This is the Dudley Observatory Skywatch Line for Wednesday, December 4th, and Thursday, December 5th, written by Louis Suarato.
The Moon reaches its First Quarter phase at 1:58 a.m., Wednesday. Moonrise occurs at 1 p.m., and moonset is 14 minutes past midnight as a 65% illuminated, waxing gibbous Moon. Lunar apogee, when the Moon is farthest from Earth during this cycle, occurs at 11:08 p.m., Wednesday, when it will be 251,311 miles away. Saturn, Venus, and Jupiter span above the southwestern horizon at evening twilight. Jupiter will be the first to set at 5:33 p.m., followed by Venus at 6:14 p.m., and Saturn at 6:56 p.m.. Although the fewest total of daylight hours occurs on December 21st during the Winter Solstice, the earliest sunsets of the year take place between December 4th to the 14th, when the sun sets at 4:21 p.m. each day. Meanwhile, sunrises occur later, shortening the total amount of daylight. Look above the east-southeastern horizon for Mars, which rises at 4:24 a.m., and Mercury about an hour later. December 4th is the anniversary of the launching of the Mars rover, Sojourner, along with Mars Pathfinder, aboard a Delta rocket. Launched in 1996, Pathfinder and Sojourner reached the Martian atmosphere on July 4, 1997.
For a preview of the winter sky, look over the east-southeastern horizon after 8 p.m. to see the constellation Orion leaning back toward the Gemini twins. Orion contains two of the top ten brightest stars over our region. Rigel, at the foot of Orion, is the seventh brightest star, shining at magnitude 0.18. This blue supergiant star is a multiple star system estimated to be about 860 light-years away. Betelgeuse, located at Orion’s right shoulder, is a red supergiant star. This variable star is usually the ninth brightest star, but occasionally outshines Rigel, varying between magnitude 0.0 and 1.3, the widest variation of any first magnitude star. Orion is also the home of M42, the Great Orion Nebula. Located below Orion’s Belt, M42 is visible with the naked eye, even under some light-polluted conditions. A telescopic view of the Great Orion Nebula will reveal the Trapezium, a tight open cluster of stars. Discovered by Galileo in 1617, who sketched three stars, six stars of the Trapezium can be resolved with a five inch aperture or higher.