The outermost part of the crust is broken and jumbled due to all the large impacts it has received, a shattered zone that gives way to intact material below a depth of about 6 miles 9. Like the four inner planets , the moon is rocky. It's pockmarked with craters formed by asteroid impacts millions of years ago. Because there is no weather, the craters have not eroded.
The average composition of the lunar surface by weight is roughly 43 percent oxygen, 20 percent silicon, 19 percent magnesium, 10 percent iron, 3 percent calcium, 3 percent aluminum, 0. Orbiters have found traces of water on the lunar surface that may have originated from deep underground. They have also located hundreds of pits that could house explorers who remain on the moon long-term. Our Changing Moon ].
Ongoing observations from the Lunar Reconnaissance Orbiter LRO showed that water is more abundant on slopes facing the lunar south pole , although scientists do caution that the water quantity is comparable to an extremely dry desert. Meanwhile, a study suggested the moon's interior could be abundant in water , too. The moon has a very thin atmosphere , so a layer of dust — or a footprint — can sit undisturbed for centuries. And without much of an atmosphere, heat is not held near the surface, so temperatures vary wildly. Daytime temperatures on the sunny side of the moon reach degrees F C ; on the dark side it gets as cold as minus F minus C.
The moon's gravity pulls at the Earth, causing predictable rises and falls in sea levels known as tides. To a much smaller extent, tides also occur in lakes, the atmosphere, and within Earth's crust. High tides are when water bulges upward, and low tides are when water drops down. High tide results on the side of the Earth nearest the moon due to gravity, and it also happens on the side farthest from the moon due to the inertia of water.
Low tides occur between these two humps. The pull of the moon is also slowing the Earth's rotation, an effect known as tidal braking, which increases the length of our day by 2. The energy that Earth loses is picked up by the moon, increasing its distance from the Earth, which means the moon gets farther away by 1. The moon's gravitational pull may have been key to making Earth a livable planet by moderating the degree of wobble in Earth's axial tilt, which led to a relatively stable climate over billions of years where life could flourish. The moon doesn't escape from the interplay unscathed.
A new study suggests that Earth's gravity stretched the moon into its odd shape early in its lifetime. During eclipses, the moon, Earth and sun are in a straight line, or nearly so. A lunar eclipse takes place when Earth gets directly or almost directly between the sun and the moon, and Earth's shadow falls on the moon.
A lunar eclipse can occur only during a full moon. Total Lunar Eclipse of Oct. A solar eclipse occurs when the moon gets directly or nearly directly between the sun and Earth, and the moon's shadow falls on us. A solar eclipse can occur only during a new moon. Solar eclipses are rare in a given location because the shadow of the moon is so small on the Earth's surface. The last total solar eclipse in the United States happened in Aug. The Earth's axis of rotation is tilted in relation to the ecliptic plane, an imaginary surface through Earth's orbit around the sun.
This means the Northern and Southern hemispheres will sometimes point toward or away from the sun depending on the time of year, varying the amount of light they receive and causing the seasons. The tilt of Earth's axis is about As such, the moon virtually has no seasons. This means that some areas are always lit by sunlight, and other places are perpetually draped in shadow. Some ancient peoples believed the moon was a bowl of fire, while others thought it was a mirror that reflected Earth's lands and seas, but ancient Greek philosophers knew the moon was a sphere orbiting the Earth whose moonlight reflected sunlight.
The Greeks also believed the dark areas of the moon were seas while the bright regions were land, which influenced the current names for those places — "maria" and "terrae," which is Latin for seas and land, respectively.enter
Moonbow - Wikipedia
The pioneering astronomer Galileo Galilei was the first to use a telescope to make scientific observations of the moon, describing in a rough, mountainous surface that was quite different from the popular beliefs of his day that the moon was smooth. In , the Soviet Union sent the first spacecraft to impact the moon's surface and returned the first photographs of its far side. This spurred a series of uncrewed missions by both the Soviet Union and the United States to observe the moon's surface. Many of these first probes were failures or only partially successful. However, over time, these early probes returned information about the moon's surface and geological history.
