The Hyades, Melotte 25

Open Cluster Melotte 25

(= Collinder 50 = Caldwell 41)

in Taurus

The Hyades

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

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.

In John Caldwell’s observing list.

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Hartmut Frommert

([email protected])

Christine Kronberg

([email protected])

Last Modification: 8 Mar 1998, 19:55 MET