Hyades

(astronomy) A V-shaped open star cluster about 150 light-years from the sun, which appears in the constellation Taurus near the star Aldebaran.

A small cluster of stars that makes up the nearest well-defined open cluster (galactic cluster) to the Earth. With a total mass of about 300 suns and a population of 400–500 mostly low-mass stars, the Hyades is a typical example of the 2000 or so small star clusters in the Milky Way Galaxy. Most of its stars are located in a loose, roughly spherical system approximately 40 light-years (2.4 × 10¹⁴ mi or 3.8 × 10¹⁴ km) in diameter. It is located primarily in the constellation Taurus, the Bull.

For many years the Hyades was the backbone of the stellar distance scale in the Milky Way Galaxy and beyond. However, in 1967, evidence was found suggesting that the distance to the Hyades (and, therefore, almost all other distances in the Milky Way Galaxy and beyond) had been underestimated by 20%. This conclusion was confirmed in 1996, when the European space telescope Hipparcos was able to make a more direct and more precise measure of the Hyades distance of 149 light-years (8.7 × 10¹⁴ mi or 1.4 × 10¹⁵ km). See also Astrometry; Parallax (astronomy).

The age of the cluster is approximately 6.5 × 10⁸ years. Thus the Hyades were formed quite recently, after about 95% of the life of the Milky Way Galaxy had already occurred. See also Milky Way Galaxy; Star clusters.