# How would eclipses change (both solar and lunar) if the moon was half the distance from the Earth?

I'm working on building a fantasy world where the moon is in a lower orbit. I've already worked out the effect on tides; 4x stronger high tides slightly further apart, increased coastal erosion, more coastal towns like Le Mont St Michel isolated at high tide. I've also calculated that the orbital period of the moon would be 9.64 days meaning shorter "months". But I'm struggling to work out how regularly eclipses would occur and how they would be different.

If the moon was closer, the Earth's wobble would decrease, would this along with the increased size of the moon in comparison to the Earth and Sun mean there is a lunar eclipse every full moon and a solar eclipse every new moon?

I believe a total lunar eclipse would leave a ring of the moon visible around the shadow of the earth and a solar eclipse would be complete darkness with no corona visible, is this correct? How long would each last?

Assuming the moon stays the same size:

Total Solar eclipse before:

Total Solar eclipse after:

Pardon my lack of photoshop, those edges should be blurred.

There will be more solar eclipses - considerably more. The moon takes up about 3.5 more area of the sky, and moves about ~3 times as fast. Back of envelope astronomy says we'll go from 1-2 partial solar eclipses per year on average to about 20, and 0-1 total solar eclipses per year to about 8.

Eclipses will be ~3 times faster. On Earth, Temuco in Chile will get a 2:50 hour solar eclipse, 28 seconds will be total on 14 Dec 2020. On your planet, the eclipse will be about 55 minutes, about 55 seconds total (it's moving ~3 times faster, but is twice the size so starts a little sooner, and ends a little later).

Lunar eclipses will become more often. My home town of Adelaide will get a 5 hour total lunar eclipse on 26 May 2021. If the moon is ~3.5 times the size, and moving ~3 times as fast, the moon wont fully enter the Umbra, only 2/3rds will, the rest will only enter the Penumbra.

• 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 16:06
• 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.
– Ash
Sep 18, 2020 at 16:11
• 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 16:13
• 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 16:21
• 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 16:25