InSAR
Interferometric
Synthetic Aperture
Radar

GIOD
Globally Interconnected Object Databases

LIGO
Laser Interferometer Gravitational-Wave Observatory)

XSIL
Extensible Scientific Interchange Language

What is the Digital Sky?

Depicted in this illustration is the constellation “Canes Venatici” from the Firmamentum Sobiescianem sive Uranographia, by Johannes Hevelius of Gdansk, 1690 — in fact, Hevelius was the first to introduce this constellation. Behind the right ear of the dog Chara is a cluster of galaxies known as SA-57, from which the images in the next figure are taken.
Image courtesy of the Linda Hall Library, Kansas City, Missouri

(Click for full figure)

Each galaxy is shown in the three infrared bands of the 2MASS survey, and also in visible light from the Palomar Sky Survey. The colored ellipses represent how the images are processed and thereby converted to catalogs of objects with numerical attributes. In this case, the dark blue elliptical contour represents the 20 magnitude per square arcsecond isophotal area, and the cyan contour the “flux growth” elliptical area. Sources that had been “subtracted” from the object fields are circled in red, and sources circled in green represent sources that were previously processed and subsequently blanked from the object field. Once images are converted to a catalog in this way, new kinds of tools are available to the astronomer; tools that use databases and statistics to derive new knowledge of the cosmos.
More Information

Among the surveys being undertaken are the Digital Palomar Observatory Sky Survey (DPOSS), the 2-Micron All Sky Survey (2MASS), the NRAO VLA Sky Survey (NVSS), and the VLA FIRST radio survey. We are also coordinating with another major survey, the Sloan Digital Sky Survey, and will be working towards adopting standards and conventions that will allow common access of all the surveys in the future. The Digital Sky project will provide simultaneous access to the catalogs and image data, together with sufficient computing capability to allow detailed correlated studies across the entire dataset. Not all the data will be literally online. While the metadata is expected to be, the actual databases are so voluminous that they will reside in the HPSS (High Performance Storage System) archival storage systems at the Center for Advanced Computing Research (CACR) at Caltech, and at San Diego Supercomputer Center (SDSC). However, a database system will be interfaced to HPSS to enable users of the Digital Sky to issue database queries even for data in the HPSS archive.

The data from the Palomar, 2MASS, and NVSS surveys are expected to yield over one billion sources, and the image data will comprise several tens of terabytes. Astronomers will be able to launch sophisticated queries to the catalogs describing the optical, radio, and infrared sources, and then undertake detailed analysis of the images for morphological and statistical studies of both discrete sources and extended structures. Our computing facilities, both in CACR and at San Diego, will provide significant capability for pattern recognition, automatic searching and cataloging, and computer assisted data analysis.

Significant results have already been obtained from the surveys. For instance, initial explorations of the digital Palomar database (DPOSS) have yielded discoveries of a number of high-redshift quasars. Having the full dataset online together with radio and IR surveys would increase the scientific potential of these data by orders of magnitude. Indeed, the full science potential of the surveys will only be realized with the multi-terabyte/teraflops capabilities provided by the NPACI facilities.

While initially we will work on the four primary surveys, we also plan to soon incorporate other catalogs and surveys such as the ROSAT and IRAS all-sky surveys in the X-ray and longer-wavelength IR regions of the spectrum, and the Westerbork 327-MHz survey (WENSS). As other surveys come on-line they will be able to take immediate advantage of the architecture and software developed in the Digital Sky and Sloan projects.