind of screensaver program (a program that, typically, puts up a pretty, animated picture on your PC monitor when the computer is idle) has been installed on over 1.5 million computers in 224 countries. When the computer is idle, this program will use the time to go to work analyzing data from four million different combinations of frequency bandwidth and drift rate recorded by the world’s largest radio telescope at Arecibo, Puerto Rico. With thousands of computers crunching this data, the SETI Institute believes that it can analyze data more quickly, thereby increasing the chances of ferreting out a radio signal from an intelligent source. Information on SETI@home can be found on the Net at www.seti-inst.edu.

Solar Flares and Meteor Events

Solar flares, are explosive events that occur in or near an active region on the sun’s surface. Flares can be detected with a very low frequency (VLF) receiver operating in the 20- to 100-KHz (kilohertz, or thousand hertz) band. (This is below the region of the spectrum where AM radio stations broadcast.) Such a receiver can be homemade, using plans supplied by such organizations as SARA. Solar flares can also be monitored in regular shortwave radio bands with a standard shortwave receiver. Why do solar flares create radio signals? They generate x-rays that strike a part of our atmosphere called the ionosphere, greatly enhancing the electron count in this atmospheric region. These electrons generate the noise picked up by the radio.

Amateur Radio Astronomy: No-Cost and Low-Cost Approaches

A decent optical telescope costs at least $300 to $400. For free optical astronomy, all you need are your eyes. You can also do some radio astronomy for free—if you own an FM radio or a television set. We thank Tom Crowley of Atlanta Astronomy Club for many of the following ideas. Even they are affordable, don't drop it, because it breaks easily. If that's happen then I'll send you a nice condolence letter
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Have you ever witnessed a meteor shower? The streaks of light in the night sky can be quite spectacular.
Meteors are the bright trails of ionized atmosphere behind tiny bits of cometary debris that enter the earth’s atmosphere. Most meteorites are no larger than a pea. What if we told you that there was another way to watch a meteor shower—using a radio telescope otherwise known as an FM radio?
Meteor counts by radio are about ten times more accurate than visual observation—and, as with any radio observations, you can observe during the day or through clouds. It doesn’t have to be dark or clear outside. You may want to supplement your optical meteor gazing with your radio on cloudy nights.
Recall that the earth’s atmosphere is transparent to some forms of electromagnetic radiation and opaque to others. The upper atmosphere normally reflects low-frequency AM radio signals. In contrast, the atmosphere is transparent to higher frequency FM radio waves, which, as a consequence, have a shorter range. They usually penetrate and are not reflected by the atmosphere.
But something happens when a meteorite enters the atmosphere. Each piece of debris that tears into the atmosphere (at up to 40 miles per second), heats up the air around it and creates a tiny ionized (electrically charged) vapor trail in the upper atmosphere. These columns of charged particles can reflect even higher frequency FM radio waves. This temporary condition means that previously out-of-range FM broadcasts can (for a moment) be heard. During periods of known meteoric activity, stay at the low end of the FM dial and try to find FM radio stations that are from 400 to 1,300 miles away. You might call a distant friend to get the broadcast frequency of a few stations. When a distant station fades in for a second or two, you are indirectly observing a meteor. The trail behind it has momentarily reflected a distant radio signal into your receiver. It helps if you can hook up your radio to an outdoor antenna, but if the meteor shower is fairly intense, you should detect many events even without such an antenna. You can also try tuning your TV set to the lowest unused VHF channel. Again, when a distant station, normally out of range, fades in and the signal becomes strong for a second or two, you know a meteor has entered the atmosphere. (Note that this works only with a television receiving signals from an outdoor antenna—not via cable or satellite!)
Just by tuning in your radio, you can do some meaningful radio astronomy. You can make it more interesting by recording the events on tape, or keeping a written record of the number of events you detect per hour.
But amateur radio astronomy need not be limited to listening for distant FM radio or TV stations. If you are an amateur radio operator—a ham—you already have much of the equipment required for more serious radio astronomy. If you aren’t into amateur radio, you can get started for a highly variable but modest cost. The first step to take is to log onto SARA’s World Wide Web site (www.bambi.net/sara.html) for overview information.
Essentially, amateurs can use either nonimaging or imaging radio astronomy techniques. Nonimaging techniques (which monitor radio emissions without pinpointing locations) require a simple shortwave receiver, usually modified to receive a narrow band of frequencies, and a simple antenna system. With such equipment, you can track radio emission from Jupiter, solar flares, and meteor events. Imaging techniques (which provide more detailed information on the location and nature of the signal) require a more serious commitment of resources, including a much larger dish-type antenna, more sophisticated receiving equipment, reasonably elaborate recording equipment, and (probably) a rural location removed from most sources of radio interference. For purposes of this blog, we’ll restrict ourselves to the more approachable nonimaging techniques, which are more appropriate for beginners.

You Can Do This, Too!

