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.