APOD: The Jellyfish and Mars (2021 May 19)

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APOD: The Jellyfish and Mars (2021 May 19)

Post by APOD Robot » Wed May 19, 2021 4:09 am

Image The Jellyfish and Mars

Explanation: Normally faint and elusive, the Jellyfish Nebula is caught in this alluring scene. In the telescopic field of view two bright yellowish stars, Mu and Eta Geminorum, stand just below and above the Jellyfish Nebula at the left. Cool red giants, they lie at the foot of the celestial twin. The Jellyfish Nebula itself floats below and left of center, a bright arcing ridge of emission with dangling tentacles. In fact, the cosmic jellyfish is part of bubble-shaped supernova remnant IC 443, the expanding debris cloud from a massive star that exploded. Light from that explosion first reached planet Earth over 30,000 years ago. Like its cousin in astrophysical waters the Crab Nebula supernova remnant, the Jellyfish Nebula is known to harbor a neutron star, the remnant of the collapsed stellar core. Composed on April 30, this telescopic snapshot also captures Mars. Now wandering through early evening skies, the Red Planet also shines with a yellowish glow on the right hand side of the field of view. Of course, the Jellyfish Nebula is about 5,000 light-years away, while Mars is currently almost 18 light-minutes from Earth.

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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by Ann » Wed May 19, 2021 6:09 am

Jellyfish Nebula and Mars annotated.png
Ah, perspective, perspective!

1. This is Mars. Mars is the brightest-looking orange light in this APOD. Mars is 18 light-minutes away in this APOD, like the distance from the Earth to the Sun and back, plus a little more. Mars shines by reflected light from the Sun and is a puny light-source indeed, bright-looking only because of its proximity.

2. This is Mu Geminorum, or Mu Gem. Mu Gem is the second-brightest orange light in the APOD. Mu Gem is some 230 light-years away, with an intrinsic V (yellow-green) luminosity of some 300 solar. The distance of 230 light-years makes Mu the second-closest annotated object in this APOD.

3, This is Eta Gem. Eta Gem is the third-brightest orange object in this APOD. Eta Gem is some 380 light-years away, with an intrinsic V luminosity of some 550 solar. The distance of 380 light-years makes Eta the third-closest annotated object in this APOD.

12 Gem.png
4. This is 12 Gem, a star of spectral class B9II, immersed in a blue reflection nebula. 12 Gem has a parallax of 0.5674 ± 0.0410 milliarcseconds. I tried to ask Google how far away such a parallax would put this star, but Google only offered me ways to calculate it, and I can't do that. So I'll have a guess. Maybe 3,000 light-years, some 10 times farther away than Eta and Mu Geminorum?

5. This is the Jellyfish Nebula, and the APOD caption says that this nebula is some 5,000 light-years distant. It is tempting to think that there may be a connection between the Jellyfish Nebula and 12 Gem. After all, 12 Gem is undoubtedly a massive star that probably started its life as a main sequence relatively early B-type star. (B3? B2?) Maybe a shock wave from the supernova blast compressed gas at the birth site of 12 Gem?

Or maybe, even more tantalizing, the progenitor star of the Jellyfish Nebula and 12 Gem may have belonged to the same cluster (or at least very adjacent clusters) of stars? Is that possible? Please note that the distance estimate for the Jellyfish Nebula is probably quite uncertain.

Ann
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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by orin stepanek » Wed May 19, 2021 11:46 am

Guenzel-JellyfishMars30APR2021_1000.jpg
Did I get the stars labeled right; Or did I reverse them? Mu and Eta Geminorum, stand just below and above the Jellyfish Nebula; I took it that below and above meant that Mu was the bottom star! If Ann is right than I have them reversed! I also missed spelled Mu! :oops: This is a nice picture & I noticed the cloud above the Jellyfish kinda, sorta looked like a man; so I had a little fun! :lol2:
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Last edited by orin stepanek on Wed May 19, 2021 11:57 am, edited 1 time in total.
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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by Ann » Wed May 19, 2021 11:54 am

orin stepanek wrote:
Wed May 19, 2021 11:46 am
Did I get the stars labeled right; Or did I reverse them? This is a nice picture & I noticed the cloud above the Jellyfish kinda, sorta looked like a man; so I had a little fun! :lol2:
Well, you actually mixed up Eta and Mu!

