This is the Skywatch Line for Monday and Tuesday, August 19th and 20th, written by Joe Slomka.
The Sun now sets at 7:51 PM; night falls at 9:37. Dawn breaks at 4:20 AM and ends with the Sun rising at 6:07.
The giant planets Jupiter and Saturn continue their solitary presence in our evening sky. At Civil Dusk, Jupiter still inhabits the constellation Ophiuchus, blazing at minus 2nd magnitude and about 25º high in the South; it sets a half-hour after midnight. The planet is nearing the end of its appearance, so events on the planet become rare, due to its low altitude. On Monday evening, the moon Io begins its crossing the planet’s face at 9:49 PM; Io’s shadow follows at 11:10 PM. Io ends its trek at Tuesday Midnight, but the planet is only 4º high above the southwest horizon.
Saturn trails Jupiter by about 2 hours. At Civil Dusk, it shines in Sagittarius with zero magnitude, appears about 18 arc-seconds in size and is about 20º high in the South. It is highest, and best observed, at 10:06 PM; its famous rings are still worth observing about this time. Saturn sets at 2:39 AM.
Nightfall also reveals the Dwarf Planet 1Ceres, still in the head of Scorpius, glowing with 8th magnitude and appearing one half arc-second in size. 1Ceres sets at 11:48 PM.
Outer planet Neptune rises in Aquarius at 8:38 PM and is best observed at 2:19 AM, when it is 32º high in the South. It twinkles with 7th magnitude and appears a tiny 2 arc-seconds in size. Uranus rises in Aries about two hours after Neptune. It appears brighter and a bit larger than Neptune and is best observed at Dawn. Finder charts for 1Ceres, Uranus and Neptune are available from astronomy websites and magazines.
The 19-day-old Moon rises in Cetus at 10:06 PM, Monday. It displays an 81% disk, blazes with minus 11th magnitude and is highest at 4:22 AM. Tuesday finds it in Pisces, thinner and slightly dimmer, rising at 10:30 PM. The Moon lies approximately 7º below Uranus at about 4:20 AM, Wednesday.
The variable star Algol, in Perseus, reaches its minimum at 10:04 PM on Tuesday; however, it lies only 9º high above the eastern horizon, and may require an unobstructed horizon.
Midnight witnesses the rise of two star clusters: the Pleiades and the Hyades. The Pleiades rise first and resemble a mini dipper, while the Hyades, rising an hour later, form the head of Taurus, the Bull. In Greek myth, the Hyades and Pleiades are related, both daughters of Atlas and Aethra – both seven in number. The name Hyades derives either from the story of the sisters mourning the death of their brother Hyas, or from the Greek verb “to rain,” since the Hyades’ rise signaled the rainy season. They were placed in the sky as a reward for babysitting the infant god Bacchus. The Hyades is the second closest cluster to Earth, second to the Ursa Major cluster. It is about 400 million years old. This cluster is about 150 light-years away and part of the “Taurus Moving Cluster” of stars that are heading towards the star Betelgeuse. The bright star Aldebaran is not a member of this group, and actually midway between Earth and the Hyades.