Global Hands-On Universe meeting
July 15, 2007
Authentic Data in the Classroom with the Sloan Digital Sky Survey
Jordan Raddick (Johns Hopkins University)
Jordan Raddick
The Sloan Digital Sky Survey
• Map of the universe• 2.5 m telescope in
New Mexico• CCD imaging• Follow-up spectra
Jordan Raddick
The Data of the SDSS
Photometric Data
Spectral Data
Jordan Raddick
Photometric Data
• Tri-color images • Single-color FITS files
– ultraviolet (u)– green (g)– red (r)– infrared (i, z)
• Magnitudes through each filter
• Object type• More…
Jordan Raddick
Spectral Data
• 3800 to 9200 Ångstroms• GIF files with prominent
lines marked• FITS files available
– SpecView Java applet(STScI)
• Object type and redshift• Detailed line widths and strengths
Jordan Raddick
Introduction to DR6
• ~9,600 square degrees– (Full moon is 0.25 square degrees)
• Images of ~280 million objects– ~90 million stars, ~140 million galaxies
• ~1 million spectra– ~60,000 stars, 600,000 galaxies, 75,000 quasars
• Science quality data• Where in the sky?
Jordan Raddick
DR6 Photometric Coverage
(Both areas, Aitoff projection of equitorial coordinates)
Jordan Raddick
DR6 Spectral Coverage
(Both areas, Aitoff projection of equitorial coordinates)
Jordan Raddick
SkyServer web site
• Entire dataset from the SDSS
• Research-grade science data and tools
• Promotes use of real science data in education
Jordan Raddick
Example: H-R Diagram
• Strategy:– Get data for a lot of stars in a star cluster– Need magnitudes– Plot color vs. magnitude– Interpret
• Palomar 5– RA = 229.013, Dec = -0.123, Radius = 3 arcmin
Jordan Raddick
Get Data
• Search Form• Tools -> Search ->
Search Form• Form is a sentence
where you fill in words• “Show me stars
at RA = 229.013, dec = -0.1083, radius = 3. Show me 1,000. Get object ID, RA, Dec, and magnitudes.
• Click Generate Query
Jordan Raddick
Get Data
• Your request is translated into SQL code:select top 1000 p.objid, p.ra, p.dec, p.u, p.g, p.r, p.i, p.zfrom star p
• Switch Output Format to CSV• Click Submit Query to SkyServer or Submit
Query to Image List• Download or save file
Jordan Raddick
View and Analyze Data
• Open CSV file in a graphing program
• Note bug with Object IDs• Add new columns for
u-g, g-r, r-i, i-z
Jordan Raddick
Plot Data
Jordan Raddick
Interpret Plot
• Interpret plot to learn stellar evolution
• See SkyServer’s “Project” on H-RDiagram
• Projects -> Advanced ->H-R Diagram
Jordan Raddick
Galaxy Zoo
• New project• Classify galaxies
as spiral or elliptical
• Participate in meaningful scientific project