Skywatch Line for Friday, February 9 through Sunday, February 11, 2018

This is Dudley Observatory’s Skywatch Line for Friday, February 9 through Sunday, February 11, written by Sam Salem.

On Friday, Sun rises at 7:01am and sets at 5:19pm; the Waning Crescent Moon rises at 2:16am and sets at 12:19pm. On Friday, The Moon meets up with Mars at dawn and sits roughly four degrees east-northeast of the red planet. The Moon continues its eastward journey along the ecliptic. On Sunday morning, the lunar crescent is less than two degrees north of Saturn. The two are low in the southeast at dawn.

Jupiter, at magnitude –2.0, becomes visible around 1:30am. Jupiter climbs to the meridian a little before 6:30am. Mars shines at magnitude 1.1 at the southeast horizon around 3am. Mars and Antares, the brightest star in the constellation Scorpius, are at their closest Sunday and Monday mornings. They are separated by approximately five degrees. Saturn, at magