A large, V-shaped open cluster in Taurus, spanning over 5° of sky. It contains about 200 stars, and is estimated to be 660 million years old. The cluster lies 150 l.y. away, and its true diameter is about 15 l.y. Comparison of the brightness of its stars with those in other clusters enables the distances to those other clusters to be calculated. The Hyades is thus an important yardstick in astronomical measurement.