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APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Mon May 09, 2022 4:05 am
by APOD Robot
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.
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Mon May 09, 2022 5:25 am
by Chris Peterson
APOD Robot wrote: ↑Mon May 09, 2022 4:05 am
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.
I'm glad the caption calls it a transit. I wish an official video from Nasa used the proper term in its title.
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Mon May 09, 2022 9:49 am
by heehaw
What a joy to see such a thing! Callooh callay ! Oh frabjous day!
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Mon May 09, 2022 10:11 am
by JohnD
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
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Mon May 09, 2022 12:37 pm
by orin stepanek
![330px-Phobos_colour_2008.jpg](./download/file.php?id=44184&sid=ba0886acfe9c3c0b49960abf0f2f771e)
- 330px-Phobos_colour_2008.jpg (20.16 KiB) Viewed 4758 times
Looks like scorch-marks on this side! Maybe had close encounter
with an atmosphere?
Must have been quitye an event to create such a chasm!
Morning stretch and yawn!
![Laughing :lol2:](./images/smilies/asterisk_laugh.gif)
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Mon May 09, 2022 1:12 pm
by JohnD
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
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Mon May 09, 2022 2:05 pm
by bystander
JohnD wrote: ↑Mon May 09, 2022 1:12 pm
... "craterchains"..."FieryIce"...
Two names that are probably better left undisturbed.
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Mon May 09, 2022 2:09 pm
by Chris Peterson
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.
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Mon May 09, 2022 9:05 pm
by johnnydeep
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?
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Tue May 10, 2022 12:10 am
by orienteer6
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.
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Tue May 10, 2022 12:59 am
by Fred the Cat
I think, in an earlier
post, I used the word "transit", but the
terms are ambigous.
![Confused :?](./images/smilies/icon_confused.gif)
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Tue May 10, 2022 1:17 am
by Chris Peterson
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.
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Tue May 10, 2022 1:46 am
by Fred the Cat
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 :wink:](./images/smilies/icon_wink.gif)
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Tue May 10, 2022 12:00 pm
by orin stepanek
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!
![Shocked :shock:](./images/smilies/icon_eek.gif)
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Tue May 10, 2022 12:21 pm
by JohnD
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
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Tue May 10, 2022 7:59 pm
by johnnydeep
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?
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Wed May 11, 2022 1:06 pm
by orienteer6
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.
Re: APOD: A Martian Eclipse: Phobos Crosses... (2022 May 09)
Posted: Wed May 11, 2022 2:18 pm
by Chris Peterson
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.