Using SkyServer separately
I have been looking at M87, and there is a globular cluster receding from it, called HVGC-1. See. http://en.wikipedia.org/wiki/HVGC-1
The wiki article gives the RA and dec.
If I go to http://skyserver.sdss.org/dr12/en/tools/chart/navi.aspx
and plug in the values, I get a direct hit. http://skyserver.sdss.org/dr12/en/tools/chart/navi.aspx?ra=187.72788241976&dec=12.6829510786482&scale=0.2
However, M87 does not appear. So I use the minus sign to scale out, and it will show. But when I click on M87, it says "no objecs have been found within 0.2 arcminutes" and I cannot access any information. And I tried recentering, and then going in, but gave the same message.
Is there a way to make this work as well as SkyServer does in Galaxy Zoo?
Sometime in the evolution of SDSS, the core team discovered that near extended, bright objects they could not get consistent, accurate photometry from the camera. So, after this, data releases 'masked out' such regions. M87 is a classic example of such a region.
You may still 'find' such objects if you use the DR7 Navigate tool (here centered on a nice, 'pure white', galaxy) rather than DR8, DR9, ... DR12's.
The old GZ forum has an article on this, "There's a hole in the sky (several actually)", including some comments from two of the SDSS core team.
Hope this helps.