Program for Starry Night II

May 14, 2002

(rain/cloud date May 16, 2002)

8:15-8:45pm. Short Presentation

9:00 – 10:00pm. Telescope Viewing

What exactly we will be looking at will depend on the sky, the equipment available, etc. Here are some of the things we will try to see. Included are links to more information as well as photographic images of the objects. It is well worth looking at these, since they give an idea of what one should look for. On the other hand, it is important to realize we will not look like these images. The planetary images, of course, were taken at close range from spacecraft. The images of more distant objects represent long exposures (15 minutes or more). Collecting light for this long yields contrast levels we cannot expect, so what we will see will be pale and hazy suggestions of the shapes in the images.

1. Planets: As you may have heard, the five visible planets are in conjunction now and all visible at the same time just after sunset in the western sky. This is best viewed with the naked eye in a location with a low, dark, western horizon. The trees at our observatory will make seeing Mercury difficult. We may try to catch a glimpse of Venus. Since this planet is nearer the sun than Earth, it exhibits phases, just like the moon. Venus should be about 85% full, and if it is not obscured by trees we should be able to see this. For more sophisticated images of Venus taken by some of the NASA craft to orbit it, try here. We will certainly take a look at Jupiter, the largest planet, bright and prominent. We should be able to see some of its four Galilean moons, and hopefully some surface features on the planet, including the Great Red Spot, a storm system the size of Earth. What we see may look like this. Really amazing pictures of Jupiter are here.

2. Stars: Looking at a star with a telescope is not really that exciting. With a telescope we can see many stars far too faint to be visible to the naked eye, but even the nearest stars are too distant for our telescopes to resolve their shape or structure. It is sometimes fun to enjoy the variety of colors we can see. We will probably focus on looking at some multiple stars – “stars” that are in fact several objects too near in the sky for us to resolve. In a multiple star system the various stars orbit the common center of gravity much as the planets orbit the sun. (When there are two such objects we speak of binary stars.) Some 50% of all stars are probably bound in such systems. With a telescope we can resolve the image into its component objects. A famous example we may see is Mizar in the Big Dipper, the first binary found (in 1650). The two stars orbit each other at a distance some 500 times the Earth-Sun distance every 5000 years. In fact, each of the two stars into which we resolve Mizar is itself a binary, so the system is a quadruple star, a double-double. Using a sophisticated interferometer, the brighter of the two, a double with an orbital period of 20.5 days, has been “resolved,” see the picture. In some cases, the two stars that make a binary differ in surface temperature, hence in color. The resolved view is then striking. We will try to find such a binary, perhaps 95 Hercules, whose two component stars are variously reported to appear green/red and gold/silver. Let’s see what we think!

3. Star Clusters: We will look for some bright clusters of stars. M13, the Great Hercules Globular Cluster, is a dense collection of hundreds of thousands of stars, located some 25,000 light-years away. Globular clusters are among the oldest structures in the universe. M13 is estimated to be 14 billion years old.

4. Galaxies: Some of the most exciting objects to view with a telescope are the many objects outside our Milky Way galaxy that we can observe. We will look at several galaxies. Some of these are bright enough to be visible to the naked eye; in some cases a careful observer will even note that the objects seem “diffuse.” With the telescope we will get images that let us note the shape of the object. Galaxies, like stars, are found in clusters or groups. We will look at the M81 group in the Big Dipper, some 12 million light-years away. Here we may see Bode's galaxy M81, a classic spiral discovered in 1774, and its companion the cigar galaxy M82. The irregular shape of the latter, as well as some recently formed active star clusters in it are attributed to a recent (50-100 million years ago) near-collision with M81. A picture of both with their relative positions may look like this or this. We will also likely look at the famous Virgo cluster of galaxies, some 60 million light-years away. This huge cluster (some 2000 galaxies) is the center of the local supercluster, which includes the Local Group of which our Milky Way is a member. So powerful is the gravitational attraction of the Virgo cluster, that it is estimated that our local group will eventually be attracted to it and absorbed. Of the Virgo galaxies we may be able to see the huge elliptical M87 and the bright spiral M100, or the Sombrero galaxy M104.