This is the Skywatch Line for Monday and Tuesday, September 24th and 25th. The Sun sets at 6:49 PM; night falls at 8:23. Dawn begins at 5:11 AM and ends with the Sun rising at 6:46. Note that since the Equinox happened on Sunday, the amount of daylight is now less than 12 hours.
The evening planetary parade continues. Venus, in Virgo, hovers 3º above the western horizon. Binoculars reveal it about 23% lit and blazing at minus 4th magnitude. Venus sets at 7:41 PM.
Jupiter continues to reside in western Libra and shines with minus 1st magnitude. It still appears relatively large in our instruments with 33 arc-seconds in size. The giant planet sets at 8:51 PM.
Still moving East, Saturn, in southern Sagittarius, shines with zero magnitude and appears about half of Jupiter’s size. Evening is the best time to appreciate its beautiful ring system, since it sets at 11:24 PM. Saturn is also at Quadrature, which means that it is 90º east of the Sun and the Sun’s angle makes the rings seem even more glorious.
Mars resides in southeastern Capricornus and shines with minus 1st magnitude. It appears almost as large as Saturn in our telescopes and is about 90% illuminated. The Martian dust storm continues to abate, providing improving views of surface features. Astronomical media provide charts, which identify those features. Mars is best observed at 9:08 PM and sets at 1:37 AM.
The Venus-Jupiter-Saturn-Mars group spans about 85º degrees during twilight.
Neptune, in Aquarius, is already risen, shines with 7th magnitude and is 11º high in the East. It is best observed at 11:44 PM and sets at 5:20 AM. Uranus, in Aries, glows brighter with 5th magnitude and is slightly larger, about 4 arc-seconds in size. It rises at 7:48 PM and is best examined at 2:38 AM. Both planets require detailed charts from astronomical media.
The variable star Algol, in Perseus, dims at 4:09 AM on Tuesday. The cycle begins 2 hours in advance and ends 2 hours after minimum. However, the brilliant Moon may hinder observation.
The Moon rises in Pisces at 7:02 PM on Monday, and in Cetus at 7:29 PM on Tuesday. The Moon turns full at 11:52 PM on Monday. This is the famous Harvest Moon, defined as the Full Moon nearest the Autumn Equinox. The Harvest Moon is special because the fall harvest could be conducted without daylight. Usually the Moon rises about an hour later each night. However, due to the shallow Moon’s path in the sky, called the ecliptic, this time of the year has the Moon rising between twenty minutes and a half hour later. This effect becomes more noticeable as you head to more northern latitudes. Pre-tractor farmers had the Moon to work by. This grace period lasts only until the moonrise gradually lengthens to its average interval of about 75 minutes.
Astronomers are not the only observers of the night sky. The Harvest Moon also provides bird watchers with plenty to document. This time of the year, birds start heading south for the winter. They fly mainly at night to conserve energy and avoid predators. It is not unusual to witness flocks flying across the Moon’s disk, and now is the best time, weather permitting.