using data from the sloan digital sky survey in the classroom jordan raddick (johns hopkins...
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Using Data from the SloanDigital Sky SurveyIn the Classroom
Jordan Raddick (Johns Hopkins University)
Visualization of Astrophysical Data workshopKavli Institute for Cosmological Physics
May 25, 2005
Goals of the SDSS
• Map sky down from ~9th to ~23rd magnitude
• Images in 5 color bands form 3800Å to 9200Å
• Obtain spectra for 1 million galaxies and 100,000 quasars
• Create a detailed 3Dmap of the universe
The Telescope
• 2.5 meter F/5 reflector
• Very wide (~3 degree) field of view
• Alt-az mount
• Drift scanning
The Spectrographs
• Two fiber-fed spectrographs
• Each can record 320 spectra simultaneously(640 total)
• Determine redshifts, spectral types, chemical compositions
Photometric Data
• Tri-color images (g-r-i images)• FITS files (single-wavelength B/W images)• Magnitudes through each filter• Object type (star or galaxy)• Status (i.e. good seeing, cosmic rays, etc.)• Flags (i.e. saturated pixels, moving object,
etc)• Photometric redshifts
Spectral Data
• Moderate resolution (~1.3 Angstroms/pixel) from 3800 to 9200 Angstroms
• GIF files with prominent lines marked
• FITS files available
• Detailed line widths and strengths
Online Access to the Data
• All data will be made available online, free
• New data added in six chunks
• Currently Data Release 3– Released October 2004
Introduction to SkyServer
• Data Release 3 (DR3)
• SkyServer
• http://skyserver.sdss.org
Introduction to DR3
• ~5,200 square degrees– (Full moon is 0.25 square degrees)
• Images of ~140 million objects– ~60 million stars
• ~350,000 spectra– ~46,000 quasar spectra
• Science quality data
• Where in the sky?
SkyServer
• A public interface toSDSS data
• Servers donated byHewlett-Packard
• Software, expertisedonated by Microsoft– Jim Gray, Curtis Wong
Goals for SkyServer
• Make high-quality astronomy data available to everyone– Create easy-to-use tools to access data
• Allow amateurs to conduct professional-quality research
• Promote the use of real science data in the classroom
SkyServer Tools
• Simple tools for accessing data
• Focus often on single objects
• Prioritize information – First listed should be most important
• Most tools are web service-based– Work should be done on server
• Most written by A. Szalay et al at JHU
Example: Navigation tool
Main window:Displays images
Data
Closeup
Change RA/Dec
DisplayOptions
Controls
SkyServer Projects
• Make the data useful in formal ed settings
• Teach specific topics, tied to curriculum– Broader than just astronomy (e.g. spectra in
chemistry)
• Need clear logic for student to follow
• Make it as easy as possible for teachers
• Written by J. Raddick (science writer) and R. Sparks (high school teacher)
Example: Scavenger Hunt
• Students go on a scavenger hunt of sky
• Find stars, galaxies,quasars, meteor trails
• Look for specificmagnitudes
• Introduces students to SkyServer tools
• Teaches night sky objects, quantitative reasoning
Scavenger Hunt Teacher Notes
• Lesson Plan– Goals– Prerequisites– Vocabulary– Procedure
• Background reading
• Assessment– Sample solutions (password protected)– Rubrics
Scavenger Hunt Teacher Notes
• Correlated to Teaching Standards– National Science Education Standards– AAAS Project 2061– NCTM (Mathematics)– NETS Indicators (Technology Ed)
Current & Future Work
• Combining SkyServer with other projects– Hands-On Universe for follow-up observations– NU Collaboratory for online mentoring and
collaboration
• Apply same design methods to National Virtual Observatory (NVO) education
The rest of this presentation…
• Is adapted from a SkyServer workshop from an AAPT meeting
• Gives more detail about how to use SkyServer
• Pan and zoom through the sky
• Click on star/galaxy for summary of photo data
• Online notebook to save objects
• Create telescope finding charts
Navigation Tool
• Information on single objects– Photometric and
spectroscopic
• Look up by object ID, position,
• Correlations to data from other sky surveys
Object Explorer
Object Explorer• Search by – various methods to search for
objects (ID, RA/Dec, Spectrum Nos.)• Summary – general photo and spectral info• PhotoObj – photometric data• Field – statistical data for a region of sky• Frame – JPEG images and their
parameters• PhotoZ – photometric redshifts• Neighbors – list of objects within 0.5
arcminutes• Navigate – link to Navigation tool• FITS – download raw images (FITS)
continued
Object Explorer• SpecObj – measured parameters for a
spectrum• SpecLine – information on individual lines• SpecLineIndex – line intensities used to
find properties of galaxies• XCRedShift – Cross-correlation redshifts• ELRedShift – emission line redshifts• Spectrum – GIF of spectrum• Plate – information on plate that contains
the spectrum• FITS – raw (FITS) file of the spectrum
continued
