The Digitized Sky Survey (DSS) is a

digitized Digitization is the process of converting information into a digital (i.e. computer-readable) format.Collins Dictionary. (n.d.). Definition of 'digitize'. Retrieved December 15, 2021, from https://www.collinsdictionary.com/dictionary/english ...

version of several

photographic Photography is the art, application, and practice of creating 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 in many ...

astronomical survey An astronomical survey is a general celestial cartography, map or astrophotography, 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 image ...

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 moonlig ...

, 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 the ...

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 The National Geographic Society – Palomar Observatory Sky Survey (NGS-POSS, or just POSS, also POSS I) was a major astronomical survey, that took almost 2,000 photographic plates of the night sky. It was conducted at Palomar Observatory, Califor ...

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 film photography. The company is headquartered in Rochester, New York, and is incorporated i ...

IIIa-E

emulsion An emulsion is a mixture of two or more liquids that are normally Miscibility, 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 colloi ...

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 Southern Observatory is an astronomical research organisation. ESO may also refer to: *Employee stock option (also: executive stock option) *'' Ether Saga Odyssey'', a fantasy massively multiplayer online role-playing game *''The Elde ...

/ SERC Southern Sky Atlas (known as the SERC-J, code "S") 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 ...

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 is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a Galaxy#Isophotal diameter, D25 isop ...

, 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 (o ...

and the

Small Magellanic Cloud The Small Magellanic Cloud (SMC) is a dwarf galaxy near the Milky Way. Classified as a dwarf irregular galaxy, the SMC has a D25 isophotal diameter of about , and contains several hundred million stars. It has a total mass of approximately 7 bill ...

. 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 that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those o ...

. 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, made with the

Oschin Schmidt Telescope The Samuel Oschin telescope (), also called the Oschin Schmidt, is a Schmidt camera at the Palomar Observatory in northern San Diego County, California, United States. It consists of a Schmidt corrector plate and a (f/2.5) mirror. The instrumen ...

Palomar Observatory The Palomar Observatory is an astronomical research observatory in the Palomar Mountains of San Diego County, California, United States. 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 that was founded in 1937 and originally focused on precision optics. Over the years it went into and out of several different businesses via acquisitions and di ...

PDS 2020G

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

s. The

pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a Raster graphics, raster image, or the smallest addressable element in a dot matrix display device. In most digital display devices, p ...

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

micrometre The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...

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

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

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 SI prefix, prefix ''giga-, giga'' means 109 in the International System of Units (SI). Therefore, one gigabyte is one billion bytes. The unit symbol for the gigabyte i ...

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 The Astronomical Society of the Pacific (ASP) is an American scientific and educational organization, founded in San Francisco on February 7, 1889, immediately following the solar eclipse of January 1, 1889. Its name derives from its origins on ...

(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 computer data storage, data computers can read, but not write or erase. Some CDs, called enhanced CDs, hold b ...

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

Funding

References

External links