APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

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APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by APOD Robot » Mon May 09, 2022 4:05 am

Image A Martian Eclipse: Phobos Crosses the Sun

Explanation: What's that passing in front of the Sun? It looks like a moon, but it can't be Earth's Moon, because it isn't round. It's the Martian moon Phobos. The featured video was taken from the surface of Mars a month ago by the Perseverance rover. Phobos, at 11.5 kilometers across, is 150 times smaller than Luna (our moon) in diameter, but also 50 times closer to its parent planet. In fact, Phobos is so close to Mars that it is expected to break up and crash into Mars within the next 50 million years. In the near term, the low orbit of Phobos results in more rapid solar eclipses than seen from Earth. The featured video is shown in real time -- the transit really took about 40 seconds,as shown. The videographer -- the robotic rover Perseverance (Percy) -- continues to explore Jezero Crater on Mars, searching not only for clues to the watery history of the now dry world, but evidence of ancient microbial life.

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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by Chris Peterson » Mon May 09, 2022 5:25 am

APOD Robot wrote: Mon May 09, 2022 4:05 am Image A Martian Eclipse: Phobos Crosses the Sun

Explanation: What's that passing in front of the Sun? It looks like a moon, but it can't be Earth's Moon, because it isn't round. It's the Martian moon Phobos. The featured video was taken from the surface of Mars a month ago by the Perseverance rover. Phobos, at 11.5 kilometers across, is 150 times smaller than Luna (our moon) in diameter, but also 50 times closer to its parent planet. In fact, Phobos is so close to Mars that it is expected to break up and crash into Mars within the next 50 million years. In the near term, the low orbit of Phobos results in more rapid solar eclipses than seen from Earth. The featured video is shown in real time -- the transit really took about 40 seconds,as shown. The videographer -- the robotic rover Perseverance (Percy) -- continues to explore Jezero Crater on Mars, searching not only for clues to the watery history of the now dry world, but evidence of ancient microbial life.

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I'm glad the caption calls it a transit. I wish an official video from Nasa used the proper term in its title.
Chris

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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by heehaw » Mon May 09, 2022 9:49 am

What a joy to see such a thing! Callooh callay ! Oh frabjous day!

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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by JohnD » Mon May 09, 2022 10:11 am

Strange effect, as the rim of Phobos crosses the sunspots. As they appear from behind the moon (30-36 seconds in) they 'jump' as if the image was distorted by an atmosphere, that Phobos doesn't have!

Is this an artefact, or a real effect, and if so, why?
John

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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by orin stepanek » Mon May 09, 2022 12:37 pm

330px-Phobos_colour_2008.jpg
Looks like scorch-marks on this side! Maybe had close encounter
with an atmosphere?
marsglobe_viking_960.jpg
Must have been quitye an event to create such a chasm!
shutterstock_246058558-1.png
Morning stretch and yawn! :lol2:
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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by JohnD » Mon May 09, 2022 1:12 pm

Orin,
Not the first time that we have discussed the 'geography' (phobography?) of Phobos!

There once was a prominent contributor here who used the name "craterchains". They believed that such formations on various moons and asteroids were evidence of interplanetary warfare in some previous age. That his very name described an altogether natural process by which those markings would have occurred was deeply ironic. We have seen in the Shoemaker-Levy comet's impact with Jupiter that objects may break up under tidal forces and crash into the source of that tide, in a line of impacts.

There was a later discussion, which we both contributed to: viewtopic.php?t=9038&hilit=Phobos+craterchains&start=25 where another keen protagonist of previous space going civilisations, "Fiery Ice", argued that the low density of Phobos meant it was hollow.

No need to postulate that Phobos once skimmed an atmosphere. Just that it was hit by objects breaking up under Mar's (or another's) tidal influence!

John

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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by bystander » Mon May 09, 2022 2:05 pm

JohnD wrote: Mon May 09, 2022 1:12 pm ... "craterchains"..."FieryIce"...
Two names that are probably better left undisturbed.
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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by Chris Peterson » Mon May 09, 2022 2:09 pm

JohnD wrote: Mon May 09, 2022 1:12 pm No need to postulate that Phobos once skimmed an atmosphere. Just that it was hit by objects breaking up under Mar's (or another's) tidal influence!
Indeed, the apparent bulk density of Phobos is so low that we conclude it is more of a rubble pile than a solid body. If would itself break up under tidal forces long before it could get low enough to skim atmosphere.
Chris

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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by johnnydeep » Mon May 09, 2022 9:05 pm

JohnD wrote: Mon May 09, 2022 10:11 am Strange effect, as the rim of Phobos crosses the sunspots. As they appear from behind the moon (30-36 seconds in) they 'jump' as if the image was distorted by an atmosphere, that Phobos doesn't have!

Is this an artefact, or a real effect, and if so, why?
John
I don't think I even see the effect you're referring to: no "jumping spots" that I can tell - well, maybe the first one that reemerges. Anyone else see it?
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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by orienteer6 » Tue May 10, 2022 12:10 am

I am disappointed to see APOD misuse the word eclipse. This is a transit, since the light of the sun is not even remotely blocked.

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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by Fred the Cat » Tue May 10, 2022 12:59 am

I think, in an earlier post, I used the word "transit", but the terms are ambigous. :?
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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by Chris Peterson » Tue May 10, 2022 1:17 am

Fred the Cat wrote: Tue May 10, 2022 12:59 am I think, in an earlier post, I used the word "transit", but the terms are ambigous. :?
Actually, the terms aren't ambiguous at all.
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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by Fred the Cat » Tue May 10, 2022 1:46 am

Chris Peterson wrote: Tue May 10, 2022 1:17 am
Fred the Cat wrote: Tue May 10, 2022 12:59 am I think, in an earlier post, I used the word "transit", but the terms are ambigous. :?
Actually, the terms aren't ambiguous at all.
You are correct but I frequently am ambiguous. :wink:
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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by orin stepanek » Tue May 10, 2022 12:00 pm

JohnD wrote: Mon May 09, 2022 1:12 pm Orin,
Not the first time that we have discussed the 'geography' (phobography?) of Phobos!

There once was a prominent contributor here who used the name "craterchains". They believed that such formations on various moons and asteroids were evidence of interplanetary warfare in some previous age. That his very name described an altogether natural process by which those markings would have occurred was deeply ironic. We have seen in the Shoemaker-Levy comet's impact with Jupiter that objects may break up under tidal forces and crash into the source of that tide, in a line of impacts.

There was a later discussion, which we both contributed to: viewtopic.php?t=9038&hilit=Phobos+craterchains&start=25 where another keen protagonist of previous space going civilisations, "Fiery Ice", argued that the low density of Phobos meant it was hollow.

No need to postulate that Phobos once skimmed an atmosphere. Just that it was hit by objects breaking up under Mar's (or another's) tidal influence!

John
Not to be mistook; but Craterchains & I are are on two different pages! I'm not a believer in star wars! I was just noting that the one end looked like it was scorched! :shock:
Orin

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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by JohnD » Tue May 10, 2022 12:21 pm

Indeed, orin! The very idea of linking your name with the other had not even dared to cross my mind!

But that 'atmosphere' effect as Phobos crosses past the sunspots. I've looked again and it is still there. Anyone else?
John

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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by johnnydeep » Tue May 10, 2022 7:59 pm

Chris Peterson wrote: Tue May 10, 2022 1:17 am
Fred the Cat wrote: Tue May 10, 2022 12:59 am I think, in an earlier post, I used the word "transit", but the terms are ambigous. :?
Actually, the terms aren't ambiguous at all.
Hmm - are there "partial transits" to go along with the well-known "partial eclipse"? Or is a partial eclipse better described as a partial transit?
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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by orienteer6 » Wed May 11, 2022 1:06 pm

If you were to be sitting on Luna during a solar eclipse, you would see a shadow cross over the Earth. The same is true during a partial eclipse, albeit it would graze the Earth's limb.
If you were sitting on Phobos during a transit, you would not see any change. It has to do with the penumbra and the umbra.

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Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)

Post by Chris Peterson » Wed May 11, 2022 2:18 pm

orienteer6 wrote: Wed May 11, 2022 1:06 pm If you were to be sitting on Luna during a solar eclipse, you would see a shadow cross over the Earth. The same is true during a partial eclipse, albeit it would graze the Earth's limb.
If you were sitting on Phobos during a transit, you would not see any change. It has to do with the penumbra and the umbra.
A partial solar eclipse does not occur because the umbra grazes the Earth's limb. It occurs because the observer is in the penumbra. During a total solar eclipse, most viewers will actually see a partial eclipse. From the Moon, you'll see the umbral shadow if there is one, or not if the umbra misses the Earth completely. A skilled observer may also detect the darkening of the penumbra.

In any case, however, from Phobos during this transit event you could see a shadow moving across the surface. All transits generate penumbral shadows, which are instrumentally detectable, and may well be visible to the eye, as well, depending on the depth of the transit.
Chris

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