Object Explorer• NED Search – searches for object in
NASA Extragalactic Database (NED)
• Virtual Sky – searches data at www.virtualsky.org
• Save in Notes – saves object to online notebook
• Show Notes – Shows objects in your notebook
• Print Page – prints the current display
Getting Raw Images from Object Explorer
• Click “PhotoObj -> FITS”
• “Corrected Frames” are final images
• One-wavelength, black/white
• Zipped files– Extension .fts.gz– Use WinZip to extract single .fts file
Searching the Data
A. Radial Search
B. Rectangular Search
C. SQL Search
D. Schema Browser
E. Image List
Radial Search
• Search around specified coordinates• Input ra, dec, radius• Can apply magnitude cuts for all five filters
(optional)• Can retrieve data in HTML, XML, or CSV
files– CSV files can be opened by most
spreadsheet programs
• 1,000 object limitcontinued
Notes About the Results• ObjID, run, rerun, camcol, field and obj can be
used to look up data in the Object Explorer or Get Fields
• Obj Type: 3 = galaxy, 6 = star• Err_u, etc, are uncertainties in magnitudes
Rectangular Search (cont)
• To save as a .csv file– Click the File
menu and select “Save As”
– Click “Save as type” and select text
– Type a file name such as Abell0957.csv
– Click Save
continued
Rectangular Search
To open a .csv fileUse Excel’s “Text
ImportWizard”• Open Excel• From the Data
menu,select Get External Data ->Import Text File
Rectangular Search
• Select “Delimited,” then “Comma”
• Change anyobjid columns to“Text”
• This preservesall 18 digits of Object IDs
SQL Search
• What if you want to search for specific objects in the database?
• Example: show me all bright blue galaxies
• Database can return all bright blue galaxies and only bright blue galaxies!
• How? SQL!
• Incredibly powerful and flexible interface
continued
SQL Search
• SQL – Structured Query Language– Common database access language– Industry standard, so students have practical
advantages to learning
• Allows advanced searches (“queries”) of data
• Search using constraints on any variable
• Return any or all types of data
Image List tool
• Go to Tools -> Visual Tools -> Image List
• Click “Use query to fill form”
• Enter query andclick Submit
Example: Stellar Evolution
• Adapted from Projects -> Advanced -> H-R Diagram
• How do stars change over time?
• You can’t watch a star age– Stars live for billions of years!
• So how can you learn?
Example: Stellar Evolution
• Solution: study lots of stars– Large statistical sample– Stars at all stages of life
• What properties to observe?– Temperature– Luminosity (brightness)
Temperature and Color
• Stars emit thermal (“blackbody”) radiation– Hotter stars have a
shorter peak wavelength– Shorter wavelength =
bluer
• How do you quantify “blueness”?
A star with temperature 4000 K [peak wavelength in blue]
Temperature and Color
• Take picture of star in two filters– Such as g and r
• Ratio of bright-nesses shows up
• Magnitude islogarithmic, so take difference inmagnitudes– Such as g-r
Temperature and Color
• Difference in magnitudes is “color”– Astronomical definition
• Color is a stand-in for temperature
Luminosity and Magnitude
• Luminosity: how much light the star emits
• [Apparent] Magnitude: how much light gets to Earth– Measured in specific wavelength– Logarithmic scale– Backwards (brighter stars,
lower magnitudes)– Depends on distance (farther
stars tend to look fainter)
Luminosity and Magnitude
• Problem– If you see a faint star, how do
you know if it’s really faint, or just far away?
• Solution– Look at star clusters– Nearly same distance from Earth, so…– Faint cluster stars really are faint– Magnitude can substitute for luminosity
The H-R Diagram
• Temperature vs. luminosity is “H-R Diagram”– After discoverers, Hertzsprung and Russell– Temp on x-axis, luminosity on y– For us, color on x-axis, magnitude on y
The H-R Diagram
• 4 groups:
• 1) Main sequence– Like the Sun– Center of
graph– More mass-
ive stars on left top
The H-R Diagram
• 2) Red giants – Middle right– Older stars
• 3) Super- giants– “Horizontal
branch” at top
– Older, more massive stars
The H-R Diagram
• H-R diagram maps stellar evolution– Main sequence -> Red Giant / Supergiant ->
White Dwarf (for stars < 5-ish Solar Mass)
• Explained by physics of fusion
Our Star Cluster: Palomar 5
• Globular cluster – old star cluster just outside our galaxy
• Famous cluster Palomar 5 (“Pal 5”)
• Discovered in 1950s by Palomar Observatory Sky Survey (POSS)– Palomar Observatory near San Diego– Biggest optical sky survey until SDSS
Palomar 5 Activity
• Open the Navigation tool
• Go to Palomar 5 coordinates– RA = 229.013 ; Dec = -0.123
• Click on 10-15 stars– Bright and faint
• Record g and r magnitudes
• Graph g-r (x-axis) vs. r (y-axis)
• Take about 15 minutes to do this
Sample H-R DiagramH-R Diagram of Palomar 5
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0 0.2 0.4 0.6 0.8 1
g-r
r
Yours will probably look different!
