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 660 million years age, therefore it is concluded that this cluster is 660 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.

The Hyades are known prehistorically. They were perhaps first cataloged by Hodierna in his 1654 publication and later by Melotte in 1915 (as Mel 25).

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 lightyears, 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 (spider@seds.org)
Christine Kronberg (smil@lrz.uni-muenchen.de)

Last Modification: 11 Jan 2001, 12:00 MET