APOD: Martian Moon Eclipses Martian Moon (2024 Feb 26)

[APOD Robot]

Martian Moon Eclipses Martian Moon

Explanation: What if there were two moons in the sky -- and they eclipsed each other? This happens on Mars. The featured video shows a version of this unusual eclipse from space. Pictured are the two moons of Mars: the larger Phobos, which orbits closer to the red planet, and the smaller Deimos, which orbits further out. The sequence was captured last year by the ESA’s Mars Express, a robotic spacecraft that itself orbits Mars. A similar eclipse is visible from the Martian surface, although very rarely. From the surface, though, the closer moon Phobos would appear to pass in front of farther moon Deimos. Most oddly, both moons orbit Mars so close that they appear to move backwards when compared to Earth's Moon from Earth, both rising in west and setting in the east. Phobos, the closer moon, orbits so close and so fast that it passes nearly overhead about three times a day.

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[BobBataviaIL]

Occults.

[Cousin Ricky]

According to https://ssd.jpl.nasa.gov/horizons/app.html#/, the orbital period of Deimos is 1.263 Earth days (30.312 hours), which is longer than a Martian day. Therefore, Deimos would rise in the east, albeit very slowly.

[Robert posted the text below. Thanks, Robert! —CR]
Yes, this is correct. Thanks, and thanks also to several people who emailed this in, too. The text on the main NASA APOD has now been corrected.

[zendae1]

I guess AI doesn't know farther is the technically correct term when referring purely to physical distance, since AI is technical...

[Ann]

I guess AI doesn't know farther is the technically correct term when referring purely to physical distance, since AI is technical...

That's so? I'm not sure when to use farther or further.

Ann

[Chris Peterson]

I guess AI doesn't know farther is the technically correct term when referring purely to physical distance, since AI is technical...

Not really. (Of course, the idea of anything in English, which is a descriptive language, being "technically correct" is pretty marginal.) And it depends as well on whether we're talking American English or British English.

In any case, it is widely accepted usage that "further" can be used both literally and figuratively. It is generally seen as a minor error to use "farther" in the figurative sense, though. So the caption is perfectly acceptable English.

(What's AI got to do with anything?)

[Chris Peterson]

I guess AI doesn't know farther is the technically correct term when referring purely to physical distance, since AI is technical...

That's so? I'm not sure when to use farther or further.

Ann

You can always safely use "further". "Farther" is generally limited to physical distance.

[johnnydeep]

I guess AI doesn't know farther is the technically correct term when referring purely to physical distance, since AI is technical...

That's so? I'm not sure when to use farther or further.

Ann

You can always safely use "further". "Farther" is generally limited to physical distance.

Yeah, I didn't get the "AI" reference either. Is an APOD post ever generated by AI these days? (that's "AI" for Artificial Intelligence, not "Al" short for Albert I first read it!).

As for farther/further, there's a lot more here for the curious:

People use both further and farther to mean “more distant.” However, American English speakers favor farther for physical distances and further for figurative distances.

Farther vs. further: What’s the difference?

Part of the confusion between farther and further lies in the fact that these words can be adverbs, adjectives, or verbs, and the differences within each part of speech.

• Adverb: both words mean “more distance,” but only further can also mean, “additionally” (short for furthermore).
• Adjective: both words work as the comparative form of far, but only further can also mean “additional.”
• Verb: as a verb, further means “to advance” or “to progress;” farther cannot be used as a verb.

[Fatimfsel14]

Occults.

[johnnydeep]

Occults.

So tell me, are you and "BobBataviaIL" (who wrote the exact same comment above) one and the same?

[Chris Peterson]

Occults.

So tell me, are you and "BobBataviaIL" (who wrote the exact same comment above) one and the same?

In any case, both "occult" and "eclipse" are accurate terms in this case.

[Rauf]

I hope Mars can catch a new moon. He deserves a friend.

How about making Mars a moon of Earth? That would be nice.

[johnnydeep]

I hope Mars can catch a new moon. He deserves a friend.

How about making Mars a moon of Earth? That would be nice.

Nothing preventing it I suppose, but it would necessarily entail some extremely precise orbital mechanics in order to not completely destroy the Earth, Moon and Mars in the process! (I'm assuming we'd want the Moon to remain as a moon.) And it sure would make Mars exploration much quicker and easier!

[Chris Peterson]

I hope Mars can catch a new moon. He deserves a friend.

How about making Mars a moon of Earth? That would be nice.

Nothing preventing it I suppose, but it would necessarily entail some extremely precise orbital mechanics in order to not completely destroy the Earth, Moon and Mars in the process! (I'm assuming we'd want the Moon to remain as a moon.) And it sure would make Mars exploration much quicker and easier!

The result would be dynamically unstable, and can you imagine the tides? I doubt a 3-body system of Mars, Earth, and the Moon would allow for anything more complex than algae and bacteria to survive.