I'm so impressed that you can write perfect letters in the APOD! :clap: (And I agree that the picture does look a little bit like a man tending to his pet jellyfish...) :D

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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by orin stepanek » Wed May 19, 2021 11:59 am

:D Wow Ann you are fast! Oh BTW; I use paint to write like that!
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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by NCTom » Wed May 19, 2021 2:51 pm

Thanks for the annotation, Ann. It makes it so much more than just a beautiful and intriguing picture!

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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by Ann » Wed May 19, 2021 4:58 pm

NCTom wrote:
Wed May 19, 2021 2:51 pm
Thanks for the annotation, Ann. It makes it so much more than just a beautiful and intriguing picture!
Thanks, Tom! :D

But please, you math people out there. The blue star in the blue reflection nebula has a parallax of 0.5674 ± 0.0410 milliarcseconds.

How far away is it? Anyone?

Ann
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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by Chris Peterson » Wed May 19, 2021 5:23 pm

Ann wrote:
Wed May 19, 2021 4:58 pm
NCTom wrote:
Wed May 19, 2021 2:51 pm
Thanks for the annotation, Ann. It makes it so much more than just a beautiful and intriguing picture!
Thanks, Tom! :D

But please, you math people out there. The blue star in the blue reflection nebula has a parallax of 0.5674 ± 0.0410 milliarcseconds.

How far away is it? Anyone?
https://www.translatorscafe.com/unit-co ... -distance/ gives 5748 ly. Bookmark it.
Chris

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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by Judy » Wed May 19, 2021 6:43 pm

Are the orange and blue stars scattered across the background in more-or-less true color? So many of the photos on this site have colors added so we can see colors that human don't. I would love it if these were really blue and red.

Thanks! Love the picture.

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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by johnnydeep » Wed May 19, 2021 6:51 pm

Chris Peterson wrote:
Wed May 19, 2021 5:23 pm
Ann wrote:
Wed May 19, 2021 4:58 pm
NCTom wrote:
Wed May 19, 2021 2:51 pm
Thanks for the annotation, Ann. It makes it so much more than just a beautiful and intriguing picture!
Thanks, Tom! :D

But please, you math people out there. The blue star in the blue reflection nebula has a parallax of 0.5674 ± 0.0410 milliarcseconds.

How far away is it? Anyone?
https://www.translatorscafe.com/unit-co ... -distance/ gives 5748 ly. Bookmark it.
Except it's annoying that it doesn't include light years as an output distance. Not too hard to multiply by 3.26 I guess, but still.

The formula is actually really simple, as astronomical calculations go, but somehow I have a hard time remembering it: ly = 1000 / mas * 3.26
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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by Chris Peterson » Thu May 20, 2021 12:37 am

johnnydeep wrote:
Wed May 19, 2021 6:51 pm
Chris Peterson wrote:
Wed May 19, 2021 5:23 pm
Ann wrote:
Wed May 19, 2021 4:58 pm


Thanks, Tom! :D

But please, you math people out there. The blue star in the blue reflection nebula has a parallax of 0.5674 ± 0.0410 milliarcseconds.

How far away is it? Anyone?
https://www.translatorscafe.com/unit-co ... -distance/ gives 5748 ly. Bookmark it.
Except it's annoying that it doesn't include light years as an output distance. Not too hard to multiply by 3.26 I guess, but still.

The formula is actually really simple, as astronomical calculations go, but somehow I have a hard time remembering it: ly = 1000 / mas * 3.26
It always shows light years below the output box.
Chris

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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by Ann » Thu May 20, 2021 4:30 am

Chris Peterson wrote:
Wed May 19, 2021 5:23 pm
Ann wrote:
Wed May 19, 2021 4:58 pm
NCTom wrote:
Wed May 19, 2021 2:51 pm
Thanks for the annotation, Ann. It makes it so much more than just a beautiful and intriguing picture!
Thanks, Tom! :D

But please, you math people out there. The blue star in the blue reflection nebula has a parallax of 0.5674 ± 0.0410 milliarcseconds.

