![]() ![]() The craters themselves, which have been preserved for billions of years, provide an impact history for the Moon and other bodies in the inner solar system. These light and dark areas represent rocks of different composition and ages, which provide evidence for how the early crust may have crystallized from a lunar magma ocean. The dark features, called maria (Latin for seas), are impact basins that were filled with lava between 4.2 and 1.2 billion years ago. The light areas of the Moon are known as the highlands. Plans are now under way for humans to return to the Moon through NASA’s Artemis program. Twelve humans have walked on the Moon (all astronauts in NASA’s Apollo program in the 1960s and 1970s).Some polar craters, darkened by permanent shadows, harbor hidden water ice. Pickering’s observations of the Moon lead to the belief that with such little atmospheric pressure, any ice on the lunar surface would near instantly sublimate. The coldest temperatures in the solar system have been recorded at the Moon’s poles. An open page of astronomer William Pickering’s book The Moon: A Summary of Our Satellite with a Complete Photographic Atlas.Tidal forces, meteoroid impacts, and thermal changes in rock near the surface all trigger seismic disturbances. Compared to Earth, the Moon is a quietly active world. The debris from this impact likely formed the Moon. Evidence suggests that, about 4.5 billion years ago, a Mars-sized object crashed into early Earth. 1,079.6 miles 1,737.5 kilometers Mass: 0.0123 of Earths (a bit more than 1 percent) Gravity: 0.166 of Earths (If you weigh 100 pounds (45 kilograms) on Earth, youd weight 16.6 pounds (7. ![]() Without plate tectonics or weather to erase evidence of its past, our closest neighbor in space preserves a record of the geologic history that has shaped our solar system – including our own planet. Earth’s Moon is a cornerstone of planetary science.From Earth, we always see the same face of the Moon because the Moon is spinning on its axis at the same speed that it is going around Earth (that is, it is in synchronous rotation with Earth). Every two weeks, we have to look in the opposite direction to see the Moon, and the ground beneath our feet is then tilted the opposite way as well.The Moon moderates Earth’s wobble on its axis, leading to a relatively stable climate over billions of years. The tilted ramp works the same as the tilted “platform” of the Earth beneath our feet. If you turn around, the horizon appears to tilt the opposite way. In front of you, the horizon looks higher on the right and lower on the left. Earth has a tilt of 23.5 degrees on its axis, which means that when we observe the Moon from Earth, it’s a little like we’re standing sideways on a ramp. The tilt of the Moon’s orbit contributes to this, but it’s mostly due to the tilt of our Earth. ![]() We call this motion “libration in latitude.”įinally, the Moon appears to tilt back and forth like a metronome. The 5 degree tilt of the Moon’s orbit also causes it to appear to nod, as though it were saying “yes.” The tilt sometimes brings the Moon above Earth’s northern hemisphere, and sometimes below Earth’s southern hemisphere, allowing us to see slightly more of the northern or southern hemispheres of the Moon. We call this motion “libration in longitude.” When the Moon is farthest from Earth and orbiting at its slowest, its rotation gets a little ahead, and we see a bit more of its western side. When the Moon is at its closest to Earth and moving most quickly along its orbital path, the Moon itself doesn’t rotate quite fast enough to keep entirely the same side facing us, and we get to see a little more of the eastern side of the Moon. The Moon’s rate of rotation around its own axis, though, always stays the same. Because the Moon's orbit is not perfectly circular, its distance from Earth and its speed in orbit both change slightly throughout the month. ![]()
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