RIT Observatory Public Night

Sep 23, 2005

You can find this page on the Internet at

http://spiff.rit.edu/richmond/ritobs/public/sep23_2005/sep23_2005.html

Tonight is one of the rare dark, clear nights in Rochester. We will take advantage of the good conditions to ask you three questions:

  1. Can you see the Milky Way?
  2. Can you any GLOBULAR clusters?
  3. Can you see any OPEN clusters?

Can you see the Milky Way?

On the next page of this handout is a chart showing a view of the entire sky tonight at around 9:00 PM. If you stand outside looking south, then hold this page over your head, it should match the sky.

Go outside onto the concrete pad and give your eyes at least 10 minutes to adjust to the dark. Can you make out the Milky Way? If you have very sharp eyes, or if you go do a very dark site, you should be able to see the dark rift or break in the Milky Way almost overhead, in the constellation Cygnus.

The set of 3 bright stars nearly overhead is called the "Summer Triangle". Near the horizon in the northwest sky (in the direction of the RIT campus) is the Big Dipper. Use these asterisms to orient yourself, then try to find the constellations shown on page 3 of this handout. How many can you find?

The two types of star clusters

Our galaxy contains two very different types of star clusters.

Globular Clusters
are very old, very dense swarms of tens of thousands of stars. Most were formed long ago, perhaps 10 billion years ago. By now, all the massive stars have used up their nuclear fuel and died, so that the only ones left are about the mass of our Sun or less. Globular clusters are so dense that may look more like a fuzzy ball than a collection of thousands of points of light:

Open Clusters
are much younger: most are only millions, not billions, of years old. They are composed of stars which only recently collapsed from a single giant cloud of gas and dust. The most massive of these young stars may be ten or thirty times as massive as our Sun, and so hot that they look blueish-white. Open clusters appear more like loose collections of stars than tight balls, and indeed the stars are packed much less tightly in space.

On the back of the last page is a portion of tonight's sky with the locations of a number of star clusters marked by circles. We will point our telescopes to some of these clusters during the Open House. Can you figure out which type of cluster is at each location?

For more information