The Digitized Sky Survey (DSS) is a digitized version of several

photographic Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is employed i ...

astronomical survey An astronomical survey is a general map or image of a region of the sky (or of the whole sky) that lacks a specific observational target. Alternatively, an astronomical survey may comprise a set of images, spectra, or other observations of obje ...

s of the

night sky The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon. Natural light sources in a night sky include ...

, produced by the

Space Telescope Science Institute The Space Telescope Science Institute (STScI) is the science operations center for the Hubble Space Telescope (HST), science operations and mission operations center for the James Webb Space Telescope (JWST), and science operations center for th ...

between 1983 and 2006.

Versions and source material

The term Digitized Sky Survey originally referred to the publication in 1994 of a digital version of an all-sky photographic atlas used to produce the first version of the

Guide Star Catalog The Guide Star Catalog (GSC), also known as the ''Hubble Space Telescope, Guide Catalog'' (''HSTGC''), is a star catalog compiled to support the Hubble Space Telescope with targeting off-axis stars. GSC-I contained approximately 20,000,000 stars w ...

. For the northern sky, the National Geographic Society – Palomar Observatory Sky Survey E-band (red, named after the

Eastman Kodak The Eastman Kodak Company (referred to simply as Kodak ) is an American public company that produces various products related to its historic basis in analogue photography. The company is headquartered in Rochester, New York, and is incorpor ...

IIIa-E

emulsion An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Althoug ...

used), provided almost all of the source data (plate code "XE" in the survey). For the southern sky, the J-band (blue, Eastman Kodak IIIa-J) of the

ESO The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental research organisation made up of 16 member states for ground-based ast ...

/ SERC Southern Sky Atlas (known as the SERC-J, code "S")R. D. Cannon, in ''Astronomy with Schmidt-Type Telescopes'', ed. M. Capaccioli (Springer Netherlands, Astrophysics and Space Science Library), 25 (1984)
/ref> and the "quick" V-band (blue or V in the Johnson–Kron–Cousins system, Eastman Kodak IIa-D) SERC-J Equatorial Extension (SERC-QV, code "XV"), from the

UK Schmidt Telescope The UK Schmidt Telescope (UKST) is a 1.24 metre Schmidt telescope operated by the Australian Astronomical Observatory (formerly the Anglo-Australian Observatory); it is located adjacent to the 3.9 metre Anglo-Australian Telescope at S ...

at the Australian

Siding Spring Observatory Siding Spring Observatory near Coonabarabran, New South Wales, Australia, part of the Research School of Astronomy & Astrophysics (RSAA) at the Australian National University (ANU), incorporates the Anglo-Australian Telescope along with a coll ...

, were used. Three supplemental plates in the V-band from the SERC and Palomar surveys are included (code "XX"), with shorter exposure times for the fields containing the

Andromeda Galaxy The Andromeda Galaxy (IPA: ), also known as Messier 31, M31, or NGC 224 and originally the Andromeda Nebula, is a barred spiral galaxy with the diameter of about approximately from Earth and the nearest large galaxy to the Milky Way. The gala ...

, the

Large Large means of great size. Large may also refer to: Mathematics * Arbitrarily large, a phrase in mathematics * Large cardinal, a property of certain transfinite numbers * Large category, a category with a proper class of objects and morphisms (or ...

and the Small Magellanic Cloud. The publication of a digital version of these photographic collections has subsequently become known as the First Generation DSS or DSS1. After the original 1994 publication, more digitizations were made using recently completed photographic surveys, and released as the Second Generation DSS or DSS2. Second Generation DSS consists of three spectra bands, blue, red, and

near infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from arou ...

. The red part was first to complete, and includes the F-band (red, Eastman Kodak IIIa-F) plates from the

Palomar Observatory Sky Survey II Palomar Observatory is an astronomical research observatory in San Diego County, California, United States, in the Palomar Mountain Range. It is owned and operated by the California Institute of Technology (Caltech). Research time at the observ ...

, made with the Oschin Schmidt Telescope at

Palomar Observatory Palomar Observatory is an astronomical research observatory in San Diego County, California, United States, in the Palomar Mountain Range. It is owned and operated by the California Institute of Technology (Caltech). Research time at the observat ...

for the northern sky. Red band sources for the southern sky include the short red (SR) plates of the SERC I/SR Survey and Atlas of the Milky Way and Magellanic Clouds (referred to as AAO-SR in DSS2), the Equatorial Red (SERC-ER), and the F-band Second Epoch Survey (referred to as AAO-SES in DSS2, AAO-R in the original literature), all made with the UK Schmidt Telescope at Anglo-Australian Observatory.

Production

The Digitized Sky Survey was produced by the Catalogs and Survey Branch (CASB) of the

(STScI). They scanned plates using one of two

Perkin-Elmer PerkinElmer, Inc., previously styled Perkin-Elmer, is an American global corporation focused in the business areas of diagnostics, life science research, food, environmental and industrial testing. Its capabilities include detection, imaging, inf ...

PDS 2020G

microdensitometer A microdensitometer is an optical instrument used to measure optical densities in the microscopic domain. J. C. Dainty and R. Shaw, ''Image Science'' (Academic, New york, 1974).T. H. James, ''The Theory of the Photographic Process'' (Eastman Kodak ...

s. The

pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the smal ...

size was 25 ("First Generation", DSS1) or 15

micrometre The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

s ("Second Generation", DSS2), corresponding to 1.7 or 1.0

arcseconds A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The ...

in the source material. The scanning resulted in images 14,000 x 14,000 (DSS1) or 23,040 x 23,040 pixels (DSS2) in size, or approximately 0.4 (DSS1) and 1.1

gigabyte The gigabyte () is a multiple of the unit byte for digital information. The prefix ''giga'' means 109 in the International System of Units (SI). Therefore, one gigabyte is one billion bytes. The unit symbol for the gigabyte is GB. This defini ...

s (DSS2) each. The scanning of First Generation DSS takes a little under seven hours per plate to complete. Due to the large size of the images, they were compressed using an H-transform algorithm. This algorithm is lossy, but adaptive, and preserves most of the information in the original. Most of the First Generation DSS files were shrunk by a factor of seven. Similar methods were used in the production of the "Second Generation" DSS, but the microdensitometers have since been modified for multi-channel operation, in order to keep the scan time under 12 hours per plate. The CASB has also published several companion scientific products. The most notable is a photometric calibration of part of the "First Generation" DSS. It allows photometric measurements to be made using the digital northern POSS-E, southern SERC-J, and southern Galactic Plane SERC-V data.

Publication

The compressed version of the First Generation DSS was published by the STScI and the Astronomical Society of the Pacific (ASP) on 102 CD-ROMs in 1994, under the name "Digitized Sky Survey." It has also been made available online by the STScI and several other facilities in databases that can be queried over the web. The moniker "First Generation" was added later. In 1996, a more highly compressed version of the DSS was published by the STScI and ASP under the name RealSky. RealSky files were compressed by a factor of roughly 100. RealSky consequently took up less space, but the additional compression made it inappropriate for use in photometry and fine detail in the images was degraded. The Second Generation DSS has appeared steadily over the course of several years. In 2006, the Second Generation DSS (second epoch POSS-II and SES surveys) was finished, and distributed on

CD-ROM A CD-ROM (, compact disc read-only memory) is a type of read-only memory consisting of a pre-pressed optical compact disc that contains data. Computers can read—but not write or erase—CD-ROMs. Some CDs, called enhanced CDs, hold both comput ...

to partner institutions. Generally, the data are available through WWW services at partner institutions.

Funding

References

External links