Mining the Sky
The World-Wide Telescope
Jim Gray
Microsoft Research
Collaborating with:
Alex Szalay, Peter Kunszt, Ani Thakar @ JHU
Robert Brunner, Roy Williams @ Caltech
George Djorgovski, Julian Bunn @ Caltech1
Outline
• The revolution in Computational Science
• The Virtual Observatory Concept
== World-Wide Telescope
• The Sloan Digital Sky Survey
& DB technology
2
Computational Science
The Third Science Branch is Evolving
• In the beginning science was empirical.
• Then theoretical branches evolved.
• Now, we have computational branches.
– Has primarily been simulation
– Growth area data analysis/visualization
of peta-scale instrument data.
• Analysis & Visualization tools
– Help both simulation and instruments.
– Are primitive today.
3
Computational Science
• Traditional Empirical Science
– Scientist gathers data by direct
observation
– Scientist analyzes data
• Computational Science
– Data captured by instruments
Or data generated by simulator
– Processed by software
– Placed in a database / files
– Scientist analyzes database / files
4
Exploring Parameter Space
Manual or Automatic Data Mining
• There is LOTS of data
– people cannot examine most of it.
– Need computers to do analysis.
• Manual or Automatic Exploration
– Manual: person suggests hypothesis,
computer checks hypothesis
– Automatic: Computer suggests hypothesis
person evaluates significance
• Given an arbitrary parameter space:
–
–
–
–
–
–
Data Clusters
Points between Data Clusters
Isolated Data Clusters
Isolated Data Groups
Holes in Data Clusters
Isolated Points
Nichol et al. 2001
Slide courtesy of and adapted from5
Robert Brunner @ CalTech.
Challenge to Data Miners:
Rediscover Astronomy
• Astronomy needs deep
understanding of physics.
• But, some was discovered
as variable correlation
then “explained” with physics.
• Famous example:
Hertzsprung-Russell Diagram
star luminosity vs color (=temperature)
• Challenge 1 (the student test):
How much of astronomy can data mining discover?
• Challenge 2 (the Turing test):
Can data mining discover NEW correlations?
6
What’s needed?
(not drawn to scale)
Miners
Scientists
Science Data
& Questions
Data Mining
Algorithms
Plumbers
Database
To store data
Execute
Queries
Question &
Answer
Visualization
Tools
7
Data Mining:
Science
vs Commerce
• Data in files
•
FTP a local copy /subset.
ASCII or Binary.
• Each scientist builds own •
analysis toolkit
• Analysis is tcl script of •
toolkit on local data.
• Some simple visualization •
tools: x vs y
Data in a database
Standard reports for
standard things.
Report writers for
non-standard things
GUI tools to explore data.
– Decision trees
– Clustering
– Anomaly finders
8
But…some science is hitting a wall
FTP and GREP are not adequate
•
•
•
•
You can GREP 1 MB in a second
You can GREP 1 GB in a minute
You can GREP 1 TB in 2 days
You can GREP 1 PB in 3 years.
•
•
•
•
You can FTP 1 MB in 1 sec
You can FTP 1 GB / min (= 1 $/GB)
…
2 days and 1K$
…
3 years and 1M$
• Oh!, and 1PB ~10,000 disks
• At some point you need
indices to limit search
parallel data search and analysis
• This is where databases can help
9
Why is Science Behind?
• Inertia:
– Science started earlier (Fortran,…)
– Science culture works (no big incentive to change)
• Energy
– Commerce is about profit:
better answers translate to better profits
– So companies to build tools.
• Impedance Mismatch
– Databases don’t accommodate analysis packages
– Scientist’s analysis needs to be inside the dbms.
10
Goal: Easy Data Publication & Access
• Augment FTP with data query:
Return intelligent data subsets
• Make it easy to
– Publish: Record structured data
– Find:
• Find data anywhere in the network
• Get the subset you need
– Explore datasets interactively
• Realistic goal:
– Make it as easy as
publishing/reading web sites today.
11
Web Services: The Key?