Building a huge radio telescope like Arecibo or the Green Bank Telescope (GBT) takes a great deal of money, and so does operating one. Even if you had the cash, your neighbors (not to mention the local zoning board), might frown on your building even a modest 30-foot-diameter dish antenna in your backyard. However, remember that radio astronomy originated with non-astronomers, and there is still plenty of room in the field for amateurs, including amateurs of modest means. You can see the sky just like an ancient Aztec
astronomer. A small but committed group of enthusiasts have formed the Society of Amateur Radio Astronomers (SARA). Most books for budding astronomers don’t discuss amateur radio astronomy, though it is a fascinating and rewarding subject.

What Radio Astronomers “See”

Insomnia is a valuable affliction for optical astronomers, who need to make good use of the hours of darkness when the sun is on the other side of the earth. But as Karl Jansky discovered so many years ago, the sun is not a particularly bright radio source. In consequence, radio astronomers (and radio telescopes) can work night and day.
The VLA, for example, gathers data (or runs tests) 24 hours a day, 363 days a year. Not only is darkness not required, but you can even make radio observations through a cloud-filled sky. The senior author of this book even observed a distant star-forming region in the midst of a storm during which lightning struck near the VLA and disabled it for a few minutes.
As the Dutch astronomer Jan Oort realized after reading Reber’s work in the 1940s, radio waves opened new vistas into the Milky Way and beyond. Radio astronomers can observe objects whose visible light doesn’t reach the earth because of obscuration by interstellar dust or simply because they emit little or no visible light. The fantastic objects known as quasars, pulsars, and the regions around black holes—all of which we will encounter later in this book—are often faint or invisible optically, but do emit radio waves.
The spiral form of our own Galaxy was first mapped using the 21 cm radio spectral line from neutral (cold) hydrogen atoms, and the discovery of complex molecules between the stars was made at radio frequencies.
The very center of our own Milky Way Galaxy is hidden from optical probing, so that most of what we know of our galactic center has come from infrared and radio observation. Since radio interferometers are detecting an interference pattern, radio data has to be processed in ways different from optical data. But the end result is either a radio image, showing the brightness of the source on the sky, or a radio spectrum, showing a spectral line or lines.

Interference Can Be a Good Thing

There is a way to overcome the low angular resolution due to the size of radio waves:
link together a lot of smaller telescopes so they act like one giant telescope. A radio interferometer is a combination of two or more radio telescopes linked together electronically to form a kind of virtual dish, an array of antennas that acts like one gigantic antenna. It is as if we had small pieces of a very large optical telescope (imagine a giant mirror with a lot of its surface area punched out), so that while an interferometer has the resolution of a very large telescope, it does not have the surface area or sensitivity to faint sources of a truly gigantic telescope.
The National Radio Astronomy Observatory (NRAO) maintains and operates the Very Large Array (VLA) interferometer on a vast plain near Socorro, New Mexico, consisting of 27 large dishes arrayed on railroad tracks in a Y-shaped pattern. Each arm is 12.4 miles (20 km) long, and the largest distance between 2 of the antennas is 21.7 miles (35 km). As a result, the VLA has the resolving power of a radio telescope 21.7 miles across. The VLA recently celebrated its twentieth anniversary.
For radio astronomers who want something even larger than “very large,” there is Very Long Baseline Interferometry (VLBI), which can link radio telescopes in different parts of the world to achieve incredible angular resolutions better than a thousandth of an arcsecond (.001”). From its offices in Socorro, New Mexico, the NRAO also operates the VLBA (Very Long Baseline Array), which consists of 10 radio dishes scattered over the United States, from Mauna Kea, Hawaii, to St. Croix, U.S. Virgin Islands. In 1996, Japanese astronomers launched into Earth’s orbit a radio telescope to be used in conjunction with the ground based telescopes in order to achieve the resolution of a telescope larger than the earth itself.

Bigger Is Better: The Green Bank Telescope

In the case of radio telescopes, size really does matter. The resolution of a telescope depends not only on its diameter, but the wavelength of the detected radiation (the ratio of wavelength to telescope diameter determines the resolution). Radio waves are big (on the order of centimeters or meters), and the telescopes that detect them are correspondingly huge. Also, the radio signals that these instruments detect are very faint, and just as bigger optical telescope mirrors collect more light than smaller ones, bigger radio telescopes collect more radio waves and image fainter radio signals than smaller ones.
Collecting radio signals is just part of the task, however. You may recall that, for practical purposes, very good optical telescopes located on the earth’s surface can resolve celestial objects to 1” (1 arcsecond—1 /60 of 1 arcminute, which, in turn, is 1 /60 of 1 degree). The best angular resolution that a very large single-dish radio telescope can achieve is about 10 times coarser than this, about 10”, and this, coarse as it is, is possible only with the very largest single dish radio telescopes in the world. The National Radio Astronomy Observatory has just commissioned the world’s largest fully steerable radio telescope. The 100 m dish will have a best resolution of 14”.
The world’s largest nonsteerable single-dish radio telescope was built in 1963 at Arecibo, Puerto Rico, and has a dish, 300 meters (984 feet) in diameter sunk into a natural valley. While its great size makes this the most sensitive radio telescope, the primary surface is nonsteerable—totally immobile—and, therefore, is limited to observing objects that happen to pass roughly overhead (within 20 degrees of zenith) as the earth rotates.

