Star Points for May, 2007; by Curtis Roelle How Big is the Galaxy? Last month we talked about a scale model of the solar system. In our model Pluto's orbit was 800 feet across. Let me add that at this scale Proxima Centauri, the nearest star to the sun, is 511 miles away. If the sun was in Westminster, its closest stellar neighbor would be in Detroit, Michigan. This month we expand our model outward and tie it to other models developed for NASA's Night Sky Network (NSW) to be used by amateur astronomy clubs, such as the Westminster Astronomical Society, Inc. (WASI), when talking with the public about space. First we need to scale back our model before pushing onward to ever greater distances. Light travels at 186,000 miles per second or about six trillion miles per year. Even at this break neck speed it takes light 11 hours to cross from one side of Pluto's orbit to the other. In other words, our solar system (i.e. Pluto's orbit) is 11 light- hours across. We now reduce our model to a smaller size. Instead of 800 feet the solar system will now be just two inches across. The distance from the sun to Pluto to about the diameter of a U.S. quarter coin. In our new scale two inches represents a distance of 11 light-hours. One mile is a distance of 40 light-years. At a distance of 4.3 light-years, Proxima Centauri is just over 1/10 of a mile from the sun. But at 430 light-years the north star (i.e. Polaris) is 11 miles away -- about the distance between Westminster and Taneytown. All of the stars we see in the sky are located inside our own Milky Way galaxy. In fact, most stars we see are in our own immediate neighborhood and relatively nearby. The Milky Way galaxy is estimated to be 100,000 light-years across. That is, light takes 100,000 years to traverse the galaxy from one edge to another. In our two inch solar system model the galaxy is as wide as the United States -- about 2,500 miles across. Our galaxy is thin. Although 100,000 light-years across it is only about 1,000 light years thick. Thinner than a pancake! In our model the galaxy is only 25 miles thick. Would you like to go out even farther? If so, then we need to reduce our scale even more using familiar objects from another NSN model. Let's reduce the scaled size of the whole Milky Way galaxy from 2,500 miles across in our present model to the size of a CD- Rom or DVD disc. We should note here the location of our solar system in the DVD- sized galaxy. Our earth and sun are located about halfway from the center to the outer edge of the disc. At this latest scale four feet represent one million light-years. Galaxies come in different types and our Milky Way is a spiral type of galaxy. The nearest spiral galaxy to us is the Andromeda Galaxy, or Messier 31, located more than two million light years from us. In our model Messier 31 is represented by a salad plate a little more than eight feet away from the Milky Way. The Milky Way and Andromeda are the two dominant galaxies of our local group of galaxies. Other groupings and clusters of galaxies, such as the Virgo cluster, together form a local super cluster of galaxies known as the Virgo supercluster. The most dominant galaxy in the supercluster is the spherical giant M87. In our model M87 is the size and shape of a softball 80 yards out from the Milky Way. We could go on and on like this but I think you get the idea. I just wanted to talk about the size of our local space neighborhood in familiar terms and to share a sample of the kinds of ideas coming out of programs being produced by the NSN program. The next opportunity for you to visit the planetarium at Bear Branch Nature Center (BBNC) is at 07:30 p.m. Saturday, May 26. Weather permitting, WASI will host an outside "star party" with telescopes. The star party is free and the planetarium program is rain or shine. For planetarium directions, reservations and pricing call BBNC at 410-848-2517.