# How striking would our moon be to a seasoned space traveler? **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [June 30, 2026, 12:37pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297 "2026-06-30T12:37:34Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![StarvingButStrong](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/starvingbutstrong/32/335_2.png) [@StarvingButStrong](https://boards.straightdope.com/u/StarvingButStrong)\ **Post date:** [June 30, 2026, 12:37pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/1 "2026-06-30T12:37:34Z")
Moons are apparently No Big Deal, going by just our solar system. Jupiter and Saturn alone have more than eighty each according to the last mention of it I saw. But those are BIG planets and the moons are relatively insignificant. While Earth is a comparatively little rocky planet with a HUGE moon in comparison. Do you think this would be striking to Joe Spaceman who has been zipping around exploring the universe? Would he say, WOW! They really hit the jackpot on moons??? (Just a random thought I woke up with this morning.) ---
**Author:** ![Elmer\_J.Fudd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/elmer_j.fudd/32/1211_2.png) [@Elmer\_J.Fudd](https://boards.straightdope.com/u/Elmer_J.Fudd)\ **Post date:** [June 30, 2026, 12:43pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/2 "2026-06-30T12:43:24Z")
There might be some debate whether it was a moon or a double planet but I suspect the most striking thing would be the presence of liquid water on the larger body. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 30, 2026, 1:09pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/3 "2026-06-30T13:09:45Z")
We don’t know. Most astronomers think that our moon, a large moon orbiting a rocky planet, is unusual. But we don’t have enough data to be sure of that, and we have no idea how unusual. Maybe it’s something that you’d only see in every four or five solar systems; maybe only one solar system in ten thousand has something like that. If the latter, then it would seem like we won a highly-implausible jackpot… but maybe the anthropic principle comes in, and the presence of the Moon somehow (probably via tides) increased the odds of intelligent life arising here. Or, heck, maybe our solar system is unusual in that three of our four large rocky planets don’t have large moons. ---
**Author:** ![StarvingButStrong](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/starvingbutstrong/32/335_2.png) [@StarvingButStrong](https://boards.straightdope.com/u/StarvingButStrong)\ **Post date:** [June 30, 2026, 1:30pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/4 "2026-06-30T13:30:14Z")
> [@Chronos](#): > > Or, heck, maybe our solar system is unusual in that three of our four large rocky planets don’t have large moons. Uh, which is the third? Mercury and Venus don’t, Earth and Mars do. Maybe Pluto even if it’s no longer a planet? ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [June 30, 2026, 1:32pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/5 "2026-06-30T13:32:23Z")
> [@StarvingButStrong](#): > > Uh, which is the third? Mercury and Venus don’t, Earth and Mars do. Both Phobos and Deimos are so tiny that they aren’t even spherical, I think Mars is the third. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [June 30, 2026, 1:40pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/6 "2026-06-30T13:40:35Z")
I thought that people from other worlds might be impressed by the idea of solar eclipses, which are only possible because the apparent size of the Sun and the Moon are almost exactly the same from the surface of our planet. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 30, 2026, 1:44pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/7 "2026-06-30T13:44:05Z")
That’s why I said “large moons”. The moons of Mars are so tiny, you can jump into orbit around Deimos. ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [June 30, 2026, 1:52pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/8 "2026-06-30T13:52:36Z")
My guess would be that the most “striking” sights would be unstable ones, and that any system that lasts in the long term is going to be fairly mundane to a seasoned space traveller. Sure, the moon is cool - but it was **way** cooler when it was hot. As in, when it was a molten chunk of debris that had just been ejected from the Earth a couple million years ago and hadn’t solidified yet, and when the loose debris from the impact still formed a ring around the Earth. Our gas giants with their herds of moons are cool, but the view was probably even cooler from the surface of an extremely close transiting moon on an unstable trajectory that formed when the gas giant did and was destined to fall in within a couple million rotations, or perhaps be ejected instead. These events are happening _right now_ somewhere in the galaxy; a “seasoned” space traveller with access to faster than light travel could go check them out. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [June 30, 2026, 1:54pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/9 "2026-06-30T13:54:21Z")
