# Tag Info

### Why can we see the moon when it is between the Earth and the Sun?

The premise of this question is wrong. If the moon is in between the earth and the sun (as shown on your diagram), and you can see the moon, then it is day, not night: If on the other hand, you are ...
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### Why does the full Moon appear?

The orbital plane of the Moon around the Earth is at an angle to the orbital plane of the Earth about the Sun. This diagram was drawn to show why we do not have eclipses more often but is also ...
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### Why does the full Moon appear?

One of the reasons people often have bad intuitions like yours about the relationship between the Earth and the Moon is because they've never seen an accurate picture. The distance from the Earth to ...
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### Is there a maximum distance from a planet that a moon can orbit?

The concept you're looking for is that of a planet's Hill sphere. If a planet of mass $m$ is in a roughly circular orbit of radius $a$ about a star of mass $M$, then the radius of this "sphere&...
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### Why doesn't the Moon disrupt the orbits of geostationary satellites?

The moon absolutely disrupts the orbit of a geostationary satellite. Just as the moon can cause tides on the Earth's surface, the moon's gravitational pull on a satellite will cause it to begin to ...
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### If you sliced the moon in half perfectly, would it hold together?

Assuming you don't separate the halves to any great extent, it would immediately fuse back together due to its self-gravity. The tidal forces exerted by the Earth on the Moon are only sufficient to ...
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### How can a full moon be seen south of an observer's location?

Here is a picture that may help in describing this. First row: Sun (red), Earth (blue) and Moon (black) to scale (axes - in km). You can see just how far away the sun is... and on this scale the ...
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### Why can we see the moon when it is between the Earth and the Sun?

The sun doesn't just illuminate the moon directly. The moon is also illuminated by sunlight reflected from the earth. This is called earthshine. This makes the parts of the moon that face us ...
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### If the moon had a mirror surface, would the earth be equally illuminated as by the sun during full moon, or would it require a different mirror shape?

No, because of the sizes of their surfaces. Let's make these simplified assumptions: The Earth and the Moon are both spheres 1 AU from the Sun. The total amount of sunlight an object receives is ...
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### If the moon became a black hole, how much would it eat in a day?

It'd suck in very little mass. One thing to understand about black holes is that they have super-strong gravity, but only when you are very close to their event horizon. Otherwise they're just normal ...
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### How does a laser from Earth manage to hit the Moon with precision?

Commenters on the first version of this answer (preserved in the edit history) did me the favor of finding the literature that I hadn't read for years, which contains a succinct answer to your ...
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### If the tidal bulge on the earth speeds the moon up, how does the moon move to a higher orbit?

To understand this, let’s start with a simpler example of orbital mechanics. Suppose we have a rocket in a circular orbit that wishes to transfer to a higher circular orbit. This proceeds in the ...
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### If the moon had a mirror surface, would the earth be equally illuminated as by the sun during full moon, or would it require a different mirror shape?

You seem to be asking if the reflection of the sun from a spherical mirror, a convex surface would be the same as the reflection from a flat mirror. A convex mirror is dispersive The image in ...
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### How can a full moon be seen south of an observer's location?

To answer the question, your friend needs to understand that the sun is not a little thing on the other side of the globe. It is very large, and it only looks small because it is far away. Also the ...
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### What is a simple argument to prove that the stars in the sky are further away from the Earth than the Moon?

The fact of parallax in the observed position of the moon was known in ancient times. This makes possible a calculation of the distance of the moon in terms of Earth radii. No parallax was then ...
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### White full moon reflected orange-red light off of Atlantic Ocean surface. Why is this?

You would probably be about 9 to 12 km high, above the bulk of the atmosphere. The blue part of the light from the moon is more diffused travelling through the atmosphere and back, leaving the red ...
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### What does "rarely" mean in NASA's statement: "technically referred to as an exosphere because it’s so thin, its atoms rarely collide."?

Any given gas molecule goes a long way on average without colliding with another gas molecule. The mean free path for a gas molecule is on the order $$\lambda\sim \frac{k_BT}{d^2p}$$ where $k_B$ is ...
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### What is a simple argument to prove that the stars in the sky are further away from the Earth than the Moon?

Lunar occultations. Just missed the moon block Mars last month. Not sure when Mars will block a star, thereby proving the stars are further than the moon.
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### Why is it so dark during a solar eclipse?

The most significant difference is that in a total eclipse the moon obstructs the sun's light outside of earth's atmosphere whereas at sunset, the light is obstructed by the horizon within the ...
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### What does the sky look like from the moon?

Quote from Buzz Aldrin: “Obviously, when we touched down on the moon, we were very relieved. The immediate surface was very powdery, as best we could see looking down from 15 feet. Off in the ...

### Why does a full moon seem uniformly bright from earth, shouldn't it be dimmer at the "border"?

If the moon were a uniform sphere, it would indeed appear dimmer at the edges of a full moon. Surface roughness is the main reason the edges are not as dim as the sphere model predicts. When viewing ...
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### How long is a second on the moon?

The time dilation is mainly gravitational and, to a first approximation, calculated by the Schwarzschild metric, which is c^2\mathrm{d}\tau^2 = -\left(1-\frac{r_S}{r}\right)c^2\mathrm{d}t^2 + \left(...
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### Why can we see the moon when it is between the Earth and the Sun?

While excellent answers have already been provided (yes, it's Earthshine; yes, when the Moon is between the Sun and the Earth, you don't see the Moon at night, you see it from the daylit side of the ...
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### If the moon became a black hole, how much would it eat in a day?

It would suck in basically nothing. If the mass of the moon were concentrated in a black hole, you could draw a sphere around that black hole the size of the moon, and for everything outside that ...

### Why didn't the debris collapse back into the Earth at the time of Moon's formation?

A lot of debris has probably fallen back to earth. To stay in orbit you need enough angular momentum to overcome attraction. But if the collision happened at an angle a portion of the debris could ...

### How does a laser from Earth manage to hit the Moon with precision?

As Rob mentions, when reflecting a laser off the Moon you do need to compensate by ~1.4 arc-seconds for the light-time delay. But the whole point of the Lunar Laser Ranging experiments (LLR) is to ...
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### Why does a full moon seem uniformly bright from earth, shouldn't it be dimmer at the "border"?

For the full moon, the answer in the OP is clearly correct, as others have confirmed: the brightness is related to the solar energy per square foot, and when viewing from the front, the square feet ...
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### If you sliced the moon in half perfectly, would it hold together?

General relativity is a more accurate theory than Newton's mechanics/gravity for calculating gravitational effects. But here, since we are dealing with a low-speed problem in the weak-field limit, the ...
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