A Summer Comet
Linear 1999 S4 gives some indications that it may be the first visible comet of the 2000s. Look for the comet near the end of the June through early August. In case the name doesn't seem to be quite as euphonious as many comets of yore, blame it on the advance of technology. The LIncoln Near Earth Asteroid Research satellite was designed to locate the asteroids which approach the Earth. This satellite also is adept at detecting comets long before Earth based telescopes can peer through the murk of our atmosphere to find them. Linear has a long string of "finds" to its name, hence the additional designations of the year plus a code.Forecasting the brightness of first time comets like 1999 S4 is educated guessing at best. Many comets predicted to be spectacular have been duds. Mentioning the name Kahoutek will send prognosticators running for cover. In spite of my own warning, I will join the ranks of fearless foolish forecasters by predicting that 1999 S4 has a good chance to be faintly visible to the unaided eye and a fine object in binoculars.This sketch shows the path of 1999 S4 during July as seen from our Observatory. By 7/1 the comet will leave the Andromeda entering Perseus. On 7/8 it will be near the bright star Mirfak. From 7/21 until 7/27 you will be able to use the Big Dipper's bowl to locate the comet as shown. The comet will continue above the horizon until early August. On August 7th the bright star Spica will be just to the west of the comet. A week later 1999 S4 will be setting during twilight in the west south west.Comets are one of the celestial objects which are better seen through binoculars than through a large telescope. Comet tails are too long to be seen in a large telescope. Only the head appears in our 16" telescope. Binoculars allow you to go out on the spur of the moment if the clouds suddenly and briefly clearTry to spot the comet by eye by referring to the sketch. If this fails sweep the area near the sketch with binoculars. The comet will pass through areas which are full of galaxies. The fuzzy head of a comet and a galaxy are easily confused. Check the same place the next night. If the "comet" is in the same place, you spotted a galaxy. If it seems hopeless, come down to the Observatory and we'll try to show it to you.On the 21st of June, the Sun will move to its northernmost position, over the so called Tropic of Cancer. The Tropic of Cancer is an approximate line on the Earth which drifts as the Earth wobbles slightly. In the United States we mark this as the official start of summer, but our friends in Great Britain call this day "Midsummer's Day" .The British start summer 44 days earlier. Informally, we tend to treat the period from Memorial day to Labor Day as summer time and if you ask any school child when summer runs you'll be told from the last day of school until it resumes in the fall. Someone in Argentina would tell you that June 21st was winter.On the 21st anyone north of 67 degrees north latitude will experience the famous Midnight Sun. At the North Pole the Midnight Sun runs from March 21st and until September 21st. Even here in Rhode Island, a hundred miles or so closer to the Equator than the Pole, June 21st has a surprisingly short period of true darkness. While the Sun is below the horizon for about 9 hours only about 6½ hours are truly dark.