APOD: Mars in the Clouds (2016 Sep 08)

Comments and questions about the APOD on the main view screen.
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APOD: Mars in the Clouds (2016 Sep 08)

Post by APOD Robot » Thu Sep 08, 2016 4:06 am

Image Mars in the Clouds

Explanation: Wandering through this stunning field of view, Mars really is in front of these colorful cosmic clouds. The mosaic contructed from telescopic images is about 5 degrees (10 full moons) across. It captures the planet's position on August 26, over 7 light-minutes from Earth and very near the line-of-sight to bright star Antares and the Rho Ophiuchi cloud complex. In the exposure yellow-hued Mars, above and left, is almost matched by Antares, also known as Alpha Scorpii, below center. Globular star cluster M4 shines just right of Antares, but M4 lies some 7,000 light-years away compared to Antares' 500 light-year distance. Slightly closer than Antares, Rho Ophiuchi's bluish starlight is reflected by the dusty molecular clouds near the top of the frame.

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Ann
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Re: APOD: Mars in the Clouds (2016 Sep 08)

Post by Ann » Thu Sep 08, 2016 5:35 am

It's appropriate that Mars should be close to Antares, since the name of that mighty star, Antares, actually means "Rival of Mars".

Of course, when you consider the true nature of these two objects in the sky, they have almost nothing in common apart from their orange hue. Well... both are made of baryons, too.

Ann
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Guest

Re: APOD: Mars in the Clouds (2016 Sep 08)

Post by Guest » Thu Sep 08, 2016 8:06 am

I don't understand how a globular cluster stays together. The component stars must be orbiting around a constantly shifting center of mass and the orbits must be at all angles. So how is it that, as two stars pass close to each other, one or both are not ejected from the system?

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Ann
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Re: APOD: Mars in the Clouds (2016 Sep 08)

Post by Ann » Thu Sep 08, 2016 9:03 am

Guest wrote:I don't understand how a globular cluster stays together. The component stars must be orbiting around a constantly shifting center of mass and the orbits must be at all angles. So how is it that, as two stars pass close to each other, one or both are not ejected from the system?
Globulars are slowly dispersing. Lightweight stars get ejected more often than massive ones.

Ann
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Guest

Re: APOD: Mars in the Clouds (2016 Sep 08)

Post by Guest » Thu Sep 08, 2016 11:22 am

Ann wrote:
Guest wrote:I don't understand how a globular cluster stays together. The component stars must be orbiting around a constantly shifting center of mass and the orbits must be at all angles. So how is it that, as two stars pass close to each other, one or both are not ejected from the system?
Globulars are slowly dispersing. Lightweight stars get ejected more often than massive ones.

Ann
So I assume that the total mass of the cluster is insufficient to hold it together and that virtually all of the component stars are all on an outward spiral from the center of mass? Is that correct?

heehaw

Re: APOD: Mars in the Clouds (2016 Sep 08)

Post by heehaw » Thu Sep 08, 2016 11:29 am

Guest wrote:
Ann wrote:
Guest wrote:I don't understand how a globular cluster stays together. The component stars must be orbiting around a constantly shifting center of mass and the orbits must be at all angles. So how is it that, as two stars pass close to each other, one or both are not ejected from the system?
Globulars are slowly dispersing. Lightweight stars get ejected more often than massive ones.

Ann
So I assume that the total mass of the cluster is insufficient to hold it together and that virtually all of the component stars are all on an outward spiral from the center of mass? Is that correct?
Nope, not correct! The stars are all orbiting the center of mass of the cluster. As Ann pointed out, lighter stars are very very slowly ejected over billions of years. Globular clusters I find particularly interesting because they do NOT have dark-matter concentrations associated with them, unlike galaxies.

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Re: APOD: Mars in the Clouds (2016 Sep 08)

Post by Chris Peterson » Thu Sep 08, 2016 1:53 pm

heehaw wrote:Globular clusters I find particularly interesting because they do NOT have dark-matter concentrations associated with them, unlike galaxies.
So we believed until recently. However, it now appears that there is a population of globular clusters that do have very high dark matter concentrations. This further complicates our (already limited) understanding of the origin and evolution of globular clusters.
Chris

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Re: APOD: Mars in the Clouds (2016 Sep 08)

Post by Ann » Thu Sep 08, 2016 3:22 pm

Chris Peterson wrote:
heehaw wrote:Globular clusters I find particularly interesting because they do NOT have dark-matter concentrations associated with them, unlike galaxies.
So we believed until recently. However, it now appears that there is a population of globular clusters that do have very high dark matter concentrations. This further complicates our (already limited) understanding of the origin and evolution of globular clusters.
Cen A. Dark matter globulars are marked in red. Normal globulars
are marked in blue and dwarf galaxy-like clusters are green.
Credit: ESO/Digitized Sky Survey. Acknowledgement: Davide de Martin.
Yes, dark matter globulars have been detected in Cen A, NGC 5128. But Cen A is a very strange galaxy, where a massive galactic merger is in progress, and the central black hole of the elliptical galactic component is quite active.

