Star Points for September, 2003; by Curtis Roelle Mars' Curtain Call Earth is now pulling ahead of Mars in the perpetual race around the sun thanks to its "inside track" advantage. On average the Earth is 49 million miles (78 million kilometers) nearer to the sun than Mars. Lucky for us Mars remains well placed for telescopic observing during September. Throughout 2003 both planets are located on the same side of the sun. As mentioned last month, on August 27 Mars and Earth were closer together than they have been in some 60 thousand years. From that date until the end of September the diameter of Mars' visible disc shrinks by 17 percent. Even then its apparent size will be larger than the maximum size achieved during the favorable 2001 opposition. The best time to see Mars is an hour or so before and after "culmination" - when Mars crosses the meridian and is positioned due south at it's highest point in the sky. At the end of August Mars was culminating at around 01:00 a.m. EDT. Another September advantage is Mars will be well placed during more "normal" hours. By the end of the month culmination occurs around 10:45 p.m. EDT. As far as their orbits go distance from the sun is not the only difference between the Earth and Mars. The shapes of their orbits are also quite different. The characteristic that describes the shape of an orbit is called the "eccentricity." Eccentricity is a number between zero and one. A circle has an eccentricity of 0.0. Earth's orbital eccentricity is 0.017 - nearly circular. However, this value stretches to 0.093 for Mars. What this means for Mars is that its distance from the sun varies during the course of its orbit by 26 million miles (42 million km) according to the 4th edition of George Abell's "Exploration of the Universe". As the solar distance varies so does the energy that Mars receives from the sun. This leads to changes in the temperature of the thin Martian atmosphere in ways that are visible in telescopes. The best example is the shrinking and expanding of the polar ice caps on Mars. Another is the regional and global dust storms that are kicked up by the planet's shifting winds. The reason I mention dust storms is that global planet-shrouding dust storms traditionally occur near the time of Mars' closest approach to the sun (perihelion). In 2001 a global dust storm kicked up just days after opposition and lasted for weeks. By the time it cleared Mars' disc has shrunk considerably due to its increasing distance from us. At other favorable oppositions, which occur every 15 or 17 years, there have been global dust storms in 1971 and 1956. According to the September Sky & Telescope magazine the season where a dust storm will be most likely begins on September 6. This date is based on empirical data. Another opportunity for dust storms may begin on December 13. Of course, by that time the disk of Mars will have shrunk to less than half the size it will be at the end of September. So keep Mars in mind and in your telescope view while you can. Soon it will shrink so much that detail will be hard to see. Also, you never know when a Martian storm will draw closed a dusty curtain and end the party. If you haven't seen Mars and would like to, the next opportunity for public viewing will be on Friday, October 3. Members of the Westminster Astronomical Society Inc. (WASI) will have telescopes set up at the Bear Branch Nature Center (BBNC) north of Westminster (weather permitting). There will also be two rain or shine planetarium programs that evening at 07:30 and 08:30 p.m. The star party begins at 07:30 p.m. and is free. For planetarium reservation information, please call BBNC at 410-848-2517.