66
6 Catalogues and Constellations
6.3 Catalogues
Broadly, catalogues can be divided into stellar and nonstellar, although a small number are mixed. Additionally, catalogues can be further split into the historical divisions
of visual, photographic, and digital observing, although a number of photographic
surveys have now been digitised, which is a boon for those who wish to undertake
proper motion studies requiring long gaps between observations.
You should be aware that many catalogues are geographically limited, in that
they are taken with a single ground-based instrument that cannot see the entire sky.
Likewise, not all objects capable of being detected by the survey will be in the
catalogue, as some will always be missed. The number of detected objects compared
to the number of expected detected objects from current computer models is the
completeness. Most modern surveys have completeness levels in excess of 90%, but
you should not be surprised if you find an object that is not in the catalogue you are
using.
As stated above, the bright stars are extremely useful for anyone observing the
night sky, and the ability to identify bright stars will greatly enhance the amount of
observing time you will get at most teaching observatories, especially when things go
wrong, as they often do. Unlike the names of the constellations, the common names
of bright stars come mostly from the Arabic, with some Greek and anglicised names
in use. Most telescopes equipped with GoTo controllers use the common name for
bright stars.
Bayer Catalogue
Most astronomers use Johann Bayer’s 1603 catalogue of approximately 2,500 of
the brightest stars. Bayer used Greek letters and the constellation name, now often
abbreviated, to identify each star in his catalogue, with alpha being the brightest,
beta the second brightest, etc. Hence, α UMa is the brightest star in the constellation
Ursa Major. Of course, there are far more stars in any constellation than there are
Greek letters (in fact, there are approximately 10,000 stars visible with the naked
eye), so this process applies only to the brightest, but it is very useful nonetheless.
While we are on the subject of Bayer’s catalogue, you should be aware that there
are a number of errors in the ordering by brightness. For example, α and β Gem are
the wrong way around. This error and others have never been corrected, and their
existence is a topic of discussion within the astronomy community, as it is not clear
whether such anomalies are truly errors or whether there has been an actual physical
change in one or more of the stars. Whatever the reason, you should attempt to learn
the common and Bayer names of the brightest stars visible from the location from
which you intend to observe. A list some of these stars with their common names is
presented in Table 6.2 along with their visual magnitudes.
Flamsteed Catalogue
Bayer’s catalogue was improved upon with the introduction of a new catalogue by
the first Astronomer Royal, John Flamsteed, in 1712. As with the Bayer catalogue,
the Flamsteed catalogue is geographically limited and did not originally cover the
6 Catalogues and Constellations
6.3 Catalogues
Broadly, catalogues can be divided into stellar and nonstellar, although a small number are mixed. Additionally, catalogues can be further split into the historical divisions
of visual, photographic, and digital observing, although a number of photographic
surveys have now been digitised, which is a boon for those who wish to undertake
proper motion studies requiring long gaps between observations.
You should be aware that many catalogues are geographically limited, in that
they are taken with a single ground-based instrument that cannot see the entire sky.
Likewise, not all objects capable of being detected by the survey will be in the
catalogue, as some will always be missed. The number of detected objects compared
to the number of expected detected objects from current computer models is the
completeness. Most modern surveys have completeness levels in excess of 90%, but
you should not be surprised if you find an object that is not in the catalogue you are
using.
As stated above, the bright stars are extremely useful for anyone observing the
night sky, and the ability to identify bright stars will greatly enhance the amount of
observing time you will get at most teaching observatories, especially when things go
wrong, as they often do. Unlike the names of the constellations, the common names
of bright stars come mostly from the Arabic, with some Greek and anglicised names
in use. Most telescopes equipped with GoTo controllers use the common name for
bright stars.
Bayer Catalogue
Most astronomers use Johann Bayer’s 1603 catalogue of approximately 2,500 of
the brightest stars. Bayer used Greek letters and the constellation name, now often
abbreviated, to identify each star in his catalogue, with alpha being the brightest,
beta the second brightest, etc. Hence, α UMa is the brightest star in the constellation
Ursa Major. Of course, there are far more stars in any constellation than there are
Greek letters (in fact, there are approximately 10,000 stars visible with the naked
eye), so this process applies only to the brightest, but it is very useful nonetheless.
While we are on the subject of Bayer’s catalogue, you should be aware that there
are a number of errors in the ordering by brightness. For example, α and β Gem are
the wrong way around. This error and others have never been corrected, and their
existence is a topic of discussion within the astronomy community, as it is not clear
whether such anomalies are truly errors or whether there has been an actual physical
change in one or more of the stars. Whatever the reason, you should attempt to learn
the common and Bayer names of the brightest stars visible from the location from
which you intend to observe. A list some of these stars with their common names is
presented in Table 6.2 along with their visual magnitudes.
Flamsteed Catalogue
Bayer’s catalogue was improved upon with the introduction of a new catalogue by
the first Astronomer Royal, John Flamsteed, in 1712. As with the Bayer catalogue,
the Flamsteed catalogue is geographically limited and did not originally cover the