Skywatch Line for Friday, February 23 through Sunday, February 25, 2018

This is Dudley Observatory’s Skywatch Line for Friday, February 23 through Sunday, February 25, written by Sam Salem.

On Friday, Sun rises at 6:41am and sets at 5:38pm; the first quarter Moon occurs at 3:09am and sets at 2:00am on Saturday. See the first quarter Moon shines left or upper left of Aldebaran, and farther upper right of Orion on Friday.

On Saturday evening, the waxing gibbous Moon shines inside the huge pattern of stars known as the Winter Circle. Rigel, Aldebaran, Capella, Procyon, Sirius, Castor and Pollux are the bright stars that make up the large, circular pattern. Orion’s bright red star Betelgeuse resides at the center of the Winter Circle.

On Sunday night, look for the Gemini stars, Castor and Pollux, and the little Dog Star, Procyon. The Moon passes south of Castor and Pollux, and north of Procyon, the brightest star in the constellation Canis Minor, the Little Dog. Look for the Moon and these stars to reach their high point for the night somewhere around 9 to 10pm.

Try to spot Venus for the first time this year. The magnitude –3.9 “evening star” is now setting nearly an hour after the Sun. However, it might be a challenge to see without binoculars unless you have a completely unobstructed horizon to the west. Watch the trio of bright planets arrayed across the southeast sky at dawn. Jupiter, at magnitude –2.1, is located in constellation Libra. Jupiter reaches the meridian around 5:30am, at an altitude less than 30 degrees. Mars, at magnitude 0.9, sits 20 degrees high in the south-southeast and shines a little less than 8 degrees from magnitude 1.1 Antares, in Scorpius. Mars and Antares are closely matched in tint and brightness. Farthest east in Sagittarius is 0.5-magnitude Saturn hovering about 10 degrees above the southeast horizon in early dawn. Draw a line from Jupiter through Mars, extend the line farther on by about the same distance to find Saturn.

Watch sunrise on Mare Imbrium, the Moon’s largest nearside feature. Over the weekend, the terminator sweeps most of the way across the mare’s 1,300-kilometre expanse. Focus on Imbrium’s surface and notice the conspicuous undulations and wrinkles. Find the few large craters near its eastern shore, including Archimedes (82-km diameter), Aristillus (55 km) and Autolycus (39 km).

Supernova 1987A was first seen on February 23, 1987. It was discovered independently by Ian Shelton and Oscar Duhalde at the Las Campanas Observatory in Chile on February 24, 1987, and within the same 24 hours by Albert Jones in New Zealand. SN 1987A was a supernova in the outskirts of the Tarantula Nebula, in the Large Magellanic Cloud, a nearby dwarf galaxy. It occurred approximately 51.4 kiloparsecs (168,000 light year) from Earth. This was close enough to be easily visible to the naked eye and it was seen from the Southern Hemisphere. It was the closest observed supernova since SN 1604, which occurred in the Milky Way.

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