Perhaps the dark matter globulars owe at least some of their strange properties to the strange properties of their parent galaxy (galaxies)?

Ann
Last edited by Ann on Thu Sep 08, 2016 10:10 pm, edited 1 time in total.
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Re: APOD: Mars in the Clouds (2016 Sep 08)

Post by Jim Armstrong » Thu Sep 08, 2016 4:27 pm

I had to read the caption a few times and look at the picture a few more to be sure which object is Mars.
I expect my telescopic views of planets to have a discrete edge, not the diffuse, star like, one shown here.
What am I missing?

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Re: APOD: Mars in the Clouds (2016 Sep 08)

Post by Chris Peterson » Thu Sep 08, 2016 4:40 pm

Jim Armstrong wrote:I had to read the caption a few times and look at the picture a few more to be sure which object is Mars.
I expect my telescopic views of planets to have a discrete edge, not the diffuse, star like, one shown here.
What am I missing?
You're looking at an image that is 5.5° on a side. The image scale is 10.5 arcseconds/pixel. Mars itself currently has an apparent size of 10 arcseconds. So at the scale of this image, it is about 1 pixel across. In other words, it is unresolved, just like the stars, and optically indistinguishable from a star- a point source. Like all optical point sources, its apparent diameter in the image is determined only by its brightness.
Chris

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Re: APOD: Mars in the Clouds (2016 Sep 08)

Post by Fred the Cat » Thu Sep 08, 2016 6:52 pm

Jim Armstrong wrote:I had to read the caption a few times and look at the picture a few more to be sure which object is Mars.
I expect my telescopic views of planets to have a discrete edge, not the diffuse, star like, one shown here.
What am I missing?
It's interesting seeing similar images without Mars.
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heehaw

Re: APOD: Mars in the Clouds (2016 Sep 08)

Post by heehaw » Thu Sep 08, 2016 8:42 pm

Thanks a million for the dark-matter-in-globulars reference! Fascinating!

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Re: APOD: Mars in the Clouds (2016 Sep 08)

Post by MarkBour » Thu Sep 08, 2016 11:21 pm

Chris Peterson wrote:it now appears that there is a population of globular clusters that do have very high dark matter concentrations. This further complicates our (already limited) understanding of the origin and evolution of globular clusters.
Fascinating. I wonder if globular clusters "create" dark matter, or vice versa (or both).
Mark Goldfain

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Re: APOD: Mars in the Clouds (2016 Sep 08)

Post by Ann » Fri Sep 09, 2016 12:35 am

MarkBour wrote:
Chris Peterson wrote:it now appears that there is a population of globular clusters that do have very high dark matter concentrations. This further complicates our (already limited) understanding of the origin and evolution of globular clusters.
Fascinating. I wonder if globular clusters "create" dark matter, or vice versa (or both).
I think we can rule out any possibility that globular clusters create dark matter.

Large concentrations of dark matter, however, attracts baryonic matter (the stuff that you, me and the stars in globular clusters are made of).

However, there is evidence that dark matter can separate from baryonic matter.

I'm thinking of the fact that most globulars are found in the halos of galaxies. If they were not born there, they might have been "flung" there (due to galactic interactions, for example). Perhaps many globulars shed dark matter that way? Perhaps they were born with dark matter, but lost it over billions of years? On the other hand, perhaps some globulars can collide with discrete clumps of dark matter during titanic collisions and get merged with it, when everything is flying this way and that?

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Re: APOD: Mars in the Clouds (2016 Sep 08)

Post by DavidLeodis » Fri Sep 09, 2016 2:08 pm

Fred the Cat wrote:
Jim Armstrong wrote:I had to read the caption a few times and look at the picture a few more to be sure which object is Mars.
I expect my telescopic views of planets to have a discrete edge, not the diffuse, star like, one shown here.
What am I missing?
It's interesting seeing similar images without Mars.
This is a link to an image in Sebastian Voltmer's website without Mars:- http://www.astrofilm.com/bestof/pics/en ... i_SSO.html

It was taken in October 2014 and the extreme similarity to the APOD image (apart from the absence of Mars) does surprise me. Though I hope it has not been done it could be as if Mars has been superimposed onto that image.

Edit added a few hours later: I've now found that Sebastian's website has a link to his section in the image hosting Flickr website which has the APOD image. In its information it states "MARS & Rho Ophiuchi - Aug 26, 2016...Exposures: Main frame with Mars: L-RGB 4x180sec. Outer field/border: data from a previous 6-panel mosaic (each 4x180sec)".