Virtual Sky project provides not only stunning images of the night
sky, but also a seamless composite view of the northern heavens.
Anyone can use the new Virtual Sky website, which features an easy-to-use,
intuitive interface to high-resolution images from the complete
Digital Palomar Observatory Sky Survey, all of the released data
from the Sloan Digital Sky Survey, and many other surveys taken
in infrared, visible, and radio wavelengths. The Web-based educational
resource is free to the public, teachers, and students who want
to learn about the universe and explore it.
This is part of
NPACIs Digital Sky project, originally available to just professional
astronomers, said the leader of the Virtual Sky project, Roy
Williams of Caltechs Center for Advanced Computing Research.
We realized that we also had the opportunity to use astronomical
databases and supercomputers to provide a resource the general public
Virtual Sky is a collaboration with Microsoft Research, and uses
the same SQL Server database technology as its Terraserver interface
to Earth imagery. Starting with the entire northern sky in the Web
browser window (Figure 1), users can zoom in on any section, magnifying
the view (Figure 2) by up to 2,000 times to an image scale of 1.5
arcseconds per pixelthe best resolution of ground-based photographs.
Zoom, Zoom, Zoom
Virtual Sky is an incredible public asset, said Jim
Gray, manager of Microsoft Researchs Bay Area Research Center
and senior researcher in Microsofts Research Scalable Servers
Research Group. The images and other data were available through
Caltech, but you had to be a professional astronomer to use them
and you had to know what you wanted. Roy single-handedly changed
that, and the results are really stunning.
Microsoft contributed software, Caltech provides most of the operating
expenses, and an anonymous donor contributed hardware to Virtual
Sky worth about $20,000.
The Virtual Sky presents
its information in multiple themes, each one a representation
of the heavens from a different database (Figure 3). Star charts,
provided by YourSky, a Web-based interactive sky atlas, show the
positions and names of stars, constellations, galaxies, and nebulas
on a map grid. But this is just a convenient starting point.
The largest theme is the Digital Palomar Observatory Sky Survey.
Photographic plates taken in blue and red light from a 48-inch
telescope at the Palomar Observatory have been converted to 3
terabytes of digital-image data, encompassing an estimated 50
million galaxies and 3 billion stars. Another theme is the portion
of the sky that has been imaged by the ongoing Sloan Digital Sky
Survey that has been released to the public (about 0.3 terabyte).
Other themes are the Hubble Deep Field, National Optical Astronomy
Observatorys Deep Wide-Field Survey, a radio sky map from
the National Radio Astronomy Observatorys Very Large Array
Sky Survey, x-ray data from the ROSAT satellite, and infrared
images processed from the Infrared Astronomical Satellite. The
project currently has a NASA grant to mosaic infrared imagery
from the Two Micron All Sky Survey.
One of the most engaging themes is the Uranometria, a set of engravings
by German astronomer Johann Bayer (1572-1625), which contains
51 star charts and was the forerunner of all later star atlases.
The book contains both accurate star charts and fanciful drawings
of the mythological figures, which the constellations are supposed
to represent, and is the direct ancestor of the modern system
of star and constellation nomenclature.
All the themes are resampled to the same standard projection,
so a user of the Virtual Sky service can see a region of the sky
in any its different representations, all perfectly aligned and
at the same scale. The database architecture employs a hierarchy
of precomputed image tiles, giving quick response.
Virtual Sky is an unparalleled
educational resource. The natural fascination that we all
have with the night sky can be harnessed to teach not only astronomy,
but also general science and mathematics, said Williams.
On one level, children and adults can simply cruise the
glory of the heavens with the worlds finest telescopes.
Those interested in the history of science might compare the Uranometria
representation with the photographic survey. Historical perspectives
could provide a far-reaching cultural view, considering the questions
of why the star atlases were created, and how mythological stories
have been represented from classical times through the Enlightenment.
More advanced students can compare views of the same regions at
different wavelengths and scales to learn about the properties
of astronomical objects. Students can classify the galaxies they
find on the basis of appearance, and compare their results with
the catalogued Hubble classification. Counts of stars and galaxies
at different scales can be used to teach statistical analysis
techniques. Both amateur and professional astronomers can use
Virtual Sky to prepare finder charts, and they can compare their
observations to Virtual Sky views to aid in the discovery of variable
stars, supernovas, asteroids, and comets.
A novel feature of the Visible Sky service is the weblog (or blog
in insider parlance), a bulletin board where people can record
comments and direct other users to interesting sights. I
think this is incredible, wrote a visitor recently. I
have never seen anything like this. I will e-mail this link to
my friends and let them have a look.
Pick a Theme
The Virtual Sky currently
has 15 million tiles in a 120-gigabyte Microsoft SQL Server database.
Data ingestion for Virtual Sky is a formidable task, with the
Palomar and Sloan data sets requiring weeks of computing and data
transfer. Virtual Sky is complementary to the SDSC and Caltech
focus on data management and data-intensive computing for the
TeraGrid. In addition to big computing, the astronomy
project involves handling multi-terabyte data sets. The data are
on both Microsoft and Unix machines, and much of the processing
involves long, high-bandwidth data flow. Caltech has performed
the high-performance data computing for Virtual Sky, making extensive
use of the HPSS and HP Superdome systems.
The Virtual Sky is connected to other astronomical data services,
such as the NASA/IPAC Extragalactic Databaseclicking on
a galaxy calls up its name, catalog data, and publication references.
Virtual Sky also is being developed as an index into the raw survey
data. Accessing the Sloan, Palomar, and other survey data
that covers a given astronomical object is currently a tedious
task that is idiosyncratic for each survey, Williams said.
We would like Virtual Sky to provide a unified portal, so
from any part of the sky we could automatically retrieve the raw
Much of the analytical
research in astronomy involves access to catalogs of interesting,
similar, or peculiar objects. Modern catalogs are created by pattern-matching
software working on digitized survey images and may contain billions
of objects. Williams sees the Virtual Sky as a way to create catalogs
from federations of image surveys rather than single surveysfor
example, by finding objects that are simultaneously bright in
infrared but faint in the optical.
The NSF-funded National Virtual Observatory, the PACI TeraGrid,
IBM, Microsoft, NASA, and other development teams are creating
open architectures based on XML and associated protocols for Web
services, description, and directory services, Williams
said. We would like to use Virtual Sky as a demonstrator
for this way of doing things, providing not only the services
themselves, but also the subsidiary data that allows interoperation
between data services and astronomy portals.