Thanksgiving Holiday Serves Up Star Clusters for Skywatchers
Here are some of the beautiful open star clusters which grace the autumn skies.
Credit: Starry Night Software [Full Story]

The Thanksgiving holiday in the United States is a great time to gaze at the many brilliant open star clusters that grace the late autumn skies in the Northern Hemisphere.

The Milky Way rises above the eastern horizon, laced with the finest clusters visible to the naked eye, binoculars, or small telescopes.

The brightest of all star clusters ? in fact, the brightest deep sky object in the entire sky ? is the Pleiades, also known as the Seven Sisters, or, in Japanese, "Subaru."

Yes, the Japanese car manufacturer is named for this famous star cluster, as is the giant Japanese telescope atop Mauna Kea in Hawaii. The Pleiades consists of about 800 bright young stars, with a surprising number of older white dwarf stars mixed in.

This sky map shows how to spot the Pleiades in the night sky.

Blazing bright Pleiades

The Pleiades is bright for two reasons: its relatively young age and its close distance to us, approximately 410 light-years.

The star cluster's brightness of 1.2 magnitude places it among the 20 brightest objects in the sky, easily seen without aid. Astronomers measure the brightness of objects as magnitude. The lower the magnitude number, the brighter an object is.

How many stars can you see in the Pleiades with the naked eye?

Although the name "the Seven Sisters" suggests seven stars are visible, most people can see only six. (The Subaru automobile logo shows six stars.) Even the smallest binoculars will reveal dozens more.

If you are graced with really dark skies, you even may see the faint wisps of the gas and dust that surround these stars.

More star clusters in sight

The Pleiades is only one of many rich open clusters in this part of the sky.

Open clusters are relatively small groups of relatively young stars embedded in the Milky Way galaxy, in contrast to globular star clusters, which are much larger groups of very old stars in orbit around the center of the Milky Way.

Just below the Pleiades, still in the constellation of Taurus, is a closer and more scattered cluster, the Hyades. Only 150 light-years away, this is the closest star cluster to the sun.

The bright red giant star Aldebaran appears to be part of this cluster, but in fact it is much closer to us, only 65 light-years away, so its presence in the Hyades is just an accident of perspective.

Many of the stars that make up the constellation of Perseus, just above Taurus, are members of another star cluster, named after its brightest star, Alpha Persei (also called Mirfak).

At 600 light-years away, the Perseus Moving Cluster is slightly farther away from us than the Pleiades or Hyades. It?s called a "moving cluster" because its stars share a common motion across our sky. The Hyades is also a moving cluster, but the Pleiades is not.

Telescopes out for some targets

All the nearby star clusters mentioned so far are best viewed with the naked eye or low-power binoculars. The remaining clusters in this area are best appreciated through binoculars or a small telescope.

The Perseus Double Cluster, located halfway between Cassiopeia and Mirfak, is actually two star clusters, located 7,000 and 8,100 light-years away but almost aligned in our line of sight. The two clusters are very different in the density and color of their stars, and make a beautiful contrast on a clear crisp autumn night.

To the left of Taurus and below Perseus is the rough hexagon of Auriga, dominated by the brilliant first-magnitude star Capella.

This is in one of the richest areas of the Milky Way, abounding with beautiful star clusters best explored with a small telescope. Three of the most famous were cataloged by comet-hunter Charles Messier in September 1764 after being discovered by Sicilian astronomer Giovanni Battista Hodierna over a century earlier. M36 and M38 are inside the hexagon; M37 just outside.

Just to the left of Mirfak and just below Cassiopeia lies a strange constellation with a tongue twister of a name: Camelopardalis. This constellation, named after the giraffe, contains no bright stars and is often overlooked by stargazers.

It does contain, however, one of the loveliest objects in the sky, Kemble?s Cascade.

This is not a true star cluster, but rather an asterism ? a grouping of stars that lie in the same direction but are not physically connected. It is a chain of about 20 stars of similar brightness that  seem to tumble across the field of a binocular. It is named after its discoverer, Canadian amateur astronomer Father Lucian Kemble (1922?99).

The objects described here are just a jumping-off point for the exploration of one of the richest and most rewarding areas of the sky.

This article was provided to by Starry Night Education, the leader in space science curriculum solutions.