Practice Using Aggregate Functions, Group By, and Order By
Write queries to answer the astronomy questions in Practice 7, 8, and 9.
Use the Schema
Browser when you need it.
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Practice 7. What are the northernmost and southernmost
objects with spectra contained in personal SkyServer?
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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 in run=1458, camcol=1?
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 or two
galaxies! Also, note that this query will probably take a long time to
execute. |
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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