After Dark in Allenspark	by Leslie Young

We see a lot of Subarus with their starry logos, on the streets in
Boulder county. This month, and for the rest of the winter, we can see
the original starry Subaru in the sky. "Subaru" is the Japanese name for
the cluster of stars we call "the Pleiades" or "the seven sisters." This
collection of stars looks like a "mini big dipper," about 2 degrees
across. It rises in the NNE at 7:30 PM on OCTOBER 1. By OCTOBER 31, it
rises at twilight (~5:30 PM), and is highest in the sky (74° above the
horizon) at ~1:00 AM.

With our naked eye, we see about six stars in the Pleiades under usual
conditions, and up to a dozen under clear, dark skies. (The evening sky
will be moonless, and darker, in the beginning of the month). A
telescope reveals up to 500 stars in the Pleiades.

[PLACE FIGURE HERE]

The stars in the Pleiades form an open cluster, a swarm of stars that
formed at the same time, and are held together loosely by mutual
gravitational attraction. Early last century, open clusters helped
astronomers decode the life cycle of stars. When we look at stars, we
only see two dimensions‹we can't see the third dimension, distance. A
star might be bright because it's close and intrinsically dim, or far
away and intrinsically bright.

But we know the stars in open clusters are all practically the same
distance from us, and practically the same age. So, if one star in the
Pleiades is brighter than another, it's because it really is putting out
more energy. Using open clusters like the Pleiades, astronomers figured
out that, for most of a star's life, hot blue stars put out more energy
than cooler red stars.