> [@Dewey\_Finn](#): > > I thought that people from other worlds might be impressed by the idea of solar eclipses, which are only possible because the apparent size of the Sun and the Moon are almost exactly the same from the surface of our planet. This. It’s quite possible that it’s unique for an inhabited planet to have a solar eclipse like ours. It’s not even permanent here; as the Moon slowly moves away from Earth [eventually](https://en.wikipedia.org/wiki/Solar_eclipse#Final_totality) we won’t get the total eclipses we do now. ---
**Author:** ![StarvingButStrong](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/starvingbutstrong/32/335_2.png) [@StarvingButStrong](https://boards.straightdope.com/u/StarvingButStrong)\ **Post date:** [June 30, 2026, 2:07pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/10 "2026-06-30T14:07:40Z")
Very interesting stuff. I’m especially struck by the idea of Deimos surrounded by a halo of children who only headed out to play hopscotch… ---
**Author:** ![Elmer\_J.Fudd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/elmer_j.fudd/32/1211_2.png) [@Elmer\_J.Fudd](https://boards.straightdope.com/u/Elmer_J.Fudd)\ **Post date:** [June 30, 2026, 2:08pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/11 "2026-06-30T14:08:31Z")
For an interstellar space traveler, it might be “triple peanut” interesting. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [June 30, 2026, 2:16pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/12 "2026-06-30T14:16:32Z")
Eh. The Moon could be about twice as big (or twice as close) as it is and still deliver a solar eclipse that shows corona during totality. And at one time in our past it probably was. The fact our Moon is just barely big/close enough to fully cover the sun _now_ is an interesting coincidence. Visit a couple million years ago or hence and that won’t be true. Then again, if a space traveler visits enough systems, they’ll see all sorts of coincidences we haven’t seen here in our little sample of 8 planets, a hundredish moons, and a few thousand identifiable asteroids. ---
**Author:** ![solost](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/solost/32/11776_2.png) [@solost](https://boards.straightdope.com/u/solost)\ **Post date:** [June 30, 2026, 2:19pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/13 "2026-06-30T14:19:17Z")
> [@StarvingButStrong](#): > > But those are BIG planets and the moons are relatively insignificant. While Earth is a comparatively little rocky planet with a HUGE moon in comparison. Jupiter and Saturn’s moons may be relatively insignificant in comparison to their planets, but compared to Earth’s Moon, some of those moons may be more interesting to a space traveling alien. Titan and Europa are both significantly larger than the Moon. Titan has seas of methane, and Europa seems to have liquid water underneath its frozen surface. More interesting than our dead rock of a Moon, maybe. ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [June 30, 2026, 2:19pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/14 "2026-06-30T14:19:46Z")
> [@StarvingButStrong](#): > > Very interesting stuff. I’m especially struck by the idea of Deimos surrounded by a halo of children who only headed out to play hopscotch… It’s not quite a hop, you have to sprint. Actually, if you got a sphere of iron the same weight as Deimos (it would be quite a bit smaller since Deimos is not very dense) you could play a pretty interesting sport game on the surface. Gravity would be higher, since the surface is closer to the center of mass, but I think you could still kick a ball into orbit. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [June 30, 2026, 2:21pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/15 "2026-06-30T14:21:06Z")
> [@LSLGuy](#): > > The fact our Moon is just barely big/close enough to fully cover the sun _now_ is an interesting coincidence. Wasn’t that the point @Der_Trihs and I were making? And actually, I had the idea of writing a science-fiction story in which the supposed aliens visiting Earth were only here for eclipse viewing parties, though some came a little early or stayed a little late. ---