Anatomy of a Radio Telescope

The basic anatomy of a radio telescope hasn’t changed all that much from Reber’s dish—though the instruments have become much larger and the electronics more sophisticated. A radio telescope works just like an optical telescope. It is just a “bucket” that collects radio frequency waves, and focuses them on a detector. A large metal dish—like a giant TV satellite dish—is supported on a moveable mount (either equatorial or altazimuth). A detector, called a receiver horn, is mounted on legs above the dish (prime focus) or below the surface of the dish (Cassegrain focus). The telescope is pointed toward the radio source, and its huge dish collects the radio waves and focuses them on the receiver, which amplifies the signal and sends it to a computer. Since the radio spectrum is so broad, astronomers have to decide which portion of the radio spectrum they will observe. Different receivers are used for observations at different frequencies. Receivers are either swapped in and out, or (more typically) the radio signal is directed to the correct receiver by moving a secondary reflecting surface (like the secondary mirror in an optical telescope).

A Telephone Man Tunes In

The first true radio astronomer was not trained as an astronomer at all. Even to this day, many astronomers who work in the radio regime were trained as physicists and electrical engineers, and later learned to apply their knowledge to astronomy. Karl Jansky, the son of a Czech immigrant who settled in Oklahoma (where Karl was born in 1905), took a degree in physics at the University of Wisconsin. After graduating, Karl went to work in 1928 not as an astronomer, but as a telephone engineer with Bell Labs. The phone company was looking for ways to make telephone communications possible with shortwave radio, but the transmissions were bedeviled by all sorts of interference.
Now most people hadn’t given much thought to radio static. After all, static was something to be avoided if possible—meaningless noise that only interfered with communications. Jansky was given the assignment of studying sources of static at a wavelength of 14.6 m in an effort to track down the precise sources of radio interference and eliminate them.
On a farm in Holmdel, New Jersey, not far from Bell Labs, Jansky set up a very ungainly looking device, which he called a merry-go-round. It was a large directional antenna, which looked rather like the biplane wing of the Wright brothers’ first airplane. It was mounted on some discarded Model T Ford wheels and could be rotated through 360 degrees by means of a motor. Using this contraption, Jansky was soon able to identify all the known sources of radio interference except one. Jansky tracked the stubborn and mysterious interference. When amplified and sent to a speaker, the interference sounded like a faint hiss. The source seemed to be in the sky, since Jansky could track it rising and setting with the stars. But it wasn’t coming from just anywhere in the sky. By the spring of 1932, Jansky traced the primary source of radio noise to the direction of the constellation Sagittarius, which astronomers Harlow Shapley and Jan H. Oort had identified (from the distribution of globular clusters in the Galaxy) as the direction of the center of the Milky Way Galaxy. Using his merry-go-round antenna, Jansky had “discovered” the center of the much bigger merry-go-round that is our galaxy. There were other sources of radio noise in the sky as well, but Jansky noted that the sun itself was not an impressive source of radio noise. This observation was a bit surprising, since the sun is so close to us. He concluded that whatever the source of radio noise, it probably wasn’t distant stars.
Jansky published his “discovery” late in 1932, and the detection of radio signals from space appeared in national newspapers by the following year. Strangely enough, Jansky himself didn’t pursue the science he had accidentally created. As for most professional astronomers, they continued to look through only one of their two windows, the portion of the spectrum available to optical telescopes. It took another nonastronomer, Grote Reber, to appreciate the possibilities of what Jansky had discovered. In today’s image-conscious world, we might call Reber a nerd. But as the example of Bill Gates has shown us, some nerds go on to change the world. Born in Wheaton, Illinois in 1911, he grew up tinkering with radio transmitters, building one powerful enough to communicate with other ham radio operators all over the world. Like many early radio astronomers, he became an electrical engineer, but never lost his interest in amateur radio, and when he read about Jansky’s discovery, he tried, without success at first, to adapt his own shortwave receiver to pick up interstellar radio waves with wavelengths of 10 cm.
He tinkered with the electronics (trying longer wavelengths), and, in 1937, built a paraboloidal antenna 30 feet in diameter. With this, Reber not only confirmed Jansky’s discovery of radio waves from the direction of Sagittarius, but found other sources in the direction of the constellations Cygnus, Cassiopeia, and elsewhere.
Reber confirmed that the radio signals did not coincide with the positions of visible stars. Directing his dish toward such bright stars as Sirius, Vega, or Rigel, he detected nothing. But looking toward a starless area in Cassiopeia, he picked up strong radio waves. He had unknowingly detected a supernova remnant known as Cassiopeia A.

