Using Data from the Sloan Digital Sky Survey

1
Using Data from the SloanDigital Sky Survey In
the Classroom
Jordan Raddick (Johns Hopkins University)
Visualization of Astrophysical Data
workshopKavli Institute for Cosmological
Physics May 25, 2005
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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

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The Telescope

• 2.5 meter F/5 reflector
• Very wide (3 degree) field of view
• Alt-az mount
• Drift scanning

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The Spectrographs

• Two fiber-fed spectrographs
• Each can record 320 spectra simultaneously(640
  total)
• Determine redshifts, spectral types, chemical
  compositions

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The Data of the SDSS
Photometric Data
Spectroscopic Data
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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

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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

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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

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Introduction to SkyServer

• Data Release 3 (DR3)
• SkyServer
• http//skyserver.sdss.org

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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?

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DR3 Imaging Coverage
(Aitoff projection of equitorial coordinates)
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DR3 Spectral Coverage
(Aitoff projection of equitorial coordinates)
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SkyServer

• A public interface toSDSS data
• Servers donated byHewlett-Packard
• Software, expertisedonated by Microsoft
• Jim Gray, Curtis Wong

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SkyServer

• Funds from
• NSF
• STSci (IDEAS grant)
• Maryland Space Grant
• First light 6/4/2001

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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

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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

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Example Navigation tool
Main windowDisplays images
Data
Change RA/Dec
Closeup
DisplayOptions
Controls
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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)

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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

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Scavenger Hunt Teacher Notes

• Lesson Plan
• Goals
• Prerequisites
• Vocabulary
• Procedure
• Background reading
• Assessment
• Sample solutions (password protected)
• Rubrics

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Scavenger Hunt Teacher Notes

• Correlated to Teaching Standards
• National Science Education Standards
• AAAS Project 2061
• NCTM (Mathematics)
• NETS Indicators (Technology Ed)

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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

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Contact Information

• Jordan Raddick(410) 516-8889raddick_at_pha.jhu.edu
  
• http//skyserver.sdss.org

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The rest of this presentation

• Is adapted from a SkyServer workshop from an AAPT
  meeting
• Gives more detail about how to use SkyServer

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Retrieving Data with SkyServer

1. Navigation Tool
2. Explore Tool
3. Get Spectra and Get Plates

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Navigation Tool

• Pan and zoom through the sky
• Click on star/galaxy for summary of photo data
• Online notebook to save objects
• Create telescope finding charts

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Navigation Tool
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Object Explorer

• Information on single objects
• Photometric and spectroscopic
• Look up by object ID, position,
• Correlations to data from other sky surveys

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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 0.5arcminutes
• Navigate link to Navigation tool
• FITS download raw images (FITS)

continued
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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
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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

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Getting Raw Images from Object Explorer

• Click PhotoObj -gt FITS
• Corrected Frames are final images
• One-wavelength, black/white
• Zipped files
• Extension .fts.gz
• Use WinZip to extract single .fts file

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Searching the Data

1. Radial Search
2. Rectangular Search
3. SQL Search
4. Schema Browser
5. Image List

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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 limit

continued
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Radial Search

• Example search for Objects in galaxy cluster
  Abell 168 (from Famous Places)

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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

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Rectangular Search

• Similar to radial search
• Search area is a rectangular box

continued
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Rectangular Search

• Example Search for objects near Abell 0957
• Select CSV for format

continued
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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
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Rectangular Search

• To open a .csv file
• Use Excels Text Import
• Wizard
• Open Excel
• From the Data menu,select Get External Data
  -gtImport Text File

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Rectangular Search

• Select Delimited, then Comma
• Change anyobjid columns toText
• This preservesall 18 digits of Object IDs

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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
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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

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How to Learn SQL

• Go to Help -gt How-To -gt Searching for Data
• Interactive tutorial on SQL

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Image List tool

• Go to Tools -gt Visual Tools -gt Image List
• Click Use query to fill form
• Enter query andclick Submit

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Image List tool

• Results appear in window
• Click Send toList

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Image List tool

• Thumbnail for each queryresult
• Click any thumbnail to goto Navigation tool

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Example Stellar Evolution

• Adapted from Projects -gt Advanced -gt H-R Diagram
• How do stars change over time?
• You cant watch a star age
• Stars live for billions of years!
• So how can you learn?

