This is the Dudley Observatory Skywatch Line for Monday and Tuesday, September 14th and 15th written by Joe Slomka.
The Sun sets at 7:07 PM; night falls at 8:44. Dawn breaks at 4:58 AM and ends with the Sun rising at 6:35.
At civil twilight, Mercury, which has hugged the western horizon, is very low on Monday; Tuesday finds it below the horizon. Mercury will reappear in the morning sky next month.
The two-day-old Moon is slightly higher than Mercury in the West. It, too, requires an unobstructed horizon. A lucky observer will see a three percent-illuminated Moon. Tuesday finds a thicker crescent Moon higher in Southwest. The Moon sets at 7:47 PM on Monday, 8:16 on Tuesday.
Saturn is much easier to find. It shines moderately high in the Southwest between Libra and the head of Scorpius. Saturn sets earlier daily. So, an astronomer should find the planet as soon as sky conditions permit. The rings are still beautiful, but details become lost as the planet gets lower in our turbulent atmosphere. Saturn sets at 10:04 PM.
Nightfall witnesses the appearance of distant planets Uranus and Neptune. Neptune rises before sunset, and is best observed, in Aquarius, at about Midnight. Uranus rises in Pisces during Twilight, and remains up all night. Neptune sets at 5:27 AM. Finder charts can be found in astronomical magazines, websites and apps.
Venus rises in Cancer at 3:42 AM. It will be the brightest object in the sky, at magnitude minus 4.5. High powered binoculars or any sized telescope reveals it about 22 percent illuminated. Venus is at maximum brightness now and daily appears higher in the sky.
Mars, in Leo, rises at 4:06 AM and appears about ten-and-a-half degrees to Venus’ left and dimmer than Venus. Under high powers, Mars appears about 98 percent illuminated.
Jupiter brings up the rear, rising in Leo at 5:18. Jupiter is bright, at minus 1.7 magnitude, and appears large in our binoculars and eyepieces. For the rest of the year, it flies in formation with Mars and Venus, and forms a conjunction with Mars on October 17th and Venus on October 26th.
Some objects are perfect binocular targets. Overhead, the constellation Cygnus seems to fly south for the winter. Below the Swan’s neck is a small constellation – Sagitta. The Latin name means “arrow”, and that is exactly what it looks like. Sagitta is a small constellation, and has a single deep sky object, M71. M71 is a star cluster of uncertain type. It displays characteristics of both globular and galactic clusters. It is about 18,000 light years distant, and 30 light-years wide. The binocular observer should see a fuzzy glow about halfway along and a bit below the arrow’s shaft.
Just above the “Arrow’s” tail feathers is a curious object. The Coathanger is an asterism – an image of stars, but not a constellation. This is a perfect binocular target, since a telescope’s magnification destroys the illusion. The Coathanger also goes by the names: Collinder 399 and Brocchi’s Cluster. However, the Coathanger is not a true cluster. Hipparchos satellite measurements reveal that it is just a random placement of stars that happen to resemble an everyday article.
At 7 PM on September 15th, Dudley Observatory will hold its monthly Night Sky Adventures. This month’s event will preview the lunar eclipse of September 27th.