Using SDSS Navigator

Let's look at the properties of Abell 2065. The cluster's sky position is

(RA,Dec) = (230.62156, +27.70763)

where both coordinates are given in decimal degrees.

Go to SDSS Skyserver: http://skyserver.sdss.org/dr16/ and click on Navigate (under Data Access).

Go to Navigate, and put in the cluster coordinates. Click "Search". Hopefully you'll see a cluster.

If you click on "Grid" (in Drawing Options), you'll get a scale bar which helps you work out the angular scale of the image. You can zoom in and out using the magnifying class +/- buttons, and you can pan by click-dragging.

Note: Clicking "Invert Image" often helps you see things better.

Click on a galaxy. Over to the right, you'll see the galaxy in a little zoomed-in window, with the ugriz magnitudes given above it. If you click the "Explore" button underneath the zoom window, a new webpage will open up with more detailed properties of the galaxy, including (if it exists) a spectrum.

If you go back to the Navigate page, and (under Drawing Options) click "Objects with Spectra", it will highlight all sources that have spectroscopy, and you can click on one of them, click on Explore again, and you will see both photometry and spectroscopy data.

Play around. Scroll, zoom, click on galaxies and hit "Explore", etc. Look at a few spectra of galaxies in the field. Work out the following:

Roughly how big (in arcminutes) is the cluster?
What is a rough guess for the redshift of the cluster?
Find a background quasar and look at its spectrum

VERY IMPORTANT: When Navigate says an object has type = STAR, that does not mean it is actually a star. It only means that it is an unresolved point source. It might be a star, but it could also be a small, unresolved galaxy.