This is Dudley Observatory’s Skywatch Line for Friday, January 21, through Sunday, January 23, written by Sam Salem.
On Friday, Sun rises at 7:20am and sets at 4:54pm; Moon sets at 9:38am and rises at 8:45pm.
Venus, at magnitude –4.3, emerges into dawn view. Look for it low in the east-southeast about 45 or 30 minutes before sunrise. It gets higher every day. In a telescope or good binoculars, it’s a thin crescent, getting thicker every day.
Mars, fainter at magnitude +1.5, is low in the southeast in early dawn. If Venus has risen at the time of observation, it sits some 20 degrees to Venus’s upper right. Mars-colored Antares sit to Mars’ upper right. Mars and Antares are 19 degrees apart on Saturday morning. Mars is on the far side of its orbit from Earth. In a telescope it’s just a tiny blob 4 arcseconds wide.
Jupiter, at magnitude –2.1 in Aquarius, still shines brightly in the southwest at dusk. It sits lower every week.
The asteroid 7 Iris, at magnitude 7.8, is just a week past opposition and nicely placed high in Gemini by 8pm. It sits under the Pollux stick-figure twin, and above Procyon, the brightest star in the constellation of Canis Minor.
In mid-evening during late January, the Pleiades open star cluster, also known as the Seven Sisters and Messier 45, is positioned high in the southern sky. The rest of its home constellation Taurus sits below the cluster. The Pleiades is composed of the medium-bright, hot blue stars named Asterope, Merope, Electra, Maia, Taygeta, Celaeno and Alcyone. In Greek mythology, those characters were the daughters of Atlas, and half-sisters of the Hyades. The stars of the Pleiades are indeed related, recently born of the same primordial gas cloud. To the naked eye, only six of the sister stars are usually apparent. Their parents Atlas and Pleione are huddled together at the east end of the grouping. Under magnification, hundreds of stars appear.
The Double Cluster is composed of the two large and bright open clusters NGC 884 and NGC 889. It sits high in the northern sky after dusk in winter, then descends to skim the northern horizon by dawn. Try to split the pair of clusters, each as wide as the Moon and almost a lunar diameter apart with unaided eyes. Binoculars or a low power, wide-field telescope will show them in more details. NGC 869, the more westerly cluster, is more compact and contains more than 100 white and blue-white stars. NGC 884, the easterly cluster, is much less compact. It hosts a handful of 8th magnitude golden stars. Use higher power to see doubles, mini-asterisms, and dark lanes of missing stars. The two clusters are inside the Perseus Arm of our Milky Way galaxy, about 7,300 light-years from the Sun. Their visual brightness has been dramatically reduced by opaque interstellar dust in the foreground.
On Friday, the waning Moon doesn’t rise until about 9pm. If your early-evening sky is dark enough you will be able to see the winter Milky Way. It runs vertically from Canis Major low in the southeast, up between Orion and Gemini, through Auriga and Perseus overhead, and down through Cassiopeia, Cepheus, and Cygnus to the northwest horizon in the early evening