Random Objects Tutorial
The SDSS catalog database is about a terabyte (1,000,000 MB) - far too big to download and work with all at once. But you can get a random subset of the data using an SQL Search. To learn more about SQL, see SkyServer's SQL Tutorial and guide to Using SQL with SkyServer.
- Go to the SQL Search page. You can also access this page from the astronomers' main page, look under Search Tools. From the public main page, look under SkyServer Tools, then Search.
- In the large textbox, type the following SQL query:
SELECT u, g, r, i, z FROM Galaxy WHERE htmid*37 & 0x000000000000FFFF < (650 * 0.001)
- The query will return a 0.001% subset of the data. To return a different percentage subset of the data, change the final 0.001 to a different number (for example, for a random 0.5% subset of the data, change it to 0.5).
- The query will return the magnitudes of a 0.001% subset of the data. You can also return other data, such as positions and object IDs.
For more details on how this query works, see Data Subsample Query on SkyServer.