Star Points for September, 1999; by Curtis Roelle Would the Real North Star Stand Up? Another Summer is preparing to sneak away into Autumn. For many this weekend of Labor Day is the traditional end of Summer. Kids are back in school, the swimming pools have closed, and the beach vacations have ceased. Happily the task of time keeping is handled by astronomers. This means Summer gets a reprieve until 7:30 a.m. on September 23 when the Sun slips south of the Equator marking the start of Autumn in the northern hemisphere and Spring in the southern. If the daytime heat fails to do so then a quick glance at the night sky will convince you that we are still in the thick of Summer. But more about that later. Speaking of Summer vacations this year we traveled westward by rail on Amtrak's Capitol Limited and California Zephyr lines. During a five hour layover at Chicago's Union station the family piled into a cab for a trip to the world famous Adler Planetarium on the shore of Lake Michigan. For my souvenir I picked up a copy of Richard Hinckley Allen's classic book "Star Names: Their Lore and Meaning," a 1963 edition of the original book by G. E. Stechert published 100 years ago in 1899. In future columns I will share some of the information from this informative volume. Now back to the late Summer sky. For me the ultimate sign of waning Summer is the appearance of Orion the Hunter in the pre-dawn sky. If you're looking for a sign that doesn't require you to set an alarm clock then just step outside after evening twilight around 9:00 p.m. on any night in the first half of September. The brightest star currently visible in the sky will be directly overhead. Indeed it will be within one degree of the zenith as observed from central Maryland. Vega is one third of a widely spaced group of three stars known as the Summer triangle. The other two are Deneb in the constellation Cygnus the Swan and Altair in Aquila the eagle. Deneb is about 20 degrees east of Vega and Altair is 30 degrees south-southeast. The width of your fist at an outstretched arm is roughly 10 degrees. According to Allen's book Vega used to be the north star long ago. For the rest of this year we must endure the tiresome prattle of the looming end of the 2nd millennium of our calendar as if in some short sighted way it is somehow significant in the greater scheme of things as if time had its beginning just 2,000 years ago. Yet 14 millenniums ago Vega sat near the location currently occupied by the star Polaris marking the north celestial pole. As the Egyptians were building their pyramids the Babylonians knew Vega by the name Dilgan, the messenger of light. To the Assyrians Vega was Dayan-same, the "judge of heaven" occupying the highest seat in the heavens. While the stars slowly change positions over the course of thousands of years this is not what causes such large shifts in the north celestial pole. The name of this phenomenon is "precession." Precession is caused by a long period wobble in the Earth's rotation. The typical anecdote for describing precession is a spinning toy top. Even though the top remains stable while spinning rapidly, it's spin axis slowly revolves and traces out the shape of a cone. Precession is nothing new and was first discovered by Hipparchus in the 2nd century B.C. It takes 25,800 years to complete one precessional cycle. As the Earth's axis precesses other bright stars will just happen to occupy the north pole position. Thuban, in Draco the dragon, was pole star in 2600 BC. Polaris, our current pole star, will reach its closest point to the pole a little over 100 years from now. It's already within one degree of the true pole. Taking a look into the future Cepheus' Alderamin will be pole star in 7600 AD. Vega makes a comeback occupying the ancient Assyrian seat of judgement in the year 14,800 AD. Finally, if we can make it beyond the year 2000 babble for another 26 millenniums, Earthlings will again look up and see the stars wheeling daily around Polaris at the hub of the north celestial pole.