Timeline for How would eclipses change (both solar and lunar) if the moon was half the distance from the Earth?
Current License: CC BY-SA 4.0
16 events
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| Sep 18, 2020 at 21:15 | comment | added | AlexP | OK, here is a picture. | |
| Sep 18, 2020 at 20:47 | comment | added | AlexP | Yes, if you move something closer to you it's going to appear twice as large. This holds both for the Moon and for the section of Earth's umbra crossed by the Moon's orbit. They will both appear twice as large. (Actually the section of the Earth's umbra will have a diameter more than twice as large, because the umbra is conical and it is actually larger at the closer distance.) Do you want me to draw a picture? | |
| Sep 18, 2020 at 17:12 | history | edited | Ash | CC BY-SA 4.0 |
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| Sep 18, 2020 at 17:11 | comment | added | Ash | @ AlexP No need to get rude - If I move something twice as close to me - it's going to appear larger in the 2D projection of the sky. It's basic trig, half the denominator into arctan, keep the numerator the same, angular diameter increases (it's about double 0.5 to 0.9). The umbra at that distance will also appear larger - same thing, the relevant angular diameter is about 15% larger. You're trying to fit a peg twice the size into a hole 15% larger - it's going to occur less. I'm going to delete that section of my answer cause it's not important. Feel free to put a better answer in. | |
| Sep 18, 2020 at 16:57 | comment | added | AlexP | The moon does not about doubles in diameter. It has the same diameter. And the umbra of Earth is bigger closer to Earth. I have no idea why you consider the angular diameter of the Moon, but not also the angular diameter of the relevant section of the umbra. Either work with the real diameters of both the Moon and the umbra, or else work with the angular diameters of both the Moon and the section of the umbra. Minus one for failing geometry. | |
| Sep 18, 2020 at 16:51 | history | edited | Ash | CC BY-SA 4.0 |
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| Sep 18, 2020 at 16:41 | vote | accept | Skoby | ||
| Sep 18, 2020 at 16:33 | comment | added | Ash | The umbra will go from ~9000km at moon distance to about ~10700km at the new one (12740km umbra at earth centroid. 9000km at current moon, linear interpolation ~10700), which from the point of view of earth will be about at 15% increase in diameter. The moon about doubles in diameter. | |
| Sep 18, 2020 at 16:25 | comment | added | Trish | Sadly, noone will see these megaeclipses, as the closer moon would not have allowed life in the way we know it - tides would also be much more rampant... | |
| Sep 18, 2020 at 16:21 | comment | added | ThisIsAQuestion | I agree, the moon will appear bigger to an observer on earth, and this will have a significant impact on solar eclipses. However, length of a lunar eclipse is dependent on the opposite: How big does the earth appear to someone on the moon? The bigger earth appears, the bigger earth's umbra at that distance. It may only be different by a small amount due to the difference in earth/moon distance vs earth/sun distance, but the umbra will still be slightly bigger. Combine this with the moon's newly increased speed and you should be getting total lunar eclipses more often than before. | |
| Sep 18, 2020 at 16:16 | comment | added | Ash | Closer to earth will make it take up more of the sky, which I've simplified down to "bigger". You're right, it wont get more mass, but the angular diameter will approximately double if the object is bought to half the distance. Change in sky surface area will go up about 3.5 times. | |
| Sep 18, 2020 at 16:14 | history | edited | Ash | CC BY-SA 4.0 |
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| Sep 18, 2020 at 16:13 | comment | added | ThisIsAQuestion | The moon in this question isn't bigger, it's just closer to earth. That means it will fit in the umbra more easily. | |
| Sep 18, 2020 at 16:11 | comment | added | Ash | The diagram is exaggerated, those lines are very close to parallel. The moon currently can fit entirely between the umbra and penumbra, but make the moon bigger and its an extremely tight fit. I'll add a diagram. | |
| Sep 18, 2020 at 16:06 | comment | added | ThisIsAQuestion | You beat me to answering, and with a better answer than mine was going to be. One question though: Since the moon is the same size but the umbra of the earth is larger at the moon's new distance, doesn't that mean total lunar eclipses will occur more often? | |
| Sep 18, 2020 at 16:00 | history | answered | Ash | CC BY-SA 4.0 |