Dark Doesn’t Mean You Can’t See

On a clear night far from urban light pollution, the sky is indeed dazzling. Just remember that the electromagnetic information your eyes are taking in, wondrous as it is, comes from a very thin slice of the entire spectrum. As we mentioned in the last chapter, the earth’s atmosphere screens out much of the electromagnetic radiation that comes from space. It allows only visible light and a bit of infrared and ultraviolet radiation to pass through a so-called optical window and a broad portion of the radio spectrum to pass through a radio window.
Two windows.
If your house had two windows, would you look through only one?

Seeing in the Dark

“What’s an astronomer, Daddy?”
Spending much time around a little boy or girl can be pretty exhausting. All those questions! At least this one has a quick answer: “An astronomer is a person who looks at the sky through a telescope.”
“But, Daddy, the visible spectrum is squeezed between 400 and 700 nm. What about the rest of the electromagnetic spectrum?”
Smart kid.
Until well into the twentieth century, astronomers had no way to “see” most of the nonvisible electromagnetic radiation that reached Earth from the universe. Then along came radio astronomy, which got its accidental start in 1931–1932 and was cranking into high gear by the end of the 1950s. Over the past 40 years or so, much of our current knowledge of the universe has come about through radio observations. Radio astronomy is simply the study of the universe at radio wavelengths. Astronomers used to categorize themselves by the wavelength of the observations that they made: radio astronomer versus optical astronomer. Increasingly, though, astronomers define their work more by what they study (pulsars, star formation, galactic evolution) than by what wavelength they use. The reason for this change is that, in recent years, new instruments have opened the electromagnetic spectrum to an unprecedented degree. Astronomers now have the ability to ask questions that can be answered with observations at many different wavelengths.

Read Any Good Spectral Lines Lately?

Using the spectrum and armed with the proper instrumentation, then, astronomers can accurately read the temperature of even very distant objects in space. And even without sophisticated equipment, you can startle your friends by letting them know that Betelgeuse (a reddish star) must have a lower surface temperature than the yellow sun.
Astronomers also use the spectrum to learn even more about distant sources. A spectroscope passes incoming light through a narrow slit and prism, splitting the light into its component colors. Certain processes in atoms and molecules give rise to emission at very particular wavelengths. Using such a device, astronomers can view these individual spectral lines and glean even more information about conditions at the source of the light. While ordinary white light simply breaks down into a continuous spectrum—the entire rainbow of hues, from red to violet, shading into one another—light emitted by certain substances produces an emission spectrum with discrete emission lines, which are, in effect, the fingerprint of the substance.

Hydrogen, for example, has four clearly visible spectral lines in the visible part of the spectrum (red, blue-green, violet, and deep violet). The color from these four lines (added together as light) is pinkish. These four spectral lines result from the electron that is bound to the proton in a hydrogen atom jumping between particular energy levels. There are many other spectral lines being emitted; it just so happens that only four of them are in the visible part of the spectrum. Hot hydrogen gas is the source of the pinkish emission from regions around young stars like the Orion.

In our hydrogen atom example, a negative electron is bound to a positive proton. The electron, while bound to the proton, can only exist in certain specific states or energy levels. Think of these energy levels as rungs on a ladder. The electron is either on the first rung or the second rung. It can’t be in between. When the electron moves from one energy level to another (say, from a higher one to a lower one), it gives off energy in the form of a photon. Since the levels that the electron can inhabit are limited, only photons of a few specific frequencies are given off. These particular photons are apparent as bright regions in the spectrum of hydrogen: the element’s spectral emission lines.