How far away is it? Anyone?
https://www.translatorscafe.com/unit-co ... -distance/ gives 5748 ly. Bookmark it.
Thanks, Chris! I tried it, and it really worked!

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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by Ann » Thu May 20, 2021 5:33 am

Judy wrote:
Wed May 19, 2021 6:43 pm
Are the orange and blue stars scattered across the background in more-or-less true color? So many of the photos on this site have colors added so we can see colors that human don't. I would love it if these were really blue and red.

Thanks! Love the picture.
Yes, I'd say that the colors are relatively true. The orange stars and Mars are a bit saturated. That is to say that if you were to look at them in the night sky, and even better, through a telescope, they would not look all that orange. But they would certainly look golden-yellow. You know what color Betelgeuse is, don't you? Next time you see Betelgeuse in the sky, try to memorize its color. Because Eta and Mu Gem are actually a little paler in color than Betelgeuse.

How do I know? It has to do with the star's B-V index, which measures the stars output in blue light versus its output in yellow-green light. The higher the B-V index, the redder is the star. The B-V index of Betelgeuse is around +2, but for Eta and Mu Gem, it is around +1.6. My impression is that a star's B-V index really really is a good indicator of its visual color.

It is much harder to see blue color than orange color in stars, because all blue stars are pale and close to white. That is because all blue also emit a lot of red and yellow light too, and they just emit even more blue light. Therefore their colors can never be intensely blue. Orange stars like Betelgeuse and Eta and Mu Gem, by contrast, emit almost no blue light at all, so their colors are very much more saturated, and their hues are easily visible.

What about the blue-looking stars in this picture?

The apparently bluest object is a star that "sits in a reflection nebula", which means that much of its blue light has been scattered around it by dust. The scattered light is very blue and shows up well in photographs, but we can't see it. It is too faint.


You know the Pleiades, don't you? The stars of the Pleiades normally look white when you look at them with the naked eye, but most people can see that they look bluish when they look at them through a telescope. But even through a telescope, you can't see the blue reflection nebulas, only the stars. It takes long-exposure photographs to bring out the nebulas.

But are the blue or bluish-looking stars in this picture really blue "IRL"? Yes, more or less. Some of the blue-looking stars in the picture are very very far away, and that goes for the star that sits in a blue reflection nebula. That star is some 5,700 light-years away! And there are a few other blue stars in the picture that are similarly far away. Then there are a few other bluish-looking stars that are much closer, some 500 light-years away.

The very distant blue stars look less blue than they really are, because there are so many minuscule cosmic dust particles between them and us that some of their blue light gets scattered away before it reaches us. That effect is called dust-reddening. Some of those distant stars are not only very bright but also intrinsically very blue, but we can't see it.

By contrast, there are some much more nearby stars that are intrinsically fainter and less blue, and they are far less affected by dust reddening. The bluest-looking star in the picture, at upper center-left, is a star of spectral class A2, with a B-V index of +0.02. The distance to this star is some 570 light-years. Actually a similarly blue-looking double star can be seen at far right, above right of Mars. The brightest component is a star of spectral class B9, whose B-V index may be -0.02. The distance to this star is some 1800 light-years.

So in general, you can trust the star colors in this image, even though you can't expect the stars to look the way they do here if you were to look at them with the naked eye (or even through a telescope). So what about planet Mars?

Mars is really strikingly reddish. That's why the ancients called planet Mars the god of war, because they thought that the planet was red with blood.

Ann
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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by johnnydeep » Thu May 20, 2021 11:46 am

Chris Peterson wrote:
Thu May 20, 2021 12:37 am
johnnydeep wrote:
Wed May 19, 2021 6:51 pm
Chris Peterson wrote:
Wed May 19, 2021 5:23 pm


https://www.translatorscafe.com/unit-co ... -distance/ gives 5748 ly. Bookmark it.
Except it's annoying that it doesn't include light years as an output distance. Not too hard to multiply by 3.26 I guess, but still.

