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.
Launch
the SQL search tool
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 tool
to find the data you want.
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. When you finish your analysis, E-mail us
your queries, your results, and your conclusions. We'll look over
all the results we receive, and we'll put the best of them up
on this web site!
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. |
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