**Author:** ![Elmer\_J.Fudd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/elmer_j.fudd/32/1211_2.png) [@Elmer\_J.Fudd](https://boards.straightdope.com/u/Elmer_J.Fudd)\ **Post date:** [June 30, 2026, 2:29pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/16 "2026-06-30T14:29:21Z")
> [@StarvingButStrong](#): > > While Earth is a comparatively little rocky planet with a HUGE moon in comparison. Although it’s been “demoted” the Pluto/Charon system overwhelmingly beats the Earth/Moon in that way. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [June 30, 2026, 2:31pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/17 "2026-06-30T14:31:41Z")
Perhaps I misunderstood. But he said solar eclipses are only possible when the moon and star have (almost) the same angular size as seen from the planet. My point was “Nope. All that’s required is that the moon’s angular size be \>= the star’s. Not equal and only equal.” Now in a sense there’s an upper limit on the angular size of a moon that can produce interesting eclipses. Once the moon appears so large that it hides not only the bright photosphere, but also the dim corona, well then your eclipse starts looking more like “night”. Of course different stars of different classes have different relationships between size of photosphere and size of corona. Which in turn affects the size range of moons that will produce pretty eclipses. I suppose a good eclipse also requires that the planet be close enough to the star that the star has appreciable angular extent. From e.g. Neptune, the Sun looks like a welding arc. Still stupid bright, but almost a point, not a discernable disc. For a star like that, it’d be more correct aesthetically speaking to call a moon’s passage in front of the star an occultation than an eclipse. ---
**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\ **Post date:** [June 30, 2026, 2:38pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/18 "2026-06-30T14:38:08Z")
> [@LSLGuy](#): > > The fact our Moon is just barely big/close enough to fully cover the sun _now_ is an interesting coincidence. Visit a couple million years ago or hence and that won’t be true. The two parameters in question (size and distance from the homeworld/primary) are _not_ so independent of each other: have a smaller or more distant moon (begetting only annular eclipses), and the angle of our rotational axis becomes too unstable over time, leading to wild swings in seasonal climate. But if it is too big (sky blotting total eclipses that may last for many minutes if not hours), it will slow down the rotational period of the primary more quickly, leaving to big swings in temperatures over the course of a day by the time intelligent life could develop. Both these extremes would make it more difficult for an intelligent species to evolve and eventually develop a spacefaring civilization. Thus what our putative alien would think would thus be contingent on how HIS home world developed and whether it too has a relatively large moon. Of course, he could have come from a moon orbiting a gas giant, but those will tend to have long days as well, in addition to possible high doses of radiation, making spaceflight if not pre-tech survival problematic. ---
**Author:** ![burpo\_the\_wonder\_mutt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/burpo_the_wonder_mutt/32/365_2.png) [@burpo\_the\_wonder\_mutt](https://boards.straightdope.com/u/burpo_the_wonder_mutt)\ **Post date:** [June 30, 2026, 2:44pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/19 "2026-06-30T14:44:34Z")
You just _know_ ETs are going to blow up the Earth/Luna because we obstruct their view of Venus. ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [June 30, 2026, 2:45pm UTC](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297/20 "2026-06-30T14:45:31Z")
> [@John\_DiFool](#): > > Of course, he could have come from a moon orbiting a gas giant, but those will tend to have long days as well, in addition to possible high doses of radiation, making spaceflight if not pre-tech survival problematic. That’s rather Terra-centric, I think. There’s no reason why completely alien biologies should be identical to our own. It’s entirely possible that radiation wouldn’t bother them, while something we consider mundane (like oxygen, which was once a servere problem on our own planet) poses an insurmountable challenge. Personally, I think in the cold dark reaches of the outer solar system, radiation presents a possible energy source for alien autotrophs that make up the base of a trophic pyramid. [Next page](https://boards.straightdope.com/t/how-striking-would-our-moon-be-to-a-seasoned-space-traveler/1031297.md?page=2)