The Black-Body Spectrum

As Maxwell first described in the nineteenth century, all objects emit radiation at all times because the charged atomic particles of which they are made are constantly in random motion. As these particles move, they generate electromagnetic waves. Heat an object, and its atomic particles will move more rapidly, thereby emitting more radiation. Cool an object, and the particles will slow down, emitting proportionately less electromagnetic radiation. If we can study the spectrum (that is, the intensity of light from a variety of wavelengths) of the electromagnetic radiation emitted by an object, we can understand a lot about the source. One of the most important quantities we can determine is its temperature. Fortunately, we don’t need to stick a thermometer in a star to see how hot it is. All we have to do is look at its light carefully. But how?
All objects emit radiation, but no natural object emits all of its radiation at a single frequency. Typically, the radiation is spread out over a range of frequencies. If we can determine how the intensity (amount or strength) of the radiation emitted by an object is distributed across the spectrum, we can learn a great deal about the object’s properties, including its temperature.
Physicists often refer to a black body, an imaginary object that absorbs all radiation falling upon it and re-emits all the radiation that it absorbs. The way in
which this re-emitted energy is distributed across the range of the spectrum is drawn as a black-body curve. Now, no object in the physical world absorbs and radiates in this ideal fashion, but the black-body curve can be used as a reference index against which the peak intensity of radiation from real objects can be measured. The reason is that the peak of the blackbody curve shifts toward higher frequencies (and shorter wavelengths) as an object’s temperature increases.
Thus, an object or region that is emitting very short wavelength gamma ray photons must be much hotter than one producing longer wavelength radio waves. If we can determine the wavelengths of the peak of an object’s electromagnetic radiation emissions, we can determine its temperature.
Astronomers measure peak intensity with sophisticated scientific instruments, but we all do this intuitively almost every day. You have an electric kitchen range, let’s say. The knob for one of the heating elements is turned to off. The heating element is black in color. This tells you that it may be safe to touch it.
But if you were to turn on the element, and hold your hand above it, you would feel heat rising, and would know that it was starting to get hot. If you had infrared vision, you would see the element “glowing” in the infrared. As the element grows hotter, it will eventually glow red, and you would know that it was absolutely a bad idea to touch it (regardless of where the control knob happened to be pointing). At room temperature, the metal of the heating element is black, but as it heats up, it changes color: from dull red to bright red. If you had a very high-voltage electric range and a sufficiently durable heating element, you could crank up the temperature so that it became even hotter. It would emit most of its electromagnetic radiation at progressively higher frequencies.
Now, an object that omits most of its radiation at optical frequencies would be very hot. And a range will never (we hope) reach temperatures of 6000 K, like the sun. The red color you see from the range is in the “tail” of its black-body spectrum. Even when hot, it is still emitting most of its radiation in the infrared part of the spectrum.

Atmospheric Ceilings and Skylights

The information—the news—we get from space is censored by the several layers of Earth’s atmosphere. In effect, our Earth is surrounded by a ceiling pierced by two skylights. A rather broad range of radio waves readily penetrates our atmosphere, as does a portion of infrared and most visible light, in addition to a small portion of ultraviolet. Astronomers speak of the atmosphere’s radio window and optical window, which allow passage of electromagnetic radiation of these types. To the rest of the spectrum—lower-frequency radio waves, some lower-frequency infrared, and, fortunately for us, most of the energetic ultraviolet rays, x-rays, and gamma rays—the atmosphere is opaque, an impenetrable ceiling.
In many ways, the partial opacity of our atmosphere is a very good thing, since it protects us from x-ray and gamma radiation. An atmosphere opaque to these wavelengths, but transparent to visible light and some infrared, is a big reason why life can survive at all on Earth.
For astronomers, however, there is a downside to the selective opacity of the earth’s atmosphere. Observations of ultraviolet, x-ray, and gamma ray radiation cannot be made from the surface of the earth, but must be made by means of satellites, which are placed in orbit well above the atmosphere. No wonder that the advent of the space age has led to such an explosion in the amount of information that we have about the universe.

Full Spectrum

Often, when people get excited, they run around, jump up and down, and shout without making a whole lot of sense. But when atomic particles get excited, they can produce energy that is radiated at a variety of wavelengths. In contrast to the babble of an excited human throng, this electromagnetic radiation can tell you a lot, if you have the instruments to interpret it.
Our eyes, one such instrument, can interpret electromagnetic radiation in the 400 to 700 nanometer (or 4000 to 7000 Angstrom) wavelength range. A nanometer (abbreviated nm) is one billionth of a meter, or 10–9 meter. An Angstrom (abbreviated A) is 10 times smaller, or 10–10 meter. But that is only a small part of the spectrum. What about the rest of the “keyboard”?

Big News from Little Places

The Greek philosopher Democritus (ca. 460–ca. 370 B.C.E.) was partially right: matter does consist of atoms. But he would have been fascinated to know that the story doesn’t end there. Atoms can be further broken down into electrons, protons, and neutrons, and the latter two are made of even smaller things called quarks.
Electrons carry a negative electric charge, and protons a positive charge. Neutrons have a mass almost equal to a proton, but as their name implies, neutrons are neutral, with no positive or negative charge. Charged particles (like protons and electrons) that are not moving are surrounded by what we call an electric field; those in motion produce electromagnetic radiation.
James Clerk Maxwell (1831–1879) first explored what would happen if such a charged particle were to oscillate, or move quickly back and forth. He showed that a moving charged particle created a disturbance that traveled through space—without the need for any medium. Particles in space are getting banged around all the time. Atoms collide, electrons are accelerated by magnetic fields, and each time they move, they pull their fields along with them, sending “electromagnetic” ripples out into space.
In short, information about the particle’s motion is transmitted through space by a changing electric and magnetic field. But a field is not a substance. It is a way in which forces can be transmitted over great distances without any physical connection between the two places. The force of gravity, which we have discussed, can also be thought of as a field.
Let’s turn to a specific example: A star is made up of innumerable atoms, most of
which at unimaginably hot stellar temperatures are broken into innumerable charged
particles. A star produces a great deal of energy (by nuclear fusion. This energy causes particles to be in constant motion. In motion, the charged particles are the center points of electromagnetic waves (disturbances in the electromagnetic field) that move off in all directions. A small fraction of these waves reaches the surface of the earth, where they encounter other charged particles. Protons and electrons in our eyes, for instance, oscillate in response to the fluctuations in the electric field. As a result, we perceive light: an image of the star. If we happened to have, say, the right kind of infrared-detecting equipment with us, electrons if that equipment would respond to a different wavelength of vibrations originating from the same star.
Similarly, if we were equipped with sufficiently sensitive radio equipment, we might pick up a response to yet another set of proton and electron vibrations.
Remember, it is not that the star’s electrons and protons have traveled to Earth, but that the wave they generated so far away have excited other electrons and protons here. Call it an interstellar handshake.

