Digitized Sky Survey
Encyclopedia
The Digitized Sky Survey (DSS) is a digital
version of several photographic
atlas
es of the night sky
, and an ongoing project to produce more digital versions of photographic astronomical
datasets.
provided almost all of the source data. For the southern sky, the Southern Sky Atlas and its Equatorial Extension (together known as the SERC-J) and the southern Galactic Plane survey (SERC-V), from the UK Schmidt Telescope
at Anglo-Australian Observatory
, were used. The publication of a digital version of these photographic collections has subsequently become known as the First Generation DSS.
After the original 1994 publication, more digitizations were made and released as the Second Generation DSS. They include the Palomar Observatory Sky Survey II, made with the Oschin Schmidt Telescope at Palomar Observatory
for the northern sky. Sources for the southern sky included the 'Galactic Red' survey, the Equatorial Red Survey, and the Second Epoch Survey, all made with the UK Schmidt Telescope at Anglo-Australian Observatory.
(STScI). They scanned plates using one of two Perkin-Elmer PDS 2020G microdensitometers. The pixel
size was 25 or 15 micrometre
s, corresponding to 1.7 or 1.0 arcseconds in the source material. The scanning resulted in images 14,000 x 14,000 or 23,040 x 23,040 pixels in size, or approximately 0.4 and 1.1 gigabyte
s each. The scanning 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 dual-channel operation.
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.
In 1996, a more highly compressed version of the DSS was published by the Astronomical Society of the Pacific
under the name RealSky
.
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 CDROM to partner institutions. Generally, the data are available through WWW services at partner institutions.
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
version of several photographic
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
atlas
Atlas
An atlas is a collection of maps; it is typically a map of Earth or a region of Earth, but there are atlases of the other planets in the Solar System. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats...
es of the night sky
Night sky
The term night sky refers to the sky as seen at night. The term is usually associated with astronomy, with reference to views of celestial bodies such as stars, the Moon, and planets that become visible on a clear night after the Sun has set. Natural light sources in a night sky include moonlight,...
, and an ongoing project to produce more digital versions of photographic astronomical
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
datasets.
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. For the northern sky, the National Geographic Society - Palomar Observatory Sky SurveyNational Geographic Society - Palomar Observatory Sky Survey
The National Geographic Society – Palomar Observatory Sky Survey is a major photographic survey of the night sky that was completed at Palomar Observatory in 1958.-Observations:...
provided almost all of the source data. For the southern sky, the Southern Sky Atlas and its Equatorial Extension (together known as the SERC-J) and the southern Galactic Plane survey (SERC-V), from the UK Schmidt Telescope
UK Schmidt Telescope
The 1.2 metre UK Schmidt Telescope is operated by the Australian Astronomical Observatory , and located adjacent to the 3.9 metre Anglo-Australian Telescope at Siding Spring Observatory, Australia...
at Anglo-Australian Observatory
Anglo-Australian Observatory
The Australian Astronomical Observatory , formerly the Anglo-Australian Observatory, is an optical/near-infrared astronomy observatory with its headquarters in suburban Sydney, Australia...
, were used. The publication of a digital version of these photographic collections has subsequently become known as the First Generation DSS.
After the original 1994 publication, more digitizations were made and released as the Second Generation DSS. They include the Palomar Observatory Sky Survey II, made with the Oschin Schmidt Telescope at Palomar Observatory
Palomar Observatory
Palomar Observatory is a privately owned observatory located in San Diego County, California, southeast of Pasadena's Mount Wilson Observatory, in the Palomar Mountain Range. At approximately elevation, it is owned and operated by the California Institute of Technology...
for the northern sky. Sources for the southern sky included the 'Galactic Red' survey, the Equatorial Red Survey, and the Second Epoch Survey, all made with the UK Schmidt Telescope at Anglo-Australian Observatory.
Production
The "First Generation" Digitized Sky Survey was produced by the Catalogs and Survey Branch (CASB) of the Space Telescope Science InstituteSpace Telescope Science Institute
The Space Telescope Science Institute is the science operations center for the Hubble Space Telescope and for the James Webb Space Telescope...
