September: Planets and Lagoons

September 2008

Planets and Lagoons

By Calvin L. Chrisman

September marks the arrival of autumn in the Northern Hemisphere. Astronomically speaking, it will happen at 11:44 a.m. Eastern Daylight Time on Monday the 22nd. This is called the Autumnal Equinox when the Sun crosses the equator on its journey south. As the month progresses, we will steadily lose daylight. At the Equinox, the day will have over an hour less daylight than a month ago.

September offers some interesting sights. During the month, the planets Mercury, Mars and Venus will be following the setting Sun in the western sky. Perhaps the best sight will be about 30 minutes after sunset on September the 18th and 19th when the first magnitude star, Spica, will join these planets to form a trapezoid that should be visible with hand-held binoculars. This sight will continue through about the 26th, but Mercury will fade quickly as it sets earlier and earlier. Another member of this trio, Venus, will be moving higher in the sky during this period and will set an hour after the Sun at the end of the month. Many people know it as the “Evening Star” and it will continue to brighten in the coming months.

While you have your binoculars out, you might want to try and see a “deep sky” object known as the Lagoon Nebula or M8. The “M” in M8 refers to Charles Messier, an eighteenth century astronomer who was a comet hunter. He began cataloging faint objects such as M8 so that he would not confuse them with comets. Some of the most famous Messier objects include the Pleiades (M45), and the Andromeda Galaxy (M31). M8 can be found in the constellation Sagittarius a short distance to the right of the planet Jupiter which we discussed last month. If you want to get a clearer idea of where to look, many on-line sky maps, such as that offered by Sky & Telescope Magazine can give you a precise idea of where to aim your binoculars or telescope. The Lagoon Nebula gets its name from the dark dust lane down its middle, giving the appearance of a lagoon between two illuminated shores.

Another interesting sight to look for in September will be a bright and high pass over Black Mountain by the International Space Station on the early evening of Friday, September 12th. The pass will occur over about six minutes (the ISS takes only about an hour and a half to circle the globe), so be sure to get ready ahead of time. It will begin at 6:46 PM in the northwest and should be visible about 10 degrees above the horizon moving toward the northeast. Remember that our mountains obscure the horizon, so be patient and sweep the sky with your eyes in that direction. Once you pick up the ISS, it will be easy to track. It will reach its highest point in the sky at 6:49 PM and will be about 65 degrees above the horizon in the northeast. At magnitude -1.9, it will be easily visible. It will fade in the southeast at about 6:52 PM. If the sky is cloudy or you forget to go out, an even brighter and higher pass will occur two days later on Sunday, September 14th starting at 6:05 PM and lasting until 6:10 PM. It will follow the same path.

Clear Skies!

Leave a Comment