New Wave

If you don’t happen to like math, don’t panic. Just visualize stone-generated waves rippling across a pond, and you’ll understand the basic concept of waves. But wait a minute. There is something wrong with our ripples in a pond as a model of electromagnetic radiation.
Water is a medium, a substance, something through which waves are transmitted. Space, we have said, is very nearly a vacuum, nothing. How, then, do waves move through it?
This is a question that vexed physicists for centuries. They understood the concept of waves. But they also understood that sound, a wave, could not travel through a vacuum, whereas light, also a wave, could.
Why?
At first, most scientists believed that the very fact that light is transmitted through space means that space must not be empty. They knew it didn’t have air, as on Earth, but they suggested it was filled with another substance, which they called the ether. But this fictitious substance did not long vex physicists. A series of experiments in the late nineteenth century made it clear that ether didn’t exist and that although light could be studied as a wave, it was a different kind of wave than, say, sound.

Black Hole's Secrets Revealed

Many galaxies have super-massive black holes at their core, which expel powerful jets of particles at nearly the speed of light. Using the National Radio Astronomy Observatory's very long baseline array, scientists recently confirmed the leading theory, according to which the particles are accelerated by tightly-twisted magnetic fields close to the black hole.

Just how the powerful particle jets are emitted from black holes was one of the big mysteries of astrophysics. The confirmation of the leading theory, according to which the particles are accelerated by magnetic fields, required an elusive close-up view of the particle jet's inner throat. Astronomers managed to observe the material winding in a corkscrew outward path thanks to the high resolution of the National Radio Astronomy Observatory's very long baseline array (VLBA), an observation that supports the magnetic field theory.

The international team studied a galaxy named BL Lacertae (BL Lac), situated some 950 million light-years away from Earth. BL Lac is a blazar, the most energetic type of black-hole-powered galactic core. Super-massive black holes in galaxies' cores power jets of particles and intense radiation in similar objects, including quasars and seyfert galaxies. The scientists chose to focus on the BL Lacertae Galaxy because of the high rate in which the phenomena occur in that region.

According to the theory, the phenomena occur in stages. When material is pulled inward towards the black hole, it forms a flattened, rotating disk, called an accretion disk. As the material moves from the outer edge of the disk inward, magnetic field lines perpendicular to the disk are twisted, forming a tightly-coiled bundle. Astronomers believe that this 'bundle' propels and confines the ejected particles. Closer to the black hole, space itself, including the magnetic fields, is twisted by the strong gravitational pull and rotation of the black hole, causing the emission of the particles.

Theorists have several predictions concerning material and light in these situations. The first speculation is that material moving outward in this close-in acceleration region will follow a corkscrew-shaped path inside the bundle of twisted magnetic fields. The second prediction is that light and other radiation emitted by the moving material will brighten when its rotating path is aimed most directly towards Earth.

When the team observed an outburst from BL Lac, Alan Marscher of Boston University, who led the team, said that: "That behavior is exactly what we saw." During the numerous observations, the astronomers noticed that as the material sped out from the neighborhood of the black hole, the VLBA could pinpoint its location. Other telescopes measured the properties of the radiation emitted from the knot. It appears that the theories are very precise: bright bursts of light, X-rays, and gamma rays occurred when the knot was at the exact locations predicted by the theories. In addition, the alignment of the radio and light waves (a property called polarization) rotated as the knot wound its corkscrew path inside the tight throat of twisted magnetic fields. According to Marscher, this observation gave the researchers an unprecedented view of the inner portion of one of these jets, and therefore, they gained information critical to the understanding of how these particle accelerators work.

Obviously, the researchers were excited about the new discovery. "We have gotten the clearest look yet at the innermost portion of the jet, where the particles actually are accelerated, and everything we see supports the idea that twisted, coiled magnetic fields are propelling the material outward," Marscher said. It is evident that this is a major advance in the understanding of a remarkable process which occurs throughout the Universe.