(STScI). They scanned plates using one of two Perkin-Elmer PDS 2020G microdensitometers. The pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
size was 25 or 15 micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
s, corresponding to 1.7 or 1.0 arcseconds in the source material. The scanning resulted in images 14,000 x 14,000 or 23,040 x 23,040 pixels in size, or approximately 0.4 and 1.1 gigabyte
Gigabyte
The gigabyte is a multiple of the unit byte for digital information storage. The prefix giga means 109 in the International System of Units , therefore 1 gigabyte is...
s each. The scanning 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 dual-channel operation.
The CASB has also published several companion scientific products. The most notable is a photometric
Photometry (astronomy)
Photometry is a technique of astronomy concerned with measuring the flux, or intensity of an astronomical object's electromagnetic radiation...
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 on 102 CD-ROMs in 1994, under the name "Digitized Sky Survey." It has also been published by 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 Astronomical Society of the Pacific
Astronomical Society of the Pacific
The Astronomical Society of the Pacific is a scientific and educational organization, founded in San Francisco on February 7, 1889. Its name derives from its origins on the Pacific Coast, but today it has members all over the country and the world...
under the name RealSky
RealSky
RealSky is the name of a commercially available, digital photographic sky atlas. It is a subset of the Digitized Sky Survey and was published in 1996 by the Astronomical Society of the Pacific....
.
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 CDROM to partner institutions. Generally, the data are available through WWW services at partner institutions.
Funding
- Space Telescope Science InstituteSpace Telescope Science InstituteThe Space Telescope Science Institute is the science operations center for the Hubble Space Telescope and for the James Webb Space Telescope...
- Association of Universities for Research in AstronomyAssociation of Universities for Research in AstronomyThe Association of Universities for Research in Astronomy is a consortium of universities and other institutions that operates astronomical observatories and telescopes...
- Anglo-Australian ObservatoryAnglo-Australian ObservatoryThe Australian Astronomical Observatory , formerly the Anglo-Australian Observatory, is an optical/near-infrared astronomy observatory with its headquarters in suburban Sydney, Australia...
- Beijing Astronomical Observatory
- Canadian Astronomical Data Center
- Centre de Donnee Stellaire
- European Southern ObservatoryEuropean Southern ObservatoryThe European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...
- Gemini ObservatoryGemini ObservatoryThe Gemini Observatory is an astronomical observatory consisting of two telescopes at sites in Hawai‘i and Chile. Together, the twin Gemini telescopes provide almost complete coverage of both the northern and southern skies...
- Hohenkarpfen Observatory
- National Astronomical Observatory of JapanNational Astronomical Observatory of JapanThe is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations - the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude...
- Palomar ObservatoryPalomar ObservatoryPalomar Observatory is a privately owned observatory located in San Diego County, California, southeast of Pasadena's Mount Wilson Observatory, in the Palomar Mountain Range. At approximately elevation, it is owned and operated by the California Institute of Technology...
- Royal Observatory Edinburgh
See also
- RealSkyRealSkyRealSky is the name of a commercially available, digital photographic sky atlas. It is a subset of the Digitized Sky Survey and was published in 1996 by the Astronomical Society of the Pacific....
- National Geographic Society - Palomar Observatory Sky SurveyNational Geographic Society - Palomar Observatory Sky SurveyThe National Geographic Society – Palomar Observatory Sky Survey is a major photographic survey of the night sky that was completed at Palomar Observatory in 1958.-Observations:...
- Southern Sky Survey
- Palomar Observatory Sky Survey II
- Two Micron All-Sky Survey2MASSObservations for the Two Micron All-Sky Survey began in 1997 and were completed in 2001 at two telescopes located one each in the northern and southern hemispheres to ensure coverage of the entire sky...
- Sloan Digital Sky SurveySloan Digital Sky SurveyThe Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project was named after the Alfred P...