Marvels in Taurus
Two open clusters are prominent in the constellation Taurus, the Bull. The Hyades are the large V-shaped group of stars (lower left) with the bright non-member star Aldebaran at one end of the V. The Pleiades (M45) are the compact star group to the upper right.
Courtesy Akira Fujii.
The constellation Taurus is well placed in the evening sky. Situated along the western edge of the Milky Way, Taurus might be expected to contain swarms of open clusters that pepper the constellations of Cassiopeia, Perseus, and Auriga. But this is not the case. Yet Taurus is still an observer's paradise; objects within its borders include the magnificent naked-eye Pleiades and Hyades star clusters.
The Hyades star cluster is rather close to us, and its stars appear spread over quite a large area. Unlike the Pleiades, no nebulosity is associated with the group. In fact, whenever I think I've sighted the wispy glow between the Pleiades, I quickly turn to the Hyades to check for a glow there, too. If I see any, then I know to blame a slight dewing of the optics, even if their surfaces look clear.
Winter brings many cold but often clear nights. On such evenings, when the stars sparkle like diamonds, nothing is more spectacular than M45, the Pleiades. It's delightful in any instrument, from the naked eye to the largest amateur telescope, although I find large binoculars give the most impressive view. Almost every culture, past and present, mentions in its folklore the dazzling stars of this nearby cluster.
The incomparable Pleiades in Taurus. No other celestial configuration appears so often on the pages of the poet.
Courtesy Akira Fujii.
Have you ever tried to count the Pleiades with the naked eye? Do not consult a chart while you are trying to count them. Instead, make a careful drawing of what you see and compare it with a chart later. Depending on light pollution and sky conditions, most persons can see between four and six naked-eye Pleiads. Traditionally, the average eye can see six stars here, the exceptional eye seven. Ten bear names or Flamsteed numbers. Perhaps because it has been repeated so many times that the number of naked-eye Pleiads is six or seven, too many observers quit counting before really reaching their limit. Many observers can reach magnitude 7.5 with the naked eye. But in the sooty skies of our populated areas, it's now not uncommon that no stars can be distinguished; the eye sees just a shimmering patch. So the number of Pleiades stars visible is really an index of the transparency of the atmosphere, and the cluster does not make a valid eyesight test. If you look at this cluster only infrequently, one glance will not tell you much about the sky conditions. But with practice you'll know by the cluster's appearance whether the night is a particularly good one.