The Hyades, Melotte 25

Right Ascension	4 : 27 (h:m)
Declination	+16 : (deg:m)
Distance	0.150 (kly)
Visual Brightness	0.5 (mag)
Apparent Dimension	330 (arc min)

Known pre-historically.

At a distance of only about 150 light years, the Hyades form the nearest open cluster to us, disregarding the Ursa Major cluster which appears as spread individual stars. Their distance is quite wellknown from their motion along a common direction: All member stars move toward a point slightly east of Betelgeuse (alpha in Orion), about at RA=6:08, Dec=+9.1 degrees. From their radial velocity, which is about 43 km/sec in recession, and from their proper motion the distance is not difficult to be derived. The distance has also been well confirmed by data obtained by ESA's astrometric satellite Hipparcos, which found a distance of 151 light years.

The central group is roughly 10 light years in diameter, while outlying members seem to be spread over a volume of at least 80 light years diameter. The cluster's Hertzsprung-Russell diagram corresponds to the HRD of a theoretical cluster of 790 million years age, therefore it is concluded that this cluster is 790 million years old. This age, as well as the stellar contents of this cluster, and its proper spatial motion suggests that probably the Hyades have a common origin with the Praesepe star cluster M44, which is estimated from its HRD at 730 million years (older estimates had given, for both clusters in each case, an age of 400 and 660 million years).

The Hyades are known prehistorically. Like the Pleiades (M45), they were mentioned by Homer about 750 B.C. and by Hesiod about 700 B.C, and later by a number of other ancient authors, including Pherecydes, Hyginus, Pliny, Vergil, Horace and Ovid. They were perhaps first cataloged by Hodierna in his 1654 publication and later by Melotte in 1915 (as Mel 25). They were commonly included in 17th and 18th century star atlasses and charts, e.g. those used by Charles Messier, and described by Johann Elert Bode in 1782.

The common motion of the Hyades and a number of more stars (the Taurus or Hyades stream) and thus their physical connection was first demonstrated by Lewis Boss in 1908, according to Burnham.

The brightest star in the field of the Hyades, bright red giant star Aldebaran (Alpha Tauri), visible on the right hand side of our image, is not a member of the cluster and situated much closer to us (about 60 light years, a factor 2.5 closer than the Hyades).

The image in our page was obtained by Till Credner and Sven Kohle; it is an extract from their Constellation Taurus photography. The original image covers an area of 35 x 24 degrees in the sky, and was obtained on October 30, 1995, 2:15 UT from the Calar Alto Observatory site, using a f=55mm 1/4.0 lens and Kodak Ektachrome 400 Elite film; exposure time was 40 min.

In John Caldwell's observing list. Caldwell 41 in Patrick Moore's list.

Observing Reports for the Hyades - Mel 25 (IAAC Netastrocatalog)

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Hartmut Frommert
Christine Kronberg
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Last Modification: January 11, 2001