Thursday, August 27, 2009

September Skies Full Of Surprises

By Jon Spargo
Tech Astronomy Club
Jupiter, just past opposition, will provide us with a very unique opportunity on the night of September 2-3 here in North America. Between the hours of 10:43 pm and 12:29 am MDT all four of Jupiter’s Galilean moons will be invisible! This is because they will either be in front of or behind the giant planet. Io and Callisto will be behind Jupiter while Europa and Ganymede will pass in front. This is the last time this will happen until 2019!
The phrase that best describes Saturn’s appearance this month is going, going gone! Barely 5 degrees above the western horizon at the beginning of the month, Saturn will be tough to find in the glare of sunset. If you have a good sized telescope and get lucky you may be able see the rings edge on as the Earth crosses the ring plane on the 4th. This is the first time this has happened since 1996 and the last time until 2025. Try finding Saturn about 15 minutes after sunset.
Mercury will be about 13 degrees to the left of Saturn at about the same elevation above the horizon. Both Mercury and Saturn will be visible for the first few days of the month. Both are heading for conjunction with the Sun and will next appear in the morning sky.
Nothing much changes for Mars as it will rise around midnight. During the course of the month its brightness will increase slightly from magnitude +1.0 to +0.8. Mars can be found in the constellation Gemini and will approach the bright star Pollux by the end of the month. Venus, blazing away at magnitude -3.9, rises about 3 hours before sunrise. On the 20th it will be only ½ degree north of the bright star Regulus in the constellation of Leo the Lion.
Many times it is difficult to estimate just how close or far objects are from each other or from the horizon. There is an easy and useful trick you can use to determine the angular distances involved. Make a fist and hold it at arms length in front of your eyes. The width of your fist at that distance will equal about 5 degrees. This works for everybody because it turns out that the ratio of the size of the fist to the length of the arm is about the same for all people, regardless of size.
The Moon will be full on the 4th, last quarter on the 11th, new on the 18th and 1st quarter on the 26th. On September 2nd the Moon will be slightly above and to the left of Jupiter. This position of the Moon will be almost exactly repeated on the night of the 29th. In the early morning hours of the13th a waning crescent Moon will be about 4 degrees above Mars and on the 16th about 4 degrees to the right of Venus.
The Sun will reach the Autumnal Equinox at 3:15 on September the 22nd signaling the first day of autumn in the northern hemisphere. Folks below the equator get to welcome spring.

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