This is Dudley Observatory’s Skywatch Line for Friday, January 11 through Sunday, January 13, written by Sam Salem.
On Friday, the Sun rises at 7:25am and sets at 4:42pm; the waxing crescent Moon rises at 10:36am and sets at 10:08pm. On Saturday evening, the crescent Moon slowly drifts south of Mars. At their closest, around 9:27pm, they’ll be separated by a little more than five degrees. Mars’ steady eastward drift has kept it near the meridian in the early evening for months.
The morning sky is home to Venus and Jupiter. Venus, at magnitude –4.5, rises a little before 4am. Jupiter, at magnitude –1.8, rises at the southeast horizon around 4:45am. Jupiter is obviously fainter than Venus, and yet it’s still more luminous than the brightest stars.
Evenings over this weekend are partly lit by the waxing crescent Moon that doesn’t set until nearly midnight on Saturday. The early winter sky is rich with bright deep-sky treasures. The Pleiades, or Seven Sisters, in constellation Taurus, is one of the few deep-sky objects that are splendid in binoculars. Also known as Messier 45 (M45), the Pleiades cluster looks like a miniature, short-handled version of the Big Dipper. The main “dipper” stars range in brightness from 2.8-magnitude Alcyone, to 4.2-magnitude Merope. In addition to the group’s main components, one feature that always attracts attention is the distinctive curving row of 7th- and 8th-magnitude stars leading into Alcyone from just below the tiny dipper’s stubby handle. All this is set against an attractive scatter of faint stellar glints throughout the field. It’s a wonderful sight in any pair of binoculars. If you’re observing M45 under a very clear, dark sky, try to catch sight of the nebulosity near Merope. This weekend, you’ll have to wait for the Moon to set before making your attempt. In binoculars the glow resembles a faint, broad comet tail extending south from the star. A small, low-power scope also shows this feature well, though telescopes generally don’t have sufficiently wide fields of view to contain the entire Pleiades cluster. This is one celestial object binoculars really do show best.
On January 11 1787, the German Astronomer, William Herschel, discovered the first two moons of Uranus, Titania and Oberon, six years after he had discovered the planet. Titania is the largest of the moons of Uranus and the eighth largest moon in the Solar System. Its orbit lies inside Uranus’ magnetosphere. Oberon is the outermost major moon of the planet Uranus. It is the second largest moon of Uranus and the ninth most massive moon in the Solar System. Oberon’s orbit lies partially outside Uranus’ magnetosphere. Although the first two Uranian moons were discovered in 1787, they were not named until 1852. The responsibility for naming them was taken by Herschel’s son, John. Instead of assigning names from Greek mythology, John named the moons after magical spirits from William Shakespeare’s A Midsummer Night’s Dream. Titania is named after the queen of the fairies and Oberon is named after the mythical king of the fairies from A Midsummer Night’s Dream.