This is the Skywatch Line for Monday and Tuesday, September 12th and 13th.
The Sun sets at 7:09 PM; night falls at 8:46. Dawn breaks at 4:56 AM and ends with the Sun rising at 6:33.
The eleven-day-old waxing Moon rose this afternoon and, by 9:40 lies due South; it appears, in Capricornus, about 82 percent illuminated and blazes at magnitude minus 11. Tuesday’s Moon is 90 percent lit. The Moon sets before Dawn.
Brilliant Venus shines at minus 4 magnitude in Virgo and brightens slightly this month. Venus is only 5 degrees above the horizon, so the observer should have an unobstructed western horizon. It appears about 90 percent illuminated and sets about 8:10 PM.
The reconstituted celestial triangle of Mars, Saturn and Antares continues. Mars, in Ophiuchus, is brightest at minus magnitude 0.1. Saturn shares Ophiuchus with Mars and shines at 0.5 magnitude. Both Mars and Saturn are slowly moving eastward. Mars is 11 degrees east (right) of Saturn and also 11 degrees separated from the red star Antares. On September 13th, Mars is at “quadrature,” which means it is at 90 degrees from the Sun; as a result, it looks, through telescopes, about 85 percent lit. Mars, Saturn and star Antares all set by 11 PM.
Neptune rises in Aquarius at 6:43 PM. However, the nearby Moon’s glare may hide the 7.8 magnitude planet from view. Neptune sets during Dawn. Uranus rises in Pisces at 8:19 PM. It shines at magnitude 5.7, so it stands a better chance of being spotted due not only to its brilliance but its distance from lunar glare. It, too, remains up most of the night. Both require detailed sky charts for location.
There some objects that are perfect binocular targets. Directly overhead, the constellation Cygnus seems to fly south for the winter. Below the neck of the Swan is a small constellation – Sagitta. The Latin name means “arrow”, and that is exactly what it looks like. Sagitta is a small constellation; but it has a single deep sky object, M71. M71 is a star cluster, but 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 show that it is just a random placement of stars that happen to resemble an everyday article.