TFOT has reported on images of the Triangulum Galaxy, which were captured during over 11 hours of exposure time, and on the discovery of the building blocks of life in space, made using NASA's Spitzer Space Telescope. Other related TFOT stories are the detection of the largest known comet outburst and a new explanation of the way the Peruvian Meteorite made it to Earth, given by an expert in extraterrestrial impacts from Brown University.

Electronic Radiation as Waves

We can understand how electromagnetic radiation is transmitted through space if we appreciate that it involves waves. What is a wave? The first image that probably jumps to mind is that of ocean waves. And ocean waves do have some aspects in common with the kind of waves that we use to describe electromagnetic radiation. One way to think of a wave is that it is a way for energy to be transmitted from one place to another without any physical matter being moved from place to place. Or you may think of a wave as a disturbance that carries energy and that occurs in a distinctive and repeating pattern. A row boat out in the ocean will move up and down in a regular way as waves pass it. The waves do transmit energy to the shore (think of beach erosion), but the row boat will stay put.
That regular up-and-down motion that the rowboat experiences is called harmonic motion. But there are two important differences with electromagnetic radiation: The sources of waves are things on atomic scales (electrons and the nuclei of atoms), and no medium is required for electromagnetic waves to travel through space. The “pond” of space consists only of electric and magnetic fields, and photons of light are ripples in that ghostly pond.
Waves come in various shapes, but they all have a common anatomy. They have crests and troughs, which are, respectively, the high points above and low points below the level of an undisturbed state (for example, calm water). The distance from crest to crest (or trough to trough) is called the wavelength of the wave. The height of the wave—that is, the distance from the level of the undisturbed state to the crest of the wave—is its amplitude. The amount of time it takes for a wave to repeat itself at any point in space is its period.
In other words, the period is the time between the passage of wave crests as seen by an observer in the bobbing row boat. The number of wave crests that pass a given point during a given unit of time is called the frequency of the wave. If many crests pass a point in a short period of time, we have a high-frequency wave. If few pass that point in the same amount of time, we have a low-frequencywave. The frequency and wavelength of a wave are inversely proportional to one another, meaning that as one gets bigger, the other gets smaller. High frequency radiation has short wavelengths.

Understanding Facts about Electromagnetic Radiation

Electromagnetic radiation sounds like dangerous stuff—and, in fact, some of it is. But that the word radiation need not set off sirens in your head. It just describes any way energy is transmitted from one place to another without the need for a physical connection between the two places. We use it as a general term to describe any form of light. It is important that radiation can travel without any physical connection, because space is essentially a vacuum; that is, much of it is empty. If you went on a space walk clicking a pair of castanets, no one, including you, would hear your little concert. Sound is transmitted in waves, but not as radiation. Sound waves require some medium to travel in. So despite what most science fiction movies would lead you to believe, explosions in space are silent. Light (and other forms of electromagnetic radiation) requires no such medium to travel, although many physicists tried in vain to detect a medium, which they called the ether. We’ll talk more about this fact in a moment.
The electromagnetic part of the phrase denotes the fact that the energy is conveyed in the form of fluctuating electric and magnetic fields. These fields require no medium to support or sustain them.

Young galaxies are a star-packed puzzle

These images taken by NASA's Hubble Space Telescope show nine compact, ultradense galaxies as they appeared 11 billion years ago.

By SPACE.com Staff
Several newfound galaxies seen as they existed when the universe was young are packed with improbable numbers of stars.

Astronomers don't know what's going on.

The nine galaxies are 11 billion light-years away, which means the light astronomers are looking at left the galaxies 11 billion years ago, when the universe was less than 3 billion years old.

Each of the newly studied galaxies weighs about 200 billion times the mass of the sun yet is a mere 5,000 light-years across. Our Milky Way Galaxy is a fraction of that heft at roughly 3 million times the sun's mass, and yet it stretches across 100,000 light-years of space.

The compact galaxies have been furiously forming stars; each contains as many stars as a typical large galaxy of today, the new observations reveal.

"Seeing the compact sizes of these galaxies is a puzzle," said Pieter G. van Dokkum of Yale University, who led the study. "No massive galaxy at this distance has ever been observed to be so compact."

Since no modern galaxies — galaxies in the nearby universe — are so compact, the scientists assume compact galaxies from the early universe must have gotten much larger as they matured beyond the snapshots of ancient time now being studied. But nobody knows how.

"They would have to change a lot over 11 billion years, growing five times bigger," van Dokkum said. "They could get larger by colliding with other galaxies, but such collisions may not be the complete answer."

Astronomers used NASA's Hubble Space Telescope and the W.M. Keck Observatory on Mauna Kea, Hawaii to make the new observations, which were announced today and were detailed in the April 10 issue of the Astrophysical Journal Letters.

Van Dokkum and his colleagues had previously studied the galaxies in 2006 with the Gemini South Telescope to determine their distances, and showed that the stars are a half a billion to a billion years old. The most massive stars had already exploded as supernovae.

