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

The Data of the SDSS

Photometric Data

Spectroscopic Data

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?

DR3 Imaging Coverage

(Aitoff projection of equitorial coordinates)

DR3 Spectral Coverage

(Aitoff projection of equitorial coordinates)

SkyServer

• A public interface toSDSS data

• Servers donated byHewlett-Packard

• Software, expertisedonated by Microsoft– Jim Gray, Curtis Wong

SkyServer

• Funds from– NSF– STSci (IDEAS grant)– Maryland

Space Grant

• First light: 6/4/2001

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

Contact Information

• Jordan Raddick

(410) 516-8889raddick@pha.jhu.edu

• http://skyserver.sdss.org

The rest of this presentation…

• Is adapted from a SkyServer workshop from an AAPT meeting

• Gives more detail about how to use SkyServer

Retrieving Data with SkyServer

A. Navigation Tool

B. Explore Tool

C. Get Spectra and Get Plates

• 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

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

Radial Search

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

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

• Similar to radial search

• Search area is a rectangular box

continued

Rectangular Search

• Example : Search for objects near Abell 0957

• Select CSV for format

continued

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

How to Learn SQL

• Go to Help -> How-To -> Searching for Data

• Interactive tutorial on SQL

Image List tool

• Go to Tools -> Visual Tools -> Image List

• Click “Use query to fill form”

• Enter query andclick Submit

Image List tool

• Results appear in window

• Click “Send toList”

Image List tool

• Thumbnail for each queryresult

• Click any thumbnail to goto Navigation tool

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

• 4) White dwarfs– Bottom left– Very old,

small, cool

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

Pal 5 from the Palomar Sky Survey

Pal 5 from the 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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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 Diagram of Palomar 5H-R Diagram

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0 0.2 0.4 0.6 0.8 1

g-r

r

H-R Diagrams Side-by-sideH-R Diagram of Palomar 5

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H-R Diagram

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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

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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– raddick@pha.jhu.edu