Transcript Talk - The Department of Astronomy and Astrophysics

Using Data from the Sloan
Digital Sky Survey
In the Classroom
Jordan Raddick (Johns Hopkins University)
Visualization of Astrophysical Data workshop
Kavli 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 3D
map 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 to
SDSS data
• Servers donated by
Hewlett-Packard
• Software, expertise
donated 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 professionalquality 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
Change
RA/Dec
Close
up
Display
Options
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 specific
magnitudes
• 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) 516-8889
[email protected]
• 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
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
Navigation Tool
Object Explorer
• Information on
single objects
– Photometric and
spectroscopic
• Look up by
object ID, position,
• Correlations to
data from other sky
surveys
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.
B.
C.
D.
E.
Radial Search
Rectangular Search
SQL Search
Schema Browser
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 limit
continued
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 file
Use Excel’s “Text Import
Wizard”
• Open Excel
• From the Data
menu,select Get
External Data ->
Import Text File
Rectangular Search
• Select “Delimited,”
then “Comma”
• Change any
objid columns to
“Text”
• This preserves
all 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 and
click Submit
Image List tool
• Results appear
in window
• Click “Send to
List”
Image List tool
• Thumbnail for
each query
result
• Click any
thumbnail to go
to 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 brightnesses shows up
• Magnitude is
logarithmic, so
take difference in
magnitudes
– 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 massive stars on
left top
The H-R Diagram
• 2) Red giants
– Middle right
– Older stars
• 3) Supergiants
– “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 Diagram
H-R Diagram of Palomar 5
g-r
0
0.2
0.4
0.6
14
15
16
r
17
18
19
20
21
22
23
24
Yours will probably look different!
0.8
1
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 5
H-R Diagram
g-r
r
0
14
15
16
17
18
19
20
21
22
23
24
0.2
0.4
0.6
0.8
1
H-R Diagrams Side-by-side
H-R Diagram of Palomar 5
g-r
0
0.2
0.4
0.6
0.8
1
14
15
16
From images
19
20
21
22
23
24
H-R Diagram
g-r
0
From query
r
r
17
18
14
15
16
17
18
19
20
21
22
23
24
0.2
0.4
0.6
0.8
1
Interpreting the H-R Diagram
• See the:
H-R Diagram
0.2
0.4
0.6
0.8
r
– Main
0
14
sequence
15
16
17
– Red giants
18
19
20
– Horizontal
21
22
branch
23
(supergiants) 24
– White dwarfs too faint
g-r
• Where are big main sequence stars???
1
Interpreting the H-R Diagram
• They burned
out their fuel
and became
red giants!
• “Turnoff” from
main seq
tells you age
of cluster
• So how old is Palomar 5?
r
0
14
15
16
17
18
19
20
21
22
23
24
0.2
H-R Diagram
g-r
0.4
0.6
0.8
1
Interpreting the H-R Diagram
• Hard to tell
• Where is
turnoff?
• Somewhere
between
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 Standards
continued
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]