Conclusion

Take another look at the query you used to get your first 1,000 quasars:

select top 1000

objid, modelmag_u, modelmag_g, modelmag_r, modelmag_i, modelmag_z,z

from
SpecPhoto

where
class='QSO'

The query you used limits the objects it returns by applying one “constraint” – the query returns only objects with zconf > .35. Zconf is a measure of the statistical confidence level in the redshift measurement. The query only returns quasars for which we are more than 35% certain that the measured redshift is correct.

Try modifying the query. A couple of ideas would be to change or eliminate the confidence level zconf, or to add a statement in the “where” clause to search for quasars less than a certain magnitude (such as u < 20). Or you could try searching for various lines in the quasars’ spectra.

To learn more about how to work with SQL, see SkyServer’s Searching for Data how-to tutorial.

When you are dealing with a large database such as the SDSS, you need to use tools such as the SQL Search form below to find the data you want.
[sqlsearchwp-casjobs num=”0″ default=”select top 1000 objid, modelmag_u, modelmag_g, modelmag_r, modelmag_i, modelmag_z,z from SpecPhoto where class=&#39QSO&#39″]

Research Challenge. Modify the query slightly to obtain a different set of data. For example, look at only quasars with poorly measured redshifts (set zconf < some number). Maybe you want to look at very red quasars by setting the i and z magnitudes larger than a certain number. You could also search for very blue quasars using a similar technique.

Think of a question about quasars that you want to answer, and modify the query to get the data that will let you answer that question. Analyze the data using a spreadsheet, then draw conclusions about the quasars.

If you need help with Structured Query Language, see SkyServer’s Searching for Data tutorial, or do a web search for SQL. For other tutorials on SQL, see here and here.