Doctor Science Knows

Wednesday, July 18, 2007

GalaxyZoo Tool Use

Use GalaxyZoo: don't just explore the world, explore the *Universe*!

So I ask for a galaxy, and at first all I saw was this:



"That's not a galaxy", says I. "I wonder what it really is?"

So I clicked through to the SkyServer Object Explorer page via the "Galaxy Ref:" link. Here I was disappointed to see the words, No scienceprimary SpecObj linked to this PhotoObj, which means they don't have a spectrum for the object and thus we don't know how far away it is. I then clicked on the image on that page, to get a bigger picture with the SDSS Finding Chart Tool:



Oh. I guess it is a galaxy, all right.

I wondered if some other part of this galaxy might have had its spectrum taken, so I went to the Navigate Tool, which is reachable both from the Object Explorer page (under PhotoObj on the left navigation bar) and from Finding Chart (as Navi, just below the DR6 logo).

On Navigate, the object you're looking at is outlined with a green box. One of the useful things to do here is to check the box under "Drawing options" for "Objects with spectra". When you do that, red boxes go around every object in the view for which there is spectroscopic data. This is extremely important, because the spectrum summary tells you (a) whether the object is really a galaxy at all, and (b) if so, how far away it is.

If there *is* a red spectrum box, you can click it in Navigator to select that object, then get to the new Object Explorer page by clicking "Explore" over the right.

In this case, I was surprised to find that there don't seem to be any parts of this galaxy with a spectrum (and thus distance), but since it takes up the most screen space of any galaxy I've stumbled upon yet, I assume it's pretty close by the standards of the universe.

I don't know (yet!) how to find out whether this galaxy has a NGC number or other "scientific name". I don't even know how to go from the RA/Dec parameters SDSS gives in degrees to the more usual hr:min:sec, so I can figure out what constellation this might be in. While I was exploring I noticed that there's a very bright, probably naked-eye-visible star to the South of this galaxy, at 190.417,-1.457, but I don't know how to convert that to more conventional coordinates, either. If you know, tell me!

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3 Comments:

  • 190.417,-1.457

    is 12h41m40s RA and -1 deg 27'25" Dec

    Just divide the RA in degrees by 360 and multiply by 24 to get hours. Then convert the decimal parts to minutes by multiplying by 60.

    By Blogger Ross Collins, at 3:05 PM  

  • Might be this galaxy: http://tinyurl.com/2w6dlg

    By Blogger Ross Collins, at 3:07 PM  

  • Hi,

    is NGC 4632 in Virgo.
    You can find a lot of information using the "search" NED SIMBAD or ADS in the left pane of the SDSS page. I found yours in SIMBAD...

    Also, why don't start a sort of "gallery" for trying to standardize the classification of those strange "blob" that sometimes GalaxyZoo is presenting?
    The tutorial present very obvious (well, after 2 o 3 hundreds...) examples, but in the reality, out there is a wild world indeed..

    By Blogger Paolo, at 11:23 PM  

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