[johnnydeep]

How about making Mars a moon of Earth? That would be nice.

Nothing preventing it I suppose, but it would necessarily entail some extremely precise orbital mechanics in order to not completely destroy the Earth, Moon and Mars in the process! (I'm assuming we'd want the Moon to remain as a moon.) And it sure would make Mars exploration much quicker and easier!

The result would be dynamically unstable, and can you imagine the tides? I doubt a 3-body system of Mars, Earth, and the Moon would allow for anything more complex than algae and bacteria to survive.

I knew you'd probably say that. Many planets have more than one moon. Are those systems all ultimately unstable over, say a few hundred million years, or is the problem made a lot worse if the bodies are more comparable in mass (Moon = 1, Mars = 10x, Earth = 100x)?

[Chris Peterson]

Nothing preventing it I suppose, but it would necessarily entail some extremely precise orbital mechanics in order to not completely destroy the Earth, Moon and Mars in the process! (I'm assuming we'd want the Moon to remain as a moon.) And it sure would make Mars exploration much quicker and easier!

The result would be dynamically unstable, and can you imagine the tides? I doubt a 3-body system of Mars, Earth, and the Moon would allow for anything more complex than algae and bacteria to survive.

I knew you'd probably say that. Many planets have more than one moon. Are those systems all ultimately unstable over, say a few hundred million years, or is the problem made a lot worse if the bodies are more comparable in mass (Moon = 1, Mars = 10x, Earth = 100x)?

There are moons, and there are moons. The Earth and Moon is already bordering on a binary planet system, and that's certainly what we'd have with just the Earth and Mars... close to a trinary system with the Moon included! Pluto is the only similar planet in the Solar System. All the rest of the planets that have moons are not significantly influenced by the relatively tiny bodies orbiting them.

If Mars were orbiting the Earth, the system would have a barycenter outside the Earth. And the Moon would be trying to orbit that, as well. If you could get Mars and the Moon far enough from Earth, you could probably have a fairly stable system. But you can't, because we're too close to the Sun... which effectively creates a 4-body system! Probably the Moon would be ejected and we'd end up with a binary system of Earth and Mars orbiting the Sun, and the two would become tidally locked.

[johnnydeep]

The result would be dynamically unstable, and can you imagine the tides? I doubt a 3-body system of Mars, Earth, and the Moon would allow for anything more complex than algae and bacteria to survive.

I knew you'd probably say that. Many planets have more than one moon. Are those systems all ultimately unstable over, say a few hundred million years, or is the problem made a lot worse if the bodies are more comparable in mass (Moon = 1, Mars = 10x, Earth = 100x)?

There are moons, and there are moons. The Earth and Moon is already bordering on a binary planet system, and that's certainly what we'd have with just the Earth and Mars... close to a trinary system with the Moon included! Pluto is the only similar planet in the Solar System. All the rest of the planets that have moons are not significantly influenced by the relatively tiny bodies orbiting them.

If Mars were orbiting the Earth, the system would have a barycenter outside the Earth. And the Moon would be trying to orbit that, as well. If you could get Mars and the Moon far enough from Earth, you could probably have a fairly stable system. But you can't, because we're too close to the Sun... which effectively creates a 4-body system! Probably the Moon would be ejected and we'd end up with a binary system of Earth and Mars orbiting the Sun, and the two would become tidally locked.

Thanks for the further explication. Well, at least it would be cool to see as long as it lasted, which would likely still be quite long enough - if it happened tomorrow - to be useful for humankind, and likely far outlast our extinction.

[Rauf]

The result would be dynamically unstable, and can you imagine the tides? I doubt a 3-body system of Mars, Earth, and the Moon would allow for anything more complex than algae and bacteria to survive.

I knew you'd probably say that. Many planets have more than one moon. Are those systems all ultimately unstable over, say a few hundred million years, or is the problem made a lot worse if the bodies are more comparable in mass (Moon = 1, Mars = 10x, Earth = 100x)?

There are moons, and there are moons. The Earth and Moon is already bordering on a binary planet system, and that's certainly what we'd have with just the Earth and Mars... close to a trinary system with the Moon included! Pluto is the only similar planet in the Solar System. All the rest of the planets that have moons are not significantly influenced by the relatively tiny bodies orbiting them.

If Mars were orbiting the Earth, the system would have a barycenter outside the Earth. And the Moon would be trying to orbit that, as well. If you could get Mars and the Moon far enough from Earth, you could probably have a fairly stable system. But you can't, because we're too close to the Sun... which effectively creates a 4-body system! Probably the Moon would be ejected and we'd end up with a binary system of Earth and Mars orbiting the Sun, and the two would become tidally locked.

Still, what a sight to see in the sky Plus, having Mars nearby would make it easier for certain billionaires to colonize Mars.