The formula is actually really simple, as astronomical calculations go, but somehow I have a hard time remembering it: ly = 1000 / mas * 3.26
It always shows light years below the output box.
<smacks forehead>! There must be something about that screen design that's not up to the best GUI standards. Yeah, that's the ticket :ssmile: It's either that or I really need to get new glasses.
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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by Guest » Thu May 20, 2021 4:42 pm

Ann wrote:
Thu May 20, 2021 5:33 am
Judy wrote:
Wed May 19, 2021 6:43 pm
Are the orange and blue stars scattered across the background in more-or-less true color? So many of the photos on this site have colors added so we can see colors that human don't. I would love it if these were really blue and red.

Thanks! Love the picture.
Yes, I'd say that the colors are relatively true. The orange stars and Mars are a bit saturated. That is to say that if you were to look at them in the night sky, and even better, through a telescope, they would not look all that orange. But they would certainly look golden-yellow. You know what color Betelgeuse is, don't you? Next time you see Betelgeuse in the sky, try to memorize its color. Because Eta and Mu Gem are actually a little paler in color than Betelgeuse.

How do I know? It has to do with the star's B-V index, which measures the stars output in blue light versus its output in yellow-green light. The higher the B-V index, the redder is the star. The B-V index of Betelgeuse is around +2, but for Eta and Mu Gem, it is around +1.6. My impression is that a star's B-V index really really is a good indicator of its visual color.

It is much harder to see blue color than orange color in stars, because all blue stars are pale and close to white. That is because all blue also emit a lot of red and yellow light too, and they just emit even more blue light. Therefore their colors can never be intensely blue. Orange stars like Betelgeuse and Eta and Mu Gem, by contrast, emit almost no blue light at all, so their colors are very much more saturated, and their hues are easily visible.

What about the blue-looking stars in this picture?

The apparently bluest object is a star that "sits in a reflection nebula", which means that much of its blue light has been scattered around it by dust. The scattered light is very blue and shows up well in photographs, but we can't see it. It is too faint.


You know the Pleiades, don't you? The stars of the Pleiades normally look white when you look at them with the naked eye, but most people can see that they look bluish when they look at them through a telescope. But even through a telescope, you can't see the blue reflection nebulas, only the stars. It takes long-exposure photographs to bring out the nebulas.

But are the blue or bluish-looking stars in this picture really blue "IRL"? Yes, more or less. Some of the blue-looking stars in the picture are very very far away, and that goes for the star that sits in a blue reflection nebula. That star is some 5,700 light-years away! And there are a few other blue stars in the picture that are similarly far away. Then there are a few other bluish-looking stars that are much closer, some 500 light-years away.

The very distant blue stars look less blue than they really are, because there are so many minuscule cosmic dust particles between them and us that some of their blue light gets scattered away before it reaches us. That effect is called dust-reddening. Some of those distant stars are not only very bright but also intrinsically very blue, but we can't see it.

By contrast, there are some much more nearby stars that are intrinsically fainter and less blue, and they are far less affected by dust reddening. The bluest-looking star in the picture, at upper center-left, is a star of spectral class A2, with a B-V index of +0.02. The distance to this star is some 570 light-years. Actually a similarly blue-looking double star can be seen at far right, above right of Mars. The brightest component is a star of spectral class B9, whose B-V index may be -0.02. The distance to this star is some 1800 light-years.

So in general, you can trust the star colors in this image, even though you can't expect the stars to look the way they do here if you were to look at them with the naked eye (or even through a telescope). So what about planet Mars?

Mars is really strikingly reddish. That's why the ancients called planet Mars the god of war, because they thought that the planet was red with blood.

Ann

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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by VictorBorun » Sun May 23, 2021 2:21 am

I wonder how to make a Space Jellyfish like this?
Wiki says there is a foreground dark lane crossing the shell of supernova remnant;
it also says that the brighter half is now expanding at 80-100 km/s while the paler half is now slowed down to mere 30-40 km/s.

But where is that darkening matter? May it fill an equatorial disk in the shell?
And why does the slow and paler half have a larger radius?

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Re: APOD: The Jellyfish and Mars (2021 May 19)

Post by VictorBorun » Sun May 23, 2021 3:37 am

is Mars smeared because it was moving relatively to the stars?