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6 Catalogues and Constellations
the Hipparcos catalogue. The Hipparcos catalogue is being superseded by the Gaia
catalogue with an order of magnitude more objects in more bands and to fainter
magnitudes.
Two further catalogues were derived from the Hipparcos observations. Tycho1 contains approximately 1 million entries down to a V magnitude of 11.5, while
Tycho-2, which supersedes Tycho-1, contains 2.5 million objects down to a limiting
magnitude similar to that of Tycho-1. Tycho object numbers are prefixed with TYC
and consist of three numbers separated by a dash. The first number is the Hubble
Guide Star Region; the second is the star number within that region, and the last is
the component identifier for multiple star systems. Hence α Ori is TYC 129-1873-1
in Tycho-2.
The Hubble Guide Star Catalogue
The Hubble Guide Star Catalogue (GSC) was designed as the pointing catalogue
for the Hubble Space Telescope and has been upgraded a number of times, with
the current version at the time of writing being GSC-2, which is intended to be the
pointing catalogue for Hubble’s successor, the James Webb Space Telescope. The
GSC contains over a billion objects, with the majority having J and f magnitudes
down to around magnitude 21. As the GSC was designed for pointing, multiple star
systems are excluded to avoid confusion within the pointing system. The GSC is
a popular catalogue, used in many astronomical packages. A digital version of the
catalogue can be queried or downloaded from the Space Telescope Science Institute
(STScI). The GSC divides the sky into regions and assigns a number to each source
within a region. A third number (either a 1 or a 2) indicates which CD-ROM the
star is located on and is now normally omitted. In the GSC format, α Ori is GSC
00129-01873.
The Sloan Digital Sky Survey
The Sloan Digital Sky Survey (SDSS) is a very large, very deep survey being conducted by the Sloan Foundation 2.5-m optical telescope at the Apache Point Observatory. The Sloan is very fast for a large telescope, being f/5 with 3
◦ field of view.
Sloan is equipped with a massive 120-megapixels CCD and a 640-fibre integrated
Fibre Spectrograph. The SDSS contains over 500 million stars with magnitudes in
u, g, r, i, z (i.e., Sloan filters) down to magnitude 22. The catalogue also includes 1
million spectra of galaxies. SDSS can be queried via the SDSS website http://www.
sdss.org/.
2MASS is the 2 Microns All Sky Survey, an astronomical survey of the whole
sky in the near infrared J , H , and K s (s is for “short”) utilising two 1.3 m telescopes
located in Arizona and Chile. The survey contains 300 million stars or starlike objects
and a further 1,000,000 galaxies or nebula-like structures. Completed in 2003, the
survey contains objects as faint as approximately magnitude 15.
Although 2MASS is an infrared survey, it contains many optically red objects
missed by other surveys, such as red dwarfs that are within the reach of many teaching
instruments. Likewise, the catalogue has a high degree of completeness (i.e., most of
the objects within its sensitivity limits are detected), and hence most non-solar system
objects you are likely to observe will have 2MASS numbers. 2MASS catalogue
6 Catalogues and Constellations
the Hipparcos catalogue. The Hipparcos catalogue is being superseded by the Gaia
catalogue with an order of magnitude more objects in more bands and to fainter
magnitudes.
Two further catalogues were derived from the Hipparcos observations. Tycho1 contains approximately 1 million entries down to a V magnitude of 11.5, while
Tycho-2, which supersedes Tycho-1, contains 2.5 million objects down to a limiting
magnitude similar to that of Tycho-1. Tycho object numbers are prefixed with TYC
and consist of three numbers separated by a dash. The first number is the Hubble
Guide Star Region; the second is the star number within that region, and the last is
the component identifier for multiple star systems. Hence α Ori is TYC 129-1873-1
in Tycho-2.
The Hubble Guide Star Catalogue
The Hubble Guide Star Catalogue (GSC) was designed as the pointing catalogue
for the Hubble Space Telescope and has been upgraded a number of times, with
the current version at the time of writing being GSC-2, which is intended to be the
pointing catalogue for Hubble’s successor, the James Webb Space Telescope. The
GSC contains over a billion objects, with the majority having J and f magnitudes
down to around magnitude 21. As the GSC was designed for pointing, multiple star
systems are excluded to avoid confusion within the pointing system. The GSC is
a popular catalogue, used in many astronomical packages. A digital version of the
catalogue can be queried or downloaded from the Space Telescope Science Institute
(STScI). The GSC divides the sky into regions and assigns a number to each source
within a region. A third number (either a 1 or a 2) indicates which CD-ROM the
star is located on and is now normally omitted. In the GSC format, α Ori is GSC
00129-01873.
The Sloan Digital Sky Survey
The Sloan Digital Sky Survey (SDSS) is a very large, very deep survey being conducted by the Sloan Foundation 2.5-m optical telescope at the Apache Point Observatory. The Sloan is very fast for a large telescope, being f/5 with 3
◦ field of view.
Sloan is equipped with a massive 120-megapixels CCD and a 640-fibre integrated
Fibre Spectrograph. The SDSS contains over 500 million stars with magnitudes in
u, g, r, i, z (i.e., Sloan filters) down to magnitude 22. The catalogue also includes 1
million spectra of galaxies. SDSS can be queried via the SDSS website http://www.
sdss.org/.
2MASS is the 2 Microns All Sky Survey, an astronomical survey of the whole
sky in the near infrared J , H , and K s (s is for “short”) utilising two 1.3 m telescopes
located in Arizona and Chile. The survey contains 300 million stars or starlike objects
and a further 1,000,000 galaxies or nebula-like structures. Completed in 2003, the
survey contains objects as faint as approximately magnitude 15.
Although 2MASS is an infrared survey, it contains many optically red objects
missed by other surveys, such as red dwarfs that are within the reach of many teaching
instruments. Likewise, the catalogue has a high degree of completeness (i.e., most of
the objects within its sensitivity limits are detected), and hence most non-solar system
objects you are likely to observe will have 2MASS numbers. 2MASS catalogue