An Easier H-R Diagram
• Wasn’t that hard and labor-intensive?
• Easier way: SQL!!!!
• Open SQL Search tool
• Write a query– Hint: did you learn the function
fGetNearbyObjEQ() ?
• Save results, open in Excel
• Make a new H-R Diagram (g-r vs. r)
H-R Diagrams Side-by-sideH-R Diagram of Palomar 5
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0 0.2 0.4 0.6 0.8 1
g-r
r
H-R Diagram
1415161718192021222324
0 0.2 0.4 0.6 0.8 1
g-rr
From images
From query
Interpreting the H-R Diagram
• See the:– Main
sequence– Red giants– Horizontal
branch (supergiants)
– White dwarfs too faint
• Where are big main sequence stars???
H-R Diagram
1415161718192021222324
0 0.2 0.4 0.6 0.8 1
g-r
r
Interpreting the H-R Diagram
• They burned out their fuel and became red giants!
• “Turnoff” frommain seqtells you age of cluster
• So how old is Palomar 5?
H-R Diagram
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0 0.2 0.4 0.6 0.8 1
g-r
r
Interpreting the H-R Diagram
• Hard to tell
• Where is turnoff?
• Somewherebetween g-r = 0.25 and 0.4
• Leads to an age of 1-5 billion years– See palomar5.doc to learn why
Interpreting the H-R Diagram
• Recent (Jan. 2003) age estimate for Palomar 5– 10-12 billion years– From Hubble data
• Why the difference?– Large data scatter– Foreground/background stars?– H-R is one of many age techniques
Interpreting the H-R Diagram
• But, you’ve learned something valuable– Cluster is a few billion years old– (not millions or 100s of billions)
• And, you’ve done real science!– Same data professionals use– Similar analysis– Valuable conclusions
• Can you think of extensions?– Could be good science fair projects
VII. Student Projects with SDSS Data
A. Projects on SkyServer
B. Examples of Student Lessons
C. Create Your Own (Research!)
SkyServer Projects
• We have class-ready lesson plans online– SkyServer
projects– All that you
did today were[adapted]Projects!
SkyServer Projects
• Under “Projects” link of main page
• All projects use SDSS data extensively
• Most projects use inquiry-based learning
• Student activities– Questions – Exercises
continued
SkyServer Projects
• Teachers’ Guides for all projects
• Goals, background knowledge, structure
• Advice on leading class through project
• Sample solutions and rubrics
• Correlations to standards– AAAS Project 2061– NCTM Principles
and Standardscontinued
Teacher’s Guides
• Go to Projects main page (I’ll show you)
• Click “Register as a SkyServer teacher”
• Fill out form– If you forget school address, make one up– You can update later– We don’t verify with your school… we just say
that to scare your students
• Tomorrow, you will be able to access sample solutions
Teacher’s Guides
• Click on “See the Teacher’s Guides”
• Look through teacher’s guides
• Many projects are long, but you can do parts of them– For example, Thermal Radiation Curves in the
Color projects
Create Your Own Projects
• Now you know how to use the site• Appropriate topics might include: galaxy
classification, asteroids, large-scale structure, spectroscopy, the Hubble Diagram, Image processing, Colors, Spectral Types of Stars and many others
• Be creative – the sky’s the limit!• Additional resources on CD• Let us know what you do!
Formal Evaluation
• We are beginning evaluation program
• Tell me what projects you will use
• I’ll send you copies of– Student/teacher surveys– Pre/post-tests
• I’ll include postage – mail them back
• 7 classes so far… results look good, but we need more data!
• Let me know if you can help
You’ve been a great audience!
• Let us know how you use SkyServer
• Send comments and suggestions
• Looking for test classes– Surveys and pre/post-tests– We’ll send you free
SDSS stuff
• Jordan Raddick– (410) 516-8889– [email protected]