This is Dudley Observatory’s Skywatch Line for Friday, August 23 through Sunday, August 25, written by Sam Salem.
On Friday, Sun rises at 6:10am and sets at 7:46pm; the last quarter Moon sets at 1:56pm. On Friday, the Moon reaches last-quarter phase at 10:56am. On Saturday, soon after the Moon rises in the early morning hours, watch it slowly drift through the Hyades cluster in constellation Taurus. The sooner you look the closer the Moon will be to the cluster stars. The conjunction will be a fine binocular sight.
It’s summer in the northern hemisphere; however, a major sign of winter now looms large in the predawn sky. The waning crescent Moon shines right in front of the Winter Circle on Sunday and Monday mornings. The Winter Circle, or the Winter Hexagon, is an asterism, a star pattern that is not a recognized constellation. This star formation consists of six 1st-magnitude stars in six different constellations; Capella of the constellation Auriga the charioteer, Pollux of the constellation Gemini the Twins, Procyon of the constellation Canis Minor the Smaller Dog, Sirius of the constellation Canis Major the Big Dog, Rigel of the constellation Orion the Hunter, and Aldebaran in the constellation Taurus the Bull.
Jupiter and Saturn are both well placed as twilight fades. Jupiter, gleaming at magnitude –2.3, is the first star-like dot you notice at dusk. The giant planet now culminates around sunset. The earlier you train your scope and your eyes on Jupiter, the better you will be able to inspect its cloud belts, Great Red Spot and the four Galilean moons. Jupiter sets around 12:15am. Saturn, shining at magnitude 0.3 from eastern Sagittarius, isn’t at its best until slightly around 10:00pm. Saturn rings are tilted open at nearly the maximum angle possible, making it an easy target in any telescope. Saturn sets around 2:30am. Mercury is the solitary dawn planet and it’s a bit of a challenge to view. Mercury, glowing at magnitude –1.2, is reaching the end of a favorable morning apparition. It rises a little more than one hour ahead of the Sun. An unobstructed east-northeast horizon will be a big help when it comes to spotting Mercury.
Check out some dark nebulas these moonlight-free weekend evenings. Find a location free from significant light pollution. Look along the band of the Milky Way. You’ll notice numerous dark rifts and patches. One conspicuous area, known as the Northern Coal Sack, hides in the southeast of the 1.2-magnitude Deneb, the brightest star in Cygnus. This feature is part of a much larger dark assemblage known as the Great Rift, which bisects the summer Milky Way for much of its length. You don’t need a telescope to spot the Northern Coal Sack. You just need a dark sky. The Northern Coal Sack is so big that even binoculars diminish its appearance. Another well-known dark nebula is Barnard’s E, located a few degrees northwest of 0.9-magnitude Altair, the brightest star in Aquila. Use binoculars or a small, wide-field telescope, and look for a ragged, E-shaped blackish blob, about one degree due west of 2.7-magnitude Gamma (γ) Aquilae. Observing the ghostly E takes some effort. But once you train your eye to look for an absence of starlight, you’ll be surprised at the number of other dark nebulas you can pick up with binoculars.