Skywatch Line for Friday, January 27, through Sunday, January 29, 2017

This is Dudley Observatory’s Skywatch Line for Friday, January 27, through Sunday, January 29, written by Sam Salem.

On Friday, the Sun rises at 7:15am and sets at 5:03pm; the New Moon occurs at 7:07 pm. The Moon transitions from the morning to the evening sky. As the Sun sets on Saturday, the Moon will be around one-day old. Try to catch the very slender lunar crescent over the western horizon around 30 to 45 minutes after sunset. On Sunday night, look westward after sunset to view the Moon and Venus. The slender waxing crescent Moon will sit rather low in the sky, and will follow the Sun beneath the horizon by early evening. The Moon goes westward toward the sunset each day. Yet, the Moon is moving eastward with respect to the background stars and planets of the zodiac, due to its motion in orbit around Earth. That motion causes the Moon to move eastward 12 degrees eastward per day, with respect to the Sun. Which is about 13 degrees eastward per day as measured by the backdrop stars.

In this moonless weekend look for the sky’s brightest star, Sirius, and the faint star cluster near it. The three prominent Belt stars in the constellation Orion point to Sirius. That fuzzy spot near Sirius is a star cluster called Messier 41. This cluster lies about four degrees south of Sirius. M41 is sometimes also called the Little Beehive, after the other famous Beehive star cluster (M44), also an open cluster, in the constellation Cancer. In the late 1700s, Charles Messier gave this object the number 41 on his list of “objects to avoid.” He was a comet hunter who wanted others to realize that this object, which looks like a comet. The cluster contains about 100 stars including several red giants. Like most open star clusters of this type, it is relatively young, probably between 190 and 240 million years old.

The Sword of Orion, there you’ll find an open cluster, a double star, and one of the most magnificent nebulas in the entire sky. All three targets can be observed with a small telescope, or binoculars. The Orion Nebula (M42) is located just to one side of the line between Rigel and Alnilam, the middle star in the Orion Belt. The Nebula is a faint, fuzzy blue patch in the Sword of Orion, an asterism composed of Iota Orionis, the Orion Nebula, and NGC 1981. North of M42, at the top of the Sword, sits the open cluster NGC1981. It’s a group of modestly bright stars occupying a patch of sky roughly half a degree in diameter. Next, a little south of the Orion Nebula is Iota Orionis. Iota is a binary star, but its tight, 7th-magnitude companion is difficult to detect in low-power optics. However, just 8 arc minutes south of Iota, at the very bottom of the Sword, is a widely spaced double star, Struve 747, that can be easily split in a small scope.

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