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Greg Egan

“No planet in our solar system experiences a total solar eclipse by one of its moons, where the moon completely covers the sun from an observer's perspective on the planet's surface.”

That will disappoint a lot of people in April.

This whole answer is amusingly addled. I doubt many humans would construe this question to mean “Can a planet’s moon ever block out the sun completely *across the entire planet*?”

FWIW, at the top of Jupiter‘s atmosphere Ganymede looks about two-and-a-half times bigger than the sun.

Question: From the top of the atmosphere of which planets in the solar system can the sun ever be wholly obscured by one of the planet’s moons? Gemini: No planet in our solar system experiences a total solar eclipse by one of its moons, where the moon completely covers the sun from an observer's perspective on the planet's surface. Here's why: Relative Sizes: Compared to their host planets, moons in our solar system are significantly smaller. Orbital Distances: Moons also orbit much closer to their planets compared to the Sun-planet distance. These factors together ensure that no moon can cast a shadow large enough to completely engulf the entire planet, blocking the sun entirely. Additional points: While some moons like Jupiter's Ganymede and Saturn's Titan are larger than the planet Mercury, their orbital distances are still significantly smaller than the Sun-planet distance, preventing a total eclipse. Even on Earth, where the Moon is relatively large and close, the Moon's shadow only covers a small portion of the Earth's surface during a total solar eclipse. Therefore, no planet in our solar system experiences a complete solar eclipse caused by its moon.
13 Mar 2024 at 12:27 | Open on mathstodon.xyz
11 comments
Colin the Mathmo

@gregeganSF You have to know what it means in order to understand the answer.

In other words ...

You have to know what it means to know what it means.

Just ... bonkers.

13 Mar 2024 at 12:40 | Open on mathstodon.xyz
Thomas Favre-Bulle 🏳‍🌈
Greg Egan

@erispoe So it gets the geometry right, but then inserts its own reinterpretation of the question where the moon needs to subtend almost exactly the same angle as the sun, which was not what I asked about.

13 Mar 2024 at 12:45 | Open on mathstodon.xyz
Evannakita

@gregeganSF If you’re interested, here are a few mock-ups I made a little while back of eclipses on Jupiter!

mastodon.online/@evannakita/11

13 Mar 2024 at 13:20 | Open on mastodon.online
Greg Egan
Evannakita

@gregeganSF @evannakita Thank you! I made this ‘cause I was planning a story about sky pirates in the Jovian atmosphere, and I wanted a scene during an eclipse. I later relocated the story to Saturn, though, so these aren’t relevant to it anymore, but I’m still very glad to have made ‘em :D

13 Mar 2024 at 13:25 | Open on mastodon.online
Eleder

@gregeganSF This reminds me to the old joke "Which Solar System planet can NOT be observed through a telescope?" 🙂

13 Mar 2024 at 13:25 | Open on frikiverse.zone
Kagan MacTane (he/him)

@gregeganSF There's also the part where everything it says about orbital distances seems to get parallax backwards, claiming that because the moons are so close to their parent planets, they can't cover the whole sun.

13 Mar 2024 at 15:18 | Open on wandering.shop
Juan Carlos Muñoz

@gregeganSF One day we'll find out that the servers behind these AI chatbots are just a room full of reply-guys typing on a computer. I'm not going to use the usual "monkeys with a typewriter" metaphor because I'm pretty sure even monkeys would do a better job at answering these questions.

13 Mar 2024 at 15:19 | Open on mastodon.online
DELETED

@astro_jcm @gregeganSF Reply-guys would come to more logical conclusions.

13 Mar 2024 at 16:21 | Open on mastodon.social
jz.tusk

@gregeganSF

Could you mark stuff like this as "AI generated" in the future, even though you're posting it just to show how bad it is? There are lots of us who are avoiding it like the plague, and so don't instantly recognize the source from appearance of the screen, and so have to spend time figuring out that it is AI nonsense. Thanks!

13 Mar 2024 at 15:53 | Open on mastodon.social
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