• Web SERVER:
– Given a url + parameters
– Returns a web page (often dynamic)
Your
program
Web
Server
• Web SERVICE:
– Given a XML document (soap msg)
– Returns an XML document
– Tools make this look like an RPC.
• F(x,y,z) returns (u, v, w)
– Distributed objects for the web.
– + naming, discovery, security,..
• Internet-scale
distributed computing
Your
program
Data
In your
address
space
Web
Service
12
Data Federations of Web Services
• Massive datasets live near their owners:
–
–
–
–
Near the instrument’s software pipeline
Near the applications
Near data knowledge and curation
Super Computer centers become Super Data Centers
• Each Archive publishes a web service
– Schema: documents the data
– Methods on objects (queries)
• Scientists get “personalized” extracts
• Uniform access to multiple Archives Federation
– A common global schema
13
Grid and Web Services Synergy
• I believe the Grid will have many web services
• IETF standards Provide
– Naming
– Authorization / Security / Privacy
– Distributed Objects
Discovery, Definition, Invocation, Object Model
– Higher level services: workflow, transactions, DB,..
• Synergy: commercial Internet & Grid tools
14
Outline
• The revolution in Computational Science
• The Virtual Observatory Concept
== World-Wide Telescope
• The Sloan Digital Sky Survey
& DB technology
15
Why Astronomy Data?
IRAS 25m
•It has no commercial value
–No privacy concerns
–Can freely share results with others
–Great for experimenting with algorithms
2MASS 2m
•It is real and well documented
–High-dimensional data (with confidence intervals)
–Spatial data
–Temporal data
•Many different instruments from
many different places and
many different times
•Federation is a goal
•The questions are interesting
IRAS 100m
WENSS 92cm
NVSS 20cm
–How did the universe form?
•There is a lot of it (petabytes)
DSS Optical
16
ROSAT ~keV
GB 6cm
Time and Spectral Dimensions
The Multiwavelength Crab Nebulae
Crab star
1053 AD
X-ray,
optical,
infrared, and
radio
views of the nearby
Crab Nebula, which is
now in a state of
chaotic expansion after
a supernova explosion
first sighted in 1054
A.D. by Chinese
Astronomers.
17
Slide courtesy of Robert Brunner @ CalTech.
Even in “optical” images are very different
Optical Near-Infrared Galaxy Image Mosaics
BJ
RF
IN
J
H
K
BJ
RF
IN
J
H
K
One object in
6 different
“color” bands
18
Slide courtesy of Robert Brunner @ CalTech.
Astronomy Data Growth
•
•
•
•
•
In the “old days” astronomers took photos.
Starting in the 1960’s they began to digitize.
New instruments are digital (100s of GB/nite)
Detectors are following Moore’s law.
Data avalanche: double every 2 years
1000
100
Courtesy
of
Alex
Szalay
10
1
0.1
1970
1975
1980
1985
1990
1995
2000
CCDs
Glass
Total area of 3m+
telescopes in the world in
m2, total number of CCD
pixels in megapixel, as a
function of time. Growth
over 25 years is a factor
of 30 in glass, 300019 in
pixels.
Universal Access to Astronomy Data
• Astronomers have a few Petabytes now.
– 1 pixel (byte) / sq arc second ~ 4TB
– Multi-spectral, temporal, … → 1PB
• They mine it looking for
new (kinds of) objects or
more of interesting ones (quasars),
density variations in 400-D space
correlations in 400-D space
•
•
•
•
•
Data doubles every 2 years.
Data is public after 2 years.
So, 50% of the data is public.
Some have private access to 5% more data.
So: 50% vs 55% access for everyone
20
The Age of Mega-Surveys
• Large number of new surveys
– multi-TB in size, 100 million objects or more
– Data publication an integral part of the survey
– Software bill a major cost in the survey
• The next generation mega-surveys are different
–
–
–
–
top-down design
large sky coverage
sound statistical plans
well controlled/documented data processing
• Each survey has a publication plan
MACHO
2MASS
DENIS
SDSS
PRIME
DPOSS
GSC-II
COBE
MAP
NVSS
FIRST
GALEX
ROSAT
OGLE ...
