Skywatch Line for Friday, January 20, through Sunday, January 22, 2017

This is Dudley Observatory’s Skywatch Line for Friday, January 20, through Sunday, January 22, written by Sam Salem.

On Friday, the Sun rises at 7:20am and sets at 4:54pm; the 43% illuminated Waning Crescent Moon rises at 12:41am reaching transit altitude of 37 degrees south at 6:19am.

Jupiter is 3.4 degrees north of star Spica on Friday morning. Jupiter rises after midnight. Saturn appears at around 5:30 am, climbing to an altitude of roughly 10 degrees as twilight brightens. Last up is Mercury. It sits roughly four degrees above the southeast horizon one hour before sunrise. Before dawn, try to locate the head of Scorpius, the Scorpion, sticking up above the horizon. Look for the three moderately bright stars that make up the Scorpion’s head to the west of Antares: Graffias, Dschubba and Pi Scorpii. Use the Moon to find Saturn and Graffias before dawn. The northernmost of these three stars, Graffias, serves as a guide to the planet Mercury as darkness begins to give way to dawn. Mercury is actually brighter than either Saturn or Antares. However, Mercury sits lower in the sky quite close to the horizon.

Asteroid Vesta, shining at magnitude 6.2, is now a prime target for binoculars and telescopes. The asteroid was first sighted by Heinrich Wilhelm Matthias Olbers in March 1807. The big rock, measuring roughly 525 kilometers across, makes the second biggest asteroid-belt object, after Ceres. As Ceres has been reclassified as a “dwarf planet”, the title of largest asteroid now belongs to Vesta. Vesta currently resides in easternmost Gemini, about five degrees south-southeast of Gemini’s brightest star, Pollux. This weekend, Vesta is retrograding, drifting westward, toward a four-arc-minute-wide pair of 7th-magnitude stars. On the Friday and Saturday evenings Vesta will be approaching the two stars, and on Sunday night the asteroid will begin to slowly move just north of them. Vesta’s proximity to the double stars will make the asteroid’s motion easy to detect in binoculars or a small telescope.

The famous Andromeda galaxy, the large spiral galaxy next-door to our Milky Way, can be seen with the unaided eye if the sky is dark enough. On a dark night, the Andromeda galaxy looks like a faint, blurry patch of light. From the Great Square of Pegasus look westward for the four stars of the Great Square. You’ll find them high in the west at early evening. The Great Square will sink toward the west-northwest horizon as evening deepens. Look for the constellation Andromeda as two streamers of stars jutting up from this uppermost Great Square star. Go to the second star upward on each streamer, Mirach and Mu Andromedae. Draw an imaginary line from Mirach through Mu, going twice the Mirach/Mu distance. You’ve just located the Andromeda galaxy.

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