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Perseus Cluster of Galaxies, green stars? (APOD 20 May 2008)
Posted: Tue May 20, 2008 1:59 pm
by orin stepanek
http://apod.nasa.gov/apod/ap080520.html
http://apod.nasa.gov/apod/ap030505.html
Nice view! Interesting mixture of two galaxies merging. When two galaxies merge does the two black holes tend to orbit each other and become the core of the combination? Seems as the concentration of stars in the combined galaxy would bring them closer together; or maybe the newly formed galaxy would just be larger!
Orin
Posted: Tue May 20, 2008 3:03 pm
by Animation
Which objects in the image are part of the Perseus cluster?
I know the small stars are in our galaxy.
I'm not sure about the circular shapes with the lens flare (or whatever that is) on them. Are they also stars in our galaxy that are close or that are aligned in such a way to make the "lens flare" or whatever? As an example, I'm talking about the bright blue flared object in the upper left.
Anyway, then there are the smudgy things. I can tell these are obviously galaxies, but which ones are part of the Perseus cluster? There are fuzzy/blobby galaxies, and more distinct spiral ones. Some seem "close" but some appear distant as if they probably arent in the cluster. For example there are a couple on the top of the image, one 40% from left and one about 35% rrom right, that look quite distant or unrelated to the other shapes.
This is one of those apod images I wish had been done with a mouse-over. If an astronomer could have circled the galaxies that ARE in the cluster with a red line, and circled the non-perseus ones with a blue line, and then digitally removed all the stars from our galaxy, such that a mouse-over would show you ... that would have ruled.
Lewis
Posted: Tue May 20, 2008 3:38 pm
by orin stepanek
The spiked ones (blue) are stars in the Milky-way; the gold globs are galaxies; than there are the spiral galaxies.
Orin
Posted: Wed May 21, 2008 10:20 am
by harry
G'day
Nice links Orin
Just imagine the full scope of what we can see. Over 100 billion galaxies with the tools at hand.
But! down under, in the land of ozzzz, we see them upside down.
Posted: Wed May 21, 2008 12:18 pm
by orin stepanek
harry wrote:G'day
Nice links Orin
Just imagine the full scope of what we can see. Over 100 billion galaxies with the tools at hand.
But! down under, in the land of ozzzz, we see them upside down.
Hey Harry! Depends on what you call upside down.
![Laughing :lol:](./images/smilies/icon_lol.gif)
Any more; up is away from and down is toward.
Orin
Removing the Milky Way
Posted: Wed May 21, 2008 1:20 pm
by CharlieNNC
Has anybody gone to the trouble of redoing this pic and others like it such as the Hubble Deep Field, and removing all the Milky Way stars so that you could get a view representative of being outside of this galaxy and looking out?
Posted: Wed May 21, 2008 2:00 pm
by BMAONE23
orin stepanek wrote:harry wrote:G'day
Nice links Orin
Just imagine the full scope of what we can see. Over 100 billion galaxies with the tools at hand.
But! down under, in the land of ozzzz, we see them upside down.
Hey Harry! Depends on what you call upside down.
![Laughing :lol:](./images/smilies/icon_lol.gif)
Any more; up is away from and down is toward.
Orin
![Wink :wink:](./images/smilies/icon_wink.gif)
Sometimes you just can"t tell about those South is Up people
G-day back atya
Green foreground stars in APOD 080520 (Perseus Cluster)
Posted: Wed May 21, 2008 11:04 pm
by crodom
Several of the foreground stars in the photo are green (have green halos). I'm familiar with the general explanation of why we do not see green stars. Are the green stars the result of too much green level in the composite?
Posted: Thu May 22, 2008 5:27 am
by NoelC
http://antwrp.gsfc.nasa.gov/apod/ap080520.html
I believe the colored halos around the bright stars to be an artifact from secondary filter reflections. In other words, light coming in bounces off the imager, up to the back side of whatever filter they used, then back down to the imager.
Assuming it's an image constructed from separate exposures taken through red, green, and blue filters, it looks as though the secondary reflections while the blue channel was being exposed were stronger than those from other channels, except for when the light was primarily yellow-red, causing strong secondary reflections in the red and green channels as well, which mixed with the stronger blue secondary reflections and yielded green.
It takes some effort, but secondary reflections can usually be mostly removed digitally.
I don't mean to be critical, but the data processing in that image leaves something to be desired. Things don't really look the way they are portrayed in there. Though the exposure appears to be quite deep, the black point has been clipped quite badly and the colors have been turned way up.
This is a more realistic looking image:
http://www.rc-astro.com/photo/id1156.html
-Noel
Posted: Thu May 22, 2008 8:41 am
by harry
G'day
That is why we won the Americas Cup with a down under thing.
But! that was a few years ago.
Re: Removing the Milky Way
Posted: Thu May 22, 2008 12:18 pm
by orin stepanek
CharlieNNC wrote:Has anybody gone to the trouble of redoing this pic and others like it such as the Hubble Deep Field, and removing all the Milky Way stars so that you could get a view representative of being outside of this galaxy and looking out?
I think I recall a picture where the frontal stars have been removed of blocked out. Maybe it can be found.
Orin
Posted: Thu May 22, 2008 1:13 pm
by orin stepanek
This is the one I remembered!
http://apod.nasa.gov/apod/ap050926.html
I don't recall any other ones though.
Orin
Posted: Thu May 22, 2008 1:21 pm
by Animation
Orin,
That is a cool pic with the stars removed, but its too bad there isnt one like it that is zoomed in so much. I wish the APOD image associated with this thread had a version with the stars removed. It'd be cool to see what percentage of the "specks" and "blobs" on the sky were actually galaxies. The "zoom" on the link you provided kinda took that aspect away since it was zoomed up as far as possible on the Virgo galaxies.
Lewis
Thanks Orin
Posted: Fri May 23, 2008 2:22 pm
by CharlieNNC
Yes, that is the idea, removing the Milky Way stars, and I agree with Animation that example is zoomed in too much. Would seem in this day of data processing, it would not be hard to ID and blank out our galaxy's stars, backfilling the space with something other than a black dot, to get a good idea of how it would look.
Charlie in NC