One reason these galaxies were so dense, van Dokkum suggested, involves the interaction of dark matter and hydrogen gas in the nascent universe. Dark matter is an invisible form of matter that accounts for most of the universe's mass. Shortly after the theoretical Big Bang, the universe contained an uneven landscape of dark matter. Hydrogen gas became trapped in puddles of the invisible material, the thinking goes, and began spinning rapidly in dark matter's gravitational whirlpool, forming stars at a furious rate.

Based on the galaxies' mass, the astronomers estimated that the stars are spinning around their galactic disks at roughly 890,000 to 1 million mph (400 to 500 kilometers a second). Stars in today's galaxies, by contrast, are traveling at about half that speed because the setups are larger and rotate more slowly.

Copyright 2007, SPACE.com Inc. ALL RIGHTS RESERVED.

About Light

The light we receive from distant sources is generated on the tiniest of scales. To explore the largest objects, such as galaxies, we have to first understand the smallest of objects, atoms and the particles making up atoms. The photons that we detect with our eyes and catch with our telescopes were generated in many different ways: sometimes by electrons hopping between different orbital levels in an atom, or other times by the energetic collisions of atomic nuclei. We now explore the ways in which photons of light arise, how they get from there to here, and what they can tell us about the objects that we observe.
We have concentrated thus far on optical photons (the ones that we can see with our eyes). As it turns out, our eyes respond to “visible” wavelengths because that is where the peak of the emission from the sun is located in the electromagnetic spectrum. If our eyes were most sensitive to infrared radiation, for example, we would see some things we can’t now see (body heat), but would miss a lot of other useful stuff. In this chapter, we’re going to talk more about visible light and the electromagnetic spectrum, of which visible light is a tiny subset. Think of it this way: If the electromagnetic spectrum is represented by a piano keyboard, then the visible part of the spectrum is but a single key or note. In the cosmic symphony, there are many notes, and we want to be able to hear them all. If you’re concerned that this sounds more like physics than astronomy, you’re right. But don’t be intimidated. Most of astronomy involves applications of physics principles, and we are convinced that understanding what you are seeing when you look at a star greatly enhances the experience of looking. Remember this astounding fact : When you look at the light from our sun or a distant star, you are witnessing the product of nuclear fusion reactions that are, every second, releasing more energy than any atomic explosion Earth has ever witnessed. Yet it is not just brute energy, but also information from the sky. Let’s take a closer look.

Don’t Look Too Hard

Next, relax. Don’t look too hard. We mean this as sincere and literal advice. Your eye’s sharpest color vision is in the center of your field of view. This is where color-receptor neurons known as cones are most densely concentrated. However, so-called rods, the visual receptors sensitive to black, white, and shades of gray, while insensitive to color, are more sensitive than cones to low levels of light. This means you can actually better see fainter objects with your peripheral vision than with your center-field vision. Learn to look askance at the stars. This practice is sometimes called “averted vision.” Using it, you will typically see fainter stars.
Peering through a telescope for extended periods is fun, but it can also be fatiguing. Don’t squint. Don’t peer. Step away from your telescope periodically to walk around. Relax and enjoy.
You’ll enjoy your astronomy sessions more, as well as reduce fatigue, if you practice keeping both eyes open when you look through the eyepiece. If you can’t resist the urge to close one eye, buy a pirate’s eye patch from the local toy store or costume shop. Then you can keep both eyes open without distraction and even feel like a real celestial navigator. A parrot on the shoulder is optional.

Hubble telescope captures crashing galaxies

WASHINGTON (Reuters) - Images of colliding galaxies show them spinning, sliding and slipping into one another, wreaking stellar destruction that will give birth to new and larger galaxies.

The Maryland-based Space Telescope Science Institute released 59 new images from the Hubble Space Telescope on Thursday to celebrate the 18th anniversary of its launch.

"This new Hubble atlas dramatically illustrates how galaxy collisions produce a remarkable variety of intricate structures in never-before-seen detail," the Institute said in a statement.

"Astronomers observe only one out of a million galaxies in the nearby universe in the act of colliding. However, galaxy mergers were much more common long ago when they were closer together, because the expanding universe was smaller."

The color images, available online, are a look back in time. It takes hundreds of millions of years for galaxies to merge and the light from their stars has traveled for hundreds of millions of years across space.

Because it orbits outside the Earth's atmosphere, Hubble's cameras can take extremely sharp images.

Its future was controversial, as it requires regular servicing by space shuttle astronauts to stay in working condition.

After the 2003 Columbia space shuttle disaster, a servicing mission initially planned for 2004 was canceled.

NASA at one point was planning to abandon the telescope, hugely popular among astronomers. After an outcry, the U.S. space agency relented and a final Hubble servicing mission is scheduled for August.
In 2013, the James Webb Space Telescope is scheduled to replace Hubble