• Federating these archives
Slide courtesy of Alex21Szalay,
 Virtual Observatory
modified by Jim
Data Publishing and Access
• But…..
• How do I get at that 50% of the data?
• Astronomers have culture of publishing.
– FITS files and many tools.
http://fits.gsfc.nasa.gov/fits_home.html
– Encouraged by NASA.
– FTP what you need.
• But, data “details” are hard to document. Astronomers
want to do it but it is VERY hard.
(What programs where used? What were the processing steps? How were errors treated?…)
• And by the way, few astronomers
have a spare petabyte of storage in their pocket.
• THESIS:
Challenging problems are
publishing data
providing good query & visualization tools
22
Virtual Observatory
http://www.astro.caltech.edu/nvoconf/
http://www.voforum.org/
• Premise: Most data is (or could be online)
• So, the Internet is the world’s best telescope:
–
–
–
–
It has data on every part of the sky
In every measured spectral band: optical, x-ray, radio..
As deep as the best instruments (2 years ago).
It is up when you are up.
The “seeing” is always great
(no working at night, no clouds no moons no..).
– It’s a smart telescope:
links objects and data to literature on them.
23
Demo of VirtualSky
• Roy Williams @ Caltech
Palomar Data with links to NED.
• Shows multiple themes,
shows link to other sites (NED, VizeR, Sinbad, …)
•
http://virtualsky.org/servlet/Page?T=3&S=21&P=1&X=0&Y=0&W=4&F=1
And
NED @ http://nedwww.ipac.caltech.edu/index.html
24
Demo of Sky Server
Alex Szalay of Johns Hopkins built SkyServer (based on TerraServer design).
http://skyserver.sdss.org/
25
Virtual Observatory Challenges
• Size : multi-Petabyte
40,000 square degrees is 2 Trillion pixels
– One band (at 1 sq arcsec)
4 Terabytes
– Multi-wavelength
10-100 Terabytes
– Time dimension
>> 10 Petabytes
– Need auto parallelism tools
• Unsolved MetaData problem
– Hard to publish data & programs
– How to federate Archives
– Hard to find/understand data & programs
• Current tools inadequate
– new analysis & visualization tools
– Data Federation is problematic
• Transition to the new astronomy
– Sociological issues
26
Steps to Virtual Observatory Prototype
• Get SDSS and Palomar data online
– Alex Szalay, Jan Vandenberg, Ani Thacker….
– Roy Williams, Robert Brunner, Julian Bunn,…
• Do local queries and crossID matches to expose
– Schema, Units,…
– Dataset problems
– Typical use scenarios.
• Define a set of Astronomy Objects and methods.
– Based on UDDI, WSDL, SOAP.
– Started this with TerraService http://TerraService.net/ ideas.
– Working with Caltech (Brunner, Williams, Djorgovski, Bunn)
and JHU (Szalay et al) on this
– Each archive is a web service
• Move crossID app to web-service base
27
Virtual Observatory and
Education
• The Virtual Observatory can be used to
– Teach astronomy:
make it interactive,
demonstrate ideas and phenomena
– Teach computational science skills
28
Outline
• The revolution in Computational Science
• The Virtual Observatory Concept
== World-Wide Telescope
• The Sloan Digital Sky Survey
& DB technology
29
Sloan Digital Sky Survey
http://www.sdss.org/
• For the last 12 years a group of astronomers
has been building a telescope (with funding
from Sloan Foundation, NSF, and a dozen
universities). 90M$.
• Y2000: engineer, calibrate, commission: now public data.
– 5% of the survey, 600 sq degrees, 15 M objects 60GB, ½ TB raw.
– This data includes most of the known high z quasars.
– It has a lot of science left in it but….
• New the data is arriving:
– 250GB/nite (20 nights per year) = 5TB/y.
– 100 M stars, 100 M galaxies, 1 M spectra.
• http://www.sdss.org/ and http://www.sdss.jhu.edu/
30
Two kinds of SDSS data in an SQL DB
(objects and images all in DB)
• 15M Photo Objects ~ 400 attributes
50K
Spectra
with
~30 lines/
spectrum
31
Spatial Data Access – SQL extension
(Szalay, Kunszt, Brunner) http://www.sdss.jhu.edu/htm
• Added Hierarchical Triangular Mesh (HTM)
table-valued function for spatial joins.
