SDSS used thousands of alumminum plates, just like the one your class has, to measure the spectrum of objects in the sky. Each hole on the plate represents the position of an object on the sky. SDSS astronomers measured the spectrum of many millions of objects: some are stars, some are galaxies and some are quasars.
Your plate has around 1000 holes in it (yes, really!), each corresponding to an object in the sky. Although all of these objects are bright enough to be seen using the SDSS telescope, you wouldn’t be able to see these with your naked eye – the constellations you are about to make were not within the reach of ancient cultures.
Step 1 – finding the brightest objects on your plate
In the same way that our ancestors chose the brightest objects in the sky to make pictures, we will choose the brightest objects in your plate. SDSS astronomers measured the magnitude of all objects in your plate, and have stored all of those numbers in a large set of tables, called a database. You will use a simple computer language called SQL to ask the database a question: which objects on my plate are the 20 brightest?
The following text does exactly that. Copy the text below, and paste it in the query window below.
select top 20 spa.ra, spa.dec, spa.dered_r as magnitude, spa.class, spa.z, soa.xfocal as x, soa.yfocal as yfrom specphotoAll as spajoin specObjAll as soa on soa.specObjID = spa.specObjIDwhere spa.plate = XXXXand spa.dered_r > 0order by spa.dered_r asc
Before you hit “Submit”, you will need to replace XXXX by the number of your plate. For example, if your plate is plate number 7616, then your query will look like
select top 20 spa.ra, spa.dec, spa.dered_r as magnitude, spa.class, spa.z, soa.xfocal as x, soa.yfocal as yfrom specphotoAll as spajoin specObjAll as soa on soa.specObjID = spa.specObjIDwhere spa.plate = 7616and spa.dered_r > 0order by spa.dered_r asc
When you’re ready, click “Submit”. The results will appear on the right-hand side. Then click “Download” to download your results to your local computer as a .csv file.
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Step 2 – Drawing your constellation
Next, we will use a spreadsheet to plot the positions of the 20 brightest objects of your plate. The example used here is done in Google Sheets, which requires a free Goggle Account, but you can use MS Excel, or any other software available to you.
Create a new Sheet, and import the csv file that you downloaded from this page (File->Import). You should see your data neatly arranged in a table. Select the last two columns, and make a s