2. The libration of the Moon over a single lunar month.
What if the moon had never formed?
Credit: Karl Tate / Life’s Little Mysteries
Huge tides generated by the moon – which orbited much closer to Earth when it formed – washed the chemical building blocks for life from land into the oceans and helped stir up the primordial soup. Without it, life may never have arisen, or living things would have very different behavioral patterns to cope with the six-hour day and extreme climate changes that would exist on a moonless Earth. [Get the full explanation]
In the Shadow of the Moon: A Lunar View of an Eclipse
The ISS Crosses the Moon
Credit: Phil McGrew
Photographer Phil McGrew said this photograph of the International Space Station traversing the face of the moon was the most technically challenging photograph he’s ever taken. The shot involved a lot of data triangulation to make sure McGrew would be in the right place to see the ISS cross, visible here as a series of tiny dots. “Even if you miss it by half a mile the space station wont be across the moon,” McGrew told LiveScience.
The Moon sets behind the temple of Poseidon at Sounio
Following a Moon Shadow
Image courtesy PHL/UPR Arecibo
Seen from one of Japan’s MTSAT meteorological satellites, the shadow of the moon darkens part of the North Pacific during the annular solar eclipse last Sunday and Monday. Despite the diminutive shadow shown, the moon is actually a little bigger than a quarter the size of Earth.
An annular eclipse happens when the moon lines up between Earth and thesun, and when the dark moon’s apparent diameter is smaller than the visible disk of the sun, leaving a ring—or annulus—of fiery light around the edges.
(See more 2012 annular solar eclipse pictures.)
Approaching Enceladus near midnight
Cassini approached for its October 19, 2011 flyby of Enceladus from almost directly behind it — only the faintest sliver of crescent is illuminated. In the background, Saturn’s crescent sweeps past as Enceladus grows in Cassini’s view. Credit: NASA / JPL / SSI / animation by Emily Lakdawalla
Ring of fire
The Moon is the only natural satellite of the Earth, and the fifth largestsatellite in the Solar System. It is the largest natural satellite of a planet in the Solar System relative to the size of its primary, having a quarter the diameter of Earth and 1⁄81 its mass. The Moon is the second densest satellite after Io, a satellite of Jupiter.
Top 10 Amazing Moon Facts
1. The Big Whack
The moon formed as a result of a collision known as the Giant Impact or the Big Whack, scientists figure. It went like this: A giant Mars-sized object hit Earth 4.6 billion years ago shortly after the birth of the sun and the solar system. A cloud of vaporized rock was kicked up (a mix of Earth and the other object) and went into orbit around Earth. The cloud cooled and condensed into a ring of small, solid bodies, which then gathered together, forming the moon.
2. Earth makes the moon rise
Each day, though not at the same time, the moon comes up in the East and goes down in the West — much like the sun and other stars and for the same reason Earth rotates, on its axis, toward the East, pulling celestial objects into view and then forcing them to slip away. The moon also makes an orbital trip around Earth once every 29.5 days. In the sky, this gradual movement is eastward, though it’s not perceptible during any given observing session. It is, however, why the moon rises later each day, by about 50 minutes on average. That also explains why the moon sometimes rises in the evening and us up during the night, while at other times it’s up only or mostly during the day.
3. No dark side
Contrary to what you might have heard, there is no “dark side” of the moon. There is, however, a “far side” that we can’t see from Earth. Here’s why: Long ago, the Earth’s gravitational effects slowed the moon’s rotation about its axis. Once the moon’s rotation slowed enough to match its orbital period (the time it takes the moon to go around Earth) the effect stabilized. So the moon goes around the Earth once and spins on its axis once, all in the same amount of time, and it shows us just one face the whole time.
4. Gravity is much weaker
The moon is about 27 percent the size of Earth and far less massive. Gravity on the moon is only about 1/6 of that on Earth. If you drop a rock on the moon, it falls more slowly (and astronauts can hope much higher). If you weigh 150 pounds on Earth, you’d weigh 25 pounds on the moon.
5. Bigger and smaller full moons
The moon’s orbit around Earth is an oval, not a circle, so the distance between the center of Earth and the moon’s center varies throughout each orbit. At perigee (PEHR uh jee), when the moon is closest to Earth, that distance is 225,740 miles (363,300 kilometers). At apogee (AP uh jee), the farthest position, the distance is 251,970 miles (405,500 kilometers).
6. Pockmarked history
The craters on the moon reveal its violent history. Because there is almost no atmosphere and little activity inside the moon, the crater trace a record of impacts back billions of years (unlike Earth, which would have been just as violent back then, but the craters have all been weathered away or folded back into the planet). By dating the moon’s many craters, scientists figured out that the moon (and Earth) underwent a Late Heavy Bombardment around 4 billion years ago. The latest thinking on this pummeling is that life may have survived it, if biology had gotten a foothold that early.
7. Not round
The moon is not round (or spherical). Instead, it’s shaped like an egg. If you go outside and look up at the moon, one of the small ends is pointing right at you. And the moon’s center of mass is not at the geometric center of the satellite; it’s about 1.2 miles (2 kilometers) off-center. Earth, likewise, bulges in its midsection.
8. Caution! Moonquakes
Apollo astronauts used seismometers during their visits to the moon and discovered that the gray orb isn’t a totally dead place, geologically speaking. Small moonquakes, originating several miles (kilometers) below the surface, are thought to be caused by the gravitational pull of Earth. Sometimes tiny fractures appear at the surface, and gas escapes.
9. Tugging on the oceans
Tides on Earth are caused mostly by the moon (the sun has a smaller effect). Here’s how it works: The moon’s gravity pulls on Earth’s oceans. High tide aligns with the moon as Earth spins underneath. Another high tide occurs on the opposite side of the planet because gravity pulls Earth toward the moon more than it pulls the water.
10. Ciao, Luna!
As you read this, the moon is moving away from us. Each year, the moon steals some of Earth’s rotational energy, and uses it to propel itself about 1.6 inches (4 centimeters) higher in its orbit. Researchers say that when it formed about 4.6 billion years ago, the moon was about 14,000 miles (22,530 kilometers) from Earth. It’s now more than 280,000 miles, or 450,000 kilometers away. Meanwhile, Earth’s rotation rate is slowing down — our days are getting longer and longer. Eventually, our planet’s tidal bulges will be assembled along an imaginary line running through the centers of both Earth and the moon, and our planetary rotational change will pretty much cease. Earth’s day will be a month long. When this happens, billions of years from now, the terrestrial month will be longer — about 40 of our current days — because during all this time the moon will continue moving away.;
Supermoon as seen from the Philippines