Practice Using Aggregate Functions, Group By, and Order By
Write queries to answer the astronomy questions in Practice 7, 8, and 9.
Use the Object
Browser when you need it.
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Practice 7. What are the limits in
right ascension of stripe 10?
Hint: This question takes some trickiness. First, look
at stripe 10 in the
Navigation Tool.
Get an idea of where the stripe is, then pick reasonable constraints for
the where block of your search.
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Practice 8. What is the redshift of the nearest galaxy
whose spectrum was measured by the SDSS with high (95%) confidence?
Use the equation
cz = H0d
to find the distance to the galaxy in light-years. The speed of
light, c, is 1 light-year per year. The constant H0, called
the Hubble constant, is about 70 km/s/Mpc, or
7.11 x 10-11 / yr.
Compare the distance you found to the distances to the Andromeda
Galaxy (2 million light-years) and the Whirlpool Galaxy (37 million
light-years). Does the distance you found seem reasonable? |
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Practice 9. What field has galaxies with
the highest average redshifts?
Be sure you are searching fields (as run-camcol-field) for
galaxies. Also look at how many spectrally measured galaxies
are in the field - make sure you don't pick a field with only one
galaxy! |
Each practice question can be answered in different ways, but
here are some
Sample Answers.
Notice that these practice questions have gotten more difficult, and
are more like the questions that astronomers really ask in their
research. You're getting better in your searches!
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