# Tag Info

1

Space is mostly black, because most of space doesn't have light coming from it for you to see. The moon, being basically a big rock, unsurprisingly does not change this: You would expect that standing on a rock would not affect what you see. Earth is unusual in having a sky because it has an atmosphere. The atmosphere is a bunch of gas that changes the ...

4

In addition to the lack of an atmosphere (the primary reason, already addressed in other answers), something that compounds the effect even further is that the lunar surface is quite reflective, and because the people who are taking the images of lunar surfaces often want to have Earth and/or astronauts in the shots and also be able to make out detail in the ...

11

With the atmosphere of the moon being $10^{14}$ times less dense than that of Earth, there is negligible scattering, so whereas on Earth, approximately 25% of direct solar radiation is scattered around (making the sky light up and appear blue), there is no mechanism for this on the moon, and all light from the sun travels (essentially) unaffected to the ...

21

The moon does have a night and a day, but this isn't as fully connected to your question as you might think. The moon is tidally locked with the earth, meaning that the same side always faces earth. Since the moon also orbits around the earth (with a period of a lunar month), this means each side changes, over the course of a lunar month, between facing ...

1

Some studies have suggested that the Earth may have had a second tiny moon, which later crashed into and merged with the bigger current Moon. This might explain the lopsided back and front faces of the Moon. The second moon may have orbited the Earth for between 10 million and 100 million years. This little moon was likely about 750 miles wide, which ...

0

Absolutely we could, and in fact, I strongly suspect that General Relativity was never used in the Apollo program. for one thing, the on-board navigation computers were nowhere near powerful enough to perform any useful calculation with GR. on the other hand, it's possible to measure the position of the moon to within a few centimeters (much more accurate ...

3

Consider that it would not be particularly difficult to do an Apollo-type landing if each of your relative velocity, range, and angular measurements were off by +/- 5%. You could simply make small iterative corrections along the way, until the absolute values were small enough to make the relative errors inconsequential. At worst you'd need to carry ...

42

The Jet Propulsion Laboratory has incorporated general relativistic effects in its numerical integration of the planets since the mid to late 1960s. For example, the JPL DE19 ephemeris, released in 1967, incorporated relativistic effects in its modeling of the solar system. This didn't help much. Had they ignored relativistic effects there would have been ...

22

A few sanity checks without actually computing anything: First, the error due to neglecting general relativity is so small that it didn't affect prediction of lunar eclipses and wasn't actually noticed anywhere except in Mercury's orbit (at least not until they purpose-built experiments to detect minor discrepancies). I know this doesn't give a completely ...

70

The trouble with orbital mechanics is that it rapidly gets exceedingly complicated and hard to make intuitive sense of. However I think there is a reasonably straightforward way to show how little effect GR has on an Earth-Moon transfer orbit. But this takes a little preparation so bear with me while I give a short introduction. I hope everyone who reads ...

24

I'll start the ball rolling on this one. My GR knowledge is probably not good enough to make this a truly satisfying answer... The gravitational acceleration for an object moving radially at non-relativistic velocities in the Schwarzschild metric is modified by a factor $(1 - r_s/r)(3[1-r_s/r] -2)$, where $r_s = 2GM/c^2 = 0.00885 m$ for the Earth. If we ...

3

The Moon's orbit would be nearly Keplerian were it not for the perturbing effects of the Sun. The time from perigee to perigee and from apogee to apogee wouldn't change, and the time from perigee to apogee would be exactly half the orbital period. What you are seeing are perturbing effects of the Sun on the Moon's orbit. If you use push the site you found, ...

1

Interesting question. The earth/moon system around the sun certainly changes speed as the earth gets closer to are farther from the sun, but the Earth/Moon orbit the sun together so the direct effect on the Moons orbit regarding the earth's Apogee and Perigee would probobly be small. I think a larger effect is the tidal effects on the moon's orbit around ...

1

As the moon is continually receding from the earth due to the tides, the end result will be a stable orbit. about 2.3 billion years from now, the increase of the Sun's radiation will have caused the Earth's oceans to vaporize,[13] removing the bulk of the tidal friction and acceleration. The orbit should be stable. But the sun will finally become a ...

0

The Sun will collide with the Earth. The orbits are stable. But in about 5 billion years, the Sun will run low on hydrogen and begin burning helium. This will make it expand and engulf the Earth.

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