Luna 2 was the first spacecraft to impact the moon in The first soft landing was achieved in , by Luna 9. The United States sent astronauts to the moon's orbit and surface in the s and s. The first mission to the moon was in , when the Apollo 8 astronauts orbited it. In , Apollo 11 landed the first astronauts on the moon , undoubtedly the most famous of NASA's achievements, followed by five more successful missions and one, Apollo 13, that didn't make to the moon.
Their efforts returned lbs. Perhaps there are other times when the signal is prominent, and if so, on which nights should we expect to detect it?
Why Does the Moon Shine?
Our first reaction, at this point, might be that we should look for the spectral signature of vegetation on clear nights, with few clouds. Earthshine, we need remember, is not derived from our particular location, where clouds may or may not be present, but is a reflection of a large segment of the Earth. Earth, in other words, will be about equally cloudy no matter what day we choose to conduct our observations. The signal would appear, strong and clear and then disappear, and so repeatedly up to three times in succession. When the authors examined the data for those dates, they found that the three peaks corresponded to times when the regions contributing most to the earthshine included the plant-rich regions of Asia, Africa, and South America in succession.
On these dates at least the earthshine spectrum strongly suggested the presence of plant life on Earth. Just as the Moon waxes and wanes when seen from the Earth, depending on which part of it is lit by the Sun, so the Earth waxes and wanes every month when viewed from the Moon. Naturally, only the brightly lit areas of the surface of the Earth which are seen from the Moon contribute to earthshine. Inevitably, a large proportion of this area is covered with clouds, and it is likely to be composed of both land and water regions.
Even as the Earth turns on its axis, reflecting light from different continents and oceans towards the Moon, the overall effect does not change much. But when only a tiny sliver of the Earth contributes to earthshine, the case is different. As the Earth rotates, this sliver will be composed of oceans and continents in succession.
Because it is so narrow, however, it is unlikely to contain large swathes of both at the same time. When it is over the Americas, for example, a large percentage of the light reflected towards the Moon will indeed originate from the American landmass rather than from the Atlantic and Pacific Oceans. The same applies for the problem of cloud coverage.
On most days, areas covered by clouds contribute a large and more or less fixed proportion of light to the earthshine.
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But when the contributing segment of the Earth is composed only of a thin sliver, things are different. At other times, however, the thin sliver will pass over areas that are clear of clouds, and if those coincide with high vegetation regions then the spectral signature of plant-life will be easily detectable.
Conversely, when it passes over oceans, no such signal will be discernable.
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This is sufficient to provide the rough topographical resolution evident in the earthshine of December 19, , and December 7, Earthshine in general is a poor indicator of the abundance of plant life on our planet. What does all this teach us about detecting life on extrasolar planets? At first sight, it seems, not much. Earthshine, after all, is determined by the unique geometry of the Earth — Moon system, and its relation to the Sun.
When future missions will attempt to measure the light from distant planets, they will surely look for light reflecting directly off a planet, not light bounced off a hypothetical moon. Indeed, separating the light from a distant planet from that of its star is enormously difficult in itself; detecting light from the planet that is, in turn, bounced off a moon, is quite impossible. The case of earthshine would appear to be unique.
As the planet orbits its star, it eventually arrives at a point where it is closest to us, positioned in between Earth and its star. At that point the planet disappears from our view, since it reflects all the light back towards its star. As it happens, those are also the times when the planet is particularly close to the star, as seen from Earth, since it is just before or after it passes right in front of the star.
The combination of a very faint planet, positioned very close to its star, will make it exceedingly difficult to isolate the light from the planet from that coming directly from the star. Even if the current generation of missions is not sensitive enough to take advantage of this, other missions, ever more advanced and sensitive, will undoubtedly follow. And when they do we just might find that our Earth is not alone but a member of a large galactic family of planets, all of them green, rich in water, and teeming with life. Become a member of The Planetary Society and together we will create the future of space exploration.
The green line represents a computer modeling of the spectrum for the same date, showing excellent agreement with the observed spectrum. The red line represents the modeled spectral albedo for December 7, at The "red edge" is represented by the slope of the line between nm and nm.
Note that the slope for December 7, marked by the broken line, is much steeper than that for November