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Example Stellar Evolution

• Solution study lots of stars
• Large statistical sample
• Stars at all stages of life
• What properties to observe?
• Temperature
• Luminosity (brightness)

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Temperature and Color

• Stars emit thermal (blackbody) radiation
• Hotter stars have ashorter peak wavelength
• Shorter wavelength bluer
• How do you quantify blueness?

A star with temperature 4000 K peak
wavelength in blue
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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

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Temperature and Color

• Difference in magnitudes is color
• Astronomical definition
• Color is a stand-in for temperature

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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)

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Luminosity and Magnitude

• Problem
• If you see a faint star, how do you know if its
  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

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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

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The H-R Diagram

• 4 groups
• 1) Main sequence
• Like the Sun
• Center of graph
• More mass-ive stars on left top

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The H-R Diagram

• 2) Red giants
• Middle right
• Older stars
• 3) Super- giants
• Horizontal branch at top
• Older, more massive stars

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The H-R Diagram

• 4) White dwarfs
• Bottom left
• Very old, small, cool

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The H-R Diagram

• H-R diagram maps stellar evolution
• Main sequence -gt Red Giant / Supergiant -gt White
  Dwarf (for stars lt 5-ish Solar Mass)
• Explained by physics of fusion

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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

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Pal 5 from the Palomar Sky Survey
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Pal 5 from the SDSS
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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

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Sample H-R Diagram
Yours will probably look different!
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An Easier H-R Diagram

• Wasnt 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)

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H-R Diagram of Palomar 5
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H-R Diagrams Side-by-side
From images
From query
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Interpreting the H-R Diagram

• See the
• Main sequence
• Red giants
• Horizontalbranch (supergiants)
• White dwarfs too faint
• Where are big main sequence stars???

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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?

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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

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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

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Interpreting the H-R Diagram

• But, youve learned something valuable
• Cluster is a few billion years old
• (not millions or 100s of billions)
• And, youve done real science!
• Same data professionals use
• Similar analysis
• Valuable conclusions
• Can you think of extensions?
• Could be good science fair projects

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VII. Student Projects with SDSS Data

• A. Projects on SkyServer
• Examples of Student Lessons
• Create Your Own (Research!)

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SkyServer Projects

• We have class-ready lesson plans online
• SkyServer projects
• All that you did today wereadaptedProjects!

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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
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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 Standards

continued
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Teachers Guides

• Go to Projects main page (Ill show you)
• Click Register as a SkyServer teacher
• Fill out form
• If you forget school address, make one up
• You can update later
• We dont verify with your school we just say
  that to scare your students
• Tomorrow, you will be able to access sample
  solutions

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Teachers Guides

• Click on See the Teachers Guides
• Look through teachers guides
• Many projects are long, but you can do parts of
  them
• For example, Thermal Radiation Curves in the
  Color projects

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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 skys the limit!
• Additional resources on CD
• Let us know what you do!

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Formal Evaluation

• We are beginning evaluation program
• Tell me what projects you will use
• Ill send you copies of
• Student/teacher surveys
• Pre/post-tests
• Ill include postage mail them back
• 7 classes so far results look good, but we need
  more data!
• Let me know if you can help

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Youve been a great audience!

• Let us know how you use SkyServer
• Send comments and suggestions
• Looking for test classes
• Surveys and pre/post-tests
• Well send you free SDSS stuff
• Jordan Raddick
• [phone]
• raddick_at_pha.jhu.edu