• Every object has a 20-deep Mesh ID.
2
2,3,0
2,0
2,3,1
2,3,2
2,1
2,3,3
2,2
2,3
• Given a spatial definition:
Routine returns up to ~10 covering triangles.
• Spatial query is then up to ~10 range queries.
• Very fast: 10,000 triangles / second / cpu.32
Data Loading
• JavaScript of DB loader (DTS)
• Web ops interface & workflow system
• Data ingest and scrubbing is major effort
– Test data quality
– Chase down bugs / inconsistencies
• Other major task is data documentation
– Explain the data
– Explain the schema and functions.
• If we supported users, …
33
Scenario Design
• Astronomers proposed 20 questions
• Typical of things they want to do
• Each would require a week of programming
in tcl / C++/ FTP
• Goal, make it easy to answer questions
• DB and tools design motivated by this goal
– Implementd utility prodecures
– JHU Built GUI for Linux clients
34
The 20 Queries
Q1: Find all galaxies without unsaturated pixels within 1' of a given
point of ra=75.327, dec=21.023
Q2: Find all galaxies with blue surface brightness between and 23
and 25 mag per square arcseconds, and -10<super galactic
latitude (sgb) <10, and declination less than zero.
Q3: Find all galaxies brighter than magnitude 22, where the local
extinction is >0.75.
Q4: Find galaxies with an isophotal surface brightness (SB) larger
than 24 in the red band, with an ellipticity>0.5, and with the
major axis of the ellipse having a declination of between 30”
and 60”arc seconds.
Q5: Find all galaxies with a deVaucouleours profile (r¼ falloff of
intensity on disk) and the photometric colors consistent with
an elliptical galaxy. The deVaucouleours profile
Q6: Find galaxies that are blended with a star, output the deblended
galaxy magnitudes.
Q7: Provide a list of star-like objects that are 1% rare.
Q8: Find all objects with unclassified spectra.
Q9: Find quasars with a line width >2000 km/s and
2.5<redshift<2.7.
Q10: Find galaxies with spectra that have an equivalent width in Ha
>40Å (Ha is the main hydrogen spectral line.)
Q11: Find all elliptical galaxies with spectra that have an
anomalous emission line.
Q12: Create a grided count of galaxies with u-g>1 and r<21.5 over
60<declination<70, and 200<right ascension<210, on a grid
of 2’, and create a map of masks over the same grid.
Q13: Create a count of galaxies for each of the HTM triangles
which satisfy a certain color cut, like 0.7u-0.5g-0.2i<1.25 &&
r<21.75, output it in a form adequate for visualization.
Q14: Find stars with multiple measurements and have magnitude
variations >0.1. Scan for stars that have a secondary object
(observed at a different time) and compare their magnitudes.
Q15: Provide a list of moving objects consistent with an asteroid.
Q16: Find all objects similar to the colors of a quasar at
5.5<redshift<6.5.
Q17: Find binary stars where at least one of them has the colors of
a white dwarf.
Q18: Find all objects within 30 arcseconds of one another that have
very similar colors: that is where the color ratios u-g, g-r, r-I
are less than 0.05m.
Q19: Find quasars with a broad absorption line in their spectra and
at least one galaxy within 10 arcseconds. Return both the
quasars and the galaxies.
Q20: For each galaxy in the BCG data set (brightest color galaxy),
in 160<right ascension<170, -25<declination<35 count of
galaxies within 30"of it that have a photoz within 0.05 of that
galaxy.
Also some good queries at:
http://www.sdss.jhu.edu/ScienceArchive/sxqt/sxQT/Example_Queries.html
35
An Easy One
Q15: Provide a list of moving objects consistent with an
asteroid.
• Sounds hard but
there are 5 pictures of the object at 5 different times
(color filters) and so can “see” velocity.
• Image pipeline computes velocity.
• Computing it from the 5 color x,y would also be fast
• Finds 1,303 objects in 3 minutes, 140MBps.
(could go 2x faster with more disks)
select objId, dbo.fGetUrlEq(ra,dec) as url
--return object ID & url
sqrt(power(rowv,2)+power(colv,2)) as velocity
from
photoObj
-- check each object.
where (power(rowv,2) + power(colv, 2))
-- square of velocity
between 50 and 1000
-- huge values =error
37
Q15: Fast Moving Objects
• Find near earth asteroids:
SELECT r.objID as rId, g.objId as gId,
dbo.fGetUrlEq(g.ra, g.dec) as url
FROM PhotoObj r, PhotoObj g
WHERE r.run = g.run and r.camcol=g.camcol
and abs(g.field-r.field)<2 -- nearby
-- the red selection criteria
and ((power(r.q_r,2) + power(r.u_r,2)) > 0.111111 )
and r.fiberMag_r between 6 and 22 and r.fiberMag_r < r.fiberMag_g
and r.fiberMag_r < r.fiberMag_i
and r.parentID=0 and r.fiberMag_r < r.fiberMag_u
and r.fiberMag_r < r.fiberMag_z
and r.isoA_r/r.isoB_r > 1.5 and r.isoA_r>2.0
-- the green selection criteria
and ((power(g.q_g,2) + power(g.u_g,2)) > 0.111111 )
and g.fiberMag_g between 6 and 22 and g.fiberMag_g < g.fiberMag_r
and g.fiberMag_g < g.fiberMag_i
and g.fiberMag_g < g.fiberMag_u and g.fiberMag_g < g.fiberMag_z
and g.parentID=0 and g.isoA_g/g.isoB_g > 1.5 and g.isoA_g > 2.0
-- the matchup of the pair
and sqrt(power(r.cx -g.cx,2)+ power(r.cy-g.cy,2)+power(r.cz-g.cz,2))*(10800/PI())< 4.0
and abs(r.fiberMag_r-g.fiberMag_g)< 2.0
• Finds 3 objects in 11 minutes
– (or 52 seconds with an index)
• Ugly,
38
but consider the alternatives (c programs an files and…)
–
39
40
41
Performance (on current SDSS data)
IO count
• Run times: on 15k$ COMPAQ Server
(2 cpu, 1 GB , 8 disk)
cpu vs IO
1E+7
• Some take 10 minutes
1E+6
1E+5
• Some take 1 minute
100 IOs/cpu sec
1E+4
1E+3
• Median ~ 22 sec.
1E+2
• Ghz processors are fast! 1E+1
– (10 mips/IO, 200 ins/byte)
– 2.5 m rec/s/cpu
seconds
1000
1E+0
0.01
1.
10.
100.
1,000.
CPU sec
10
1
0.1
time vs queryID
cpu
elapsed
100
~1000 IO/cpu sec
~ 70 MB IO/cpu sec
ae
Q08
Q01
Q09
Q10A
Q19
Q12
Q10
Q20
Q16
Q02
Q13
Q04
Q06
Q11
Q15B
Q17
Q07
Q14
Q15A
Q05
Q03
42
Q18
Summary of Queries
• All have fairly short SQL programs -a substantial advance over (tcl, C++)
• Many are sequential
one-pass and two-pass over data
• Covering indices make scans run fast
• Table valued functions are wonderful
but limitations are painful.
• Counting, Binning, Histograms VERY common
• Spatial indices helpful,
• Materialized view (Neighbors) helpful.
43
Call to Action
• If you do data visualization: we need you
(and we know it).
• If you do databases:
here is some data you can practice on.
• If you do distributed systems:
here is a federation you can practice on.
• If you do data mining
here are datasets to test your algorithms.
• If you do astronomy educational outreach
here is a tool for you.
• The astronomers are very good, and very smart, and a
pleasure to work with, and
44
the questions are cosmic, so …
45
SDSS what I have been doing
• Work with Alex Szalay, Don Slutz, and others to
define 20 canonical queries and
10 visualization tasks.
• Working with Alex Szalay on
building Sky Server and
making data it public
(send out 80GB SQL DBs)
54