Student Journals
Which Constellations are in the SDSS?
The Sloan Digital Sky Survey (SDSS) has captured images in over ¼ of the sky. Although there are over 340 million images of stars and galaxies in the SDSS there is still a lot of sky where the SDSS telescope has not pointed. Looking up at the sky, it is difficult to imagine how a 2.5 meter telescope sees the same view. In this activity we will use an online service called Astrometry.net to do just that. You can use your own images or ones that have been provided.
Let’s see how to do this with an example using an image taken by Vivian Hoette from the University of Chicago Yerkes Observatory in Williams Bay, Wisconsin.
Step 1: We start with an image Vivian took looking up at the constellation Taurus when the bright planet Jupiter was traveling through. You can follow these steps with any digital image of the night sky that is saved to your computer. If you would like to use one of the mystery images taken by SkyServer enthusiasts, click here. 
Step 2: Upload the image to Astrometry.net
Step 3: Wait up to 10 minutes. Refresh the web page every few minutes to see if the analysis is complete.
Step 4: When your results appear, click on the image to view the summary. You must mouse over the image to see additional options for viewing. Choose “annotated” to see the labels for constellations, bright stars and other well-known objects.
Step 5: The next really amazing part is that Astromentry.net can talk to the SDSS and show you where in your picture the SDSS has also captured images. Click the SDSS link in the image window to see this information.
These odd patterns are a result of many nights of imaging with a camera that has six columns of CCD chips. Can you see evidence of these six columns in the image above? The camera stays stationary as the sky moves across the recording device in long strips. It takes two runs, one slightly offset from the other, to produce a solid stripe. You can also see in the lower left the brightly colored strips that are the result of starlight from the bright star, Bellatrix, overwhelming the CCD chips.
Within the stripes, what do you observe about the stars as compared to the image taken with a regular camera?
Step 6: One additional tool Astrometry.net provides is a graphic that shows where in the sky you are looking. If you are looking at a large part of the sky as we see in Vivian’s image, Astronomy.net marks off the approximate boundaries of the image on a map on the right side of the page. This map flattens the dome of the sky out so you can see the whole thing at once. A few of the major lines of the celestial coordinates are marked. Below the image are tags for this image that communicate where the image originated and some of the brightest object it contains. See Preflight – RA and Dec for more help understanding these numbers.
Step 7: Last, go to the SkyServer Navigate tool. Use the information you received from Astrometry.net to move the Navigate window to some location within your original image. Can you find a star in Navigate that was identified by Astrometry? Record your observations. What does this reveal about the SDSS images? The SDSS telescope?
