SDSS used thousands of aluminum plates, just like the one your class has, to measure the spectrum of objects in the sky. Each hole on your plate represents the position of a star on the sky. SDSS astronomers measured the spectrum of many millions of stars in our galaxy.
Step 1 – finding the brightest stars on your plate
In the same way that our ancestors chose the brightest stars in the sky to make pictures, we will choose the brightest stars in your plate. SDSS astronomers measured the magnitude of all stars 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 stars on my plate are the 30 brightest?
The following text does exactly that:
select distinct top 30 star.ra, star.dec, PLATESCALE*(star.ra - plate.racen)/cos(plate.deccen*PI()/180.0) as x, PLATESCALE*(star.dec - plate.deccen) as y, obj.j as mag from apogeestar as star, apogeeObject as obj, apogeePlate as plate where obj.target_id=star.target_id and plate.location_id=star.location_id and plate.plate = XXXX order by mag
Get ready to find the brightest objects on your plate, using the SQL Search tool below.
- Click the Unlock button so you can enter your query into the search window
- Copy the text above and paste it into the “SQL Search” window below
- Replace the XXXX with your plate number (for example, if you have plate number 4951, enter 4951)
- Figure out whether your plate is a northern APOGEE plate or a southern APOGEE plate
- If it is a northern plate, the markings on the plate will be hand drawn; if it is a southern plate the markings will be printed onto the plate and there will be a large central hole (like the plate shown here Anatomy of a plate: APOGEE South)
- If you have a southern APOGEE plate, replace PLATESCALE with -328.589
- If you have a northern APOGEE plate, replace PLATESCALE with 217.7358 in the first line (… as x), and -217.7358 in the second line (… as y)
- Click Submit
- The 30 brightest objects on your plate will appear under Results to the right of the query window
- Click Download to save the results to your computer as a CSV (comma-separated value) file
Step 2 – Drawing your constellation
Next, we will use a spreadsheet to plot the positions of the 30 brightest stars 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 spreadsheet 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 X and Y columns and create a “Scatter Plot”. X and Y are the coordinates of the positions of each object on the plate, with the origin being located at the centre of the plate. You should get a plot like the one shown below.
Print the scatter graph you have created. Now, in groups or individually, imagine the points in your graph are stars on the sky, and imagine what they might represent. Draw your constellation, and write a short paragraph about what it means.
Step 3 – Showing your constellation on your plate
Finally, you will light up the stars of your constellation in your plate. The X and Y positions that you used are given in millimetres, and the centre of the plate corresponds to X=0 and Y=0. Using rulers and guidelines, find the holes that correspond to the 30 holes that you used for your constellation.
Instructions to help you find the holes on your plate that correspond to a given object can be found here : Locating objects on an APOGEE south plate.
How you light up your constellation is up to you! You can use Christmas lights, or bright reflecting stickers, or anything else! Use different colours for the different colored stars!
Display your plate to the rest of your school, together with all the drawings that different groups or people in your class designed based on the lit-up pattern on your plate. Your display should explain to others what the plate is, what constellations are, and what the different classes of objects are. Send us a photograph of your display!