Pleiades (star cluster)

The Pleiades (also known as M45 or the Seven Sisters) is an open cluster in the constellation of Taurus. It is among the nearest to earth of all open clusters, probably the best known and certainly the most striking to the naked eye.

Distance

The distance to the Pleiades has been estimated by many methods, as it is an important step in calibrating distance scales for the whole universe. Accurate knowledge of the distance to the Pleiades allows astronomers to plot a Hertzsprung-Russell Diagram for the cluster, which when compared to that plotted for clusters whose distance is not known allows their distance to be estimated. Other methods can then extend the distance scale from open clusters to galaxies and galaxies, and a "distance ladder" can be constructed.

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Results prior to the launch of the Hipparcos satellite generally found that the Pleiades were about 135 parsecs away from Earth. Hipparcos caused consternation among astronomers by finding a distance of only 118 parsecs by measuring the parallax of stars in the cluster—a technique which should yield the most direct and accurate results. Later work has consistently found that the Hipparcos distance measurement for the Pleiades was in error, but it is not known why the error occurred {{ref|Soderblom}}. The distance to the Pleiades is currently thought to be the higher value of about 135 parsecs {{ref|Percival}}, {{ref|Zwahlen}}.

Related Topics:
Hipparcos - Parsec - Earth - Parallax

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