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39 votes
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Why were both the sun and the moon red today?

Smoke. There was significant smoke across the USA, which attenuated the light from the sun/moon due to increased scattering. The smoke particles effectively cause the light to reflect in different ...
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22 votes
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Can living where (rare) earth magnetic ore is abundant provide any protection from cosmic radiation?

Absolutely not. First of all, "rare earth magnet ore", meaning the ores of metals like neodymium (Nd) and samarium (Sm), is not magnetic at all. It only becomes a magnet once you make a ...
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20 votes
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Is there geological evidence that the moon once collided with the Earth?

Is there geological (or other physical) evidence here on Earth that confirms the moon once collided with the Earth? No, there isn't. This is, however, plenty of evidence that the moon formed due to a ...
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12 votes
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Why does helium-3 stay in the moon and not escape from it?

The Moon is not "full" of helium-3. 3He is at most fifty parts per billion of the lunar regolith1 and that "high" concentration pertains only to permanently shadowed craters. The Moon is bombarded by ...
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11 votes

Can living where (rare) earth magnetic ore is abundant provide any protection from cosmic radiation?

No. Cosmic radiation are high-energy particles that create particle showers high up in the terrestrial atmosphere. Those particle shower are heavily beamed downwards, and although in principle some ...
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10 votes
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How come the tide is low when the moon is high in the sky

This is based on the overly-simplified model of tides being the result of tidal bulges. As I explained in my answer to a related question on the physics.SE sister site, those tidal bulges do not and ...
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  • 20.4k
8 votes

Which Earth minerals would Moon colonists miss the most?

The composition of Moon rocks is pretty much the same as that of Earth. However, none of the processes that concentrate specific minerals in one location (i.e. into a mineral deposit useful for mining)...
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7 votes
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Can the moon shadow angle change?

Yes. The moon is lit by the sun, so as its position relative to the sun changes, so does the angle from which it is lit. I recommend reading the Wikipedia page on lunar phase for a good overview, ...
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6 votes

How is it possible that only the bottom half of the moon was showing?

It depends on the season and even more on latitude. At any given time, the same side of the Moon faces the Sun. Where you stand on Earth doesn't change which part of the Moon is lit, but if you ...
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  • 5,727
6 votes

Which Earth minerals would Moon colonists miss the most?

It is unlikely anything other than salt would be derived from sea water. The largest deposit of gold is dissolved within the worlds oceans - in terms of tonnes of metal. The problem with extracting ...
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  • 21.8k
6 votes

What has been the influence of the moon on Earth's temperature?

The complications of calculating the moon's contributions to earth's heat budget are touched on in Emergence of a Habitable Planet (2007) by Zahnle, et.al. in Space Science Reviews, a paper trying to ...
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  • 3,129
6 votes

How to make a Python function return the Moon's gravitational force (acceleration) to calculate orbits?

From my understanding, it should be possible to follow a similar procedure as what is done for calculating the gradient of gravity potential for the Earth (ignoring the potential corrections due to ...
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  • 233
5 votes
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What is the difference between lunar and earth soil

The single biggest difference is the lack of chemical weathering in lunar soils which are subject to physical weathering almost exclusively. If you exclude biological processes, terrestrial rocks ...
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5 votes

Why are there craters on the moon?

I'd like to expand on jamesqf's answer. But first, lit side of the moon and the dark There are no "lit" and "dark" sides of the moon. It rotates, and whatever is dark now will be lit in two weeks ...
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5 votes
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What is the Moon's distance from viewer at horizon?

What is the Moon's distance from viewer at horizon? As noted by others, the moon follows an elliptical orbit, which will lead to the greatest change in distance regardless of the observation angle. ...
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4 votes

What would happen if we removed Earth's moon?

This has sat untouched for a while, so I did a quick search and found this article which sums it up nicely. They key factors with regard to earth science would be: 1) Less extreme tides. The tides ...
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4 votes

Who originated Taylor's axiom of lunar formation, and where?

Just a shot in the dark, as the journal in which this article has been published has no online presence and is not available in paper form in my institution, but it might refer to an article by a ...
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  • 5,278
4 votes

What is the Moon's distance from viewer at horizon?

The Moon's orbit is elliptical, not circular, and the maximum and minimum distance from the Moon to the center of the Earth (apogee and perigee, 405,385 and 363,630 km respectively) are much larger ...
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  • 1,673
4 votes
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Old moon in the new moon's arm

Yes, earthshine is completely normal. It is simply illumination of that part of the moon that is facing away from the sun. This illumination is sunlight that is reflected towards the moon by the Earth....
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4 votes

Can the moon shadow angle change?

The apparent angle of the moon is a function of the 28-day lunar orbit, the time of day/night one is looking at the moon, and the latitude from which it is viewed. So, for example, the current (14 May ...
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4 votes

Why are there craters on the moon?

There are craters on the Earth, Arizona's Meteor Crater being perhaps the best-known example. The reason that there aren't a lot more (obvious) ones is that the Earth has lots of dynamic processes, ...
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  • 1,698
4 votes
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What is the characteristic time of the loss of the Earth atmosphere, how can it be calculated?

Even in the exosphere, at 1800 deg centigrade, the only components of the Earth's atmosphere that can currently attain escape velocity are hydrogen (3 kg per sec), and and helium (next to nothing). ...
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4 votes
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What is the difference between a depleted mantle, and a fertile or enriched mantle?

Basically, a fertile mantle is a portion of mantle that has not experienced any melting. On the other hand, a depleted mantle has experienced partial melting, and subsequent extraction of this melt. ...
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3 votes

Melting basalt on the lunar surface - what would the resulting material be like?

Melting lunar dust of basaltic composition will result (unsurprisingly) in basalt lava. There might be some volatile loss - if for some reason the basalt had some H2O or CO2 trapped in the solid you ...
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  • 22.2k
3 votes
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How much energy released by the Theia-Gaia impact?

Here's a quick-and-dirty estimate. The gravitational self-energy of a uniform-density sphere is $$ U = \frac35 \frac{GM^2}R $$ Let's assume Theia had the same mass and density as Mars, and that Gaia ...
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  • 431
3 votes

Old moon in the new moon's arm

You can think of it as the "reverse" of moonshine. When you walk outside at night and there's a full moon, you can actually see quite a lot around you. Same thing - this happens on the moon when ...
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  • 22.2k
3 votes

How often does the moon "set" for us compared to the sun?

As noted in comments, the earth rotates on its axis in about 23hrs 56 minutes. This is known as the sidereal day, that is, the day with respect to background stars. (that's not quite true, but it's ...
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