With our feet firmly planted on Earth and no telescope in sight, we can still look up at the night sky. All we have to do is turn in a small circle and we have taken in the entire sky. Almost everything we see with our unaided eyes is a star. Thousands of years ago people looked up at the sky, and they did one of the things humans do best: they looked for patterns. They imagined the outlines of shapes and they gave these shapes names. In this way, in many different cultures, at many different times, the constellations were created.
The system of northern hemisphere constellations that we most commonly use today came to us from the ancient Greeks. Constellations were one of the first ways that people communicated about the locations of objects in the sky. Today we still use these historic shapes to define broad areas of the sky. In this activity you will explore the concept of constellations and discover how they relate to the Sloan Digital Sky Survey images.
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 on-line 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 devise 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 Pre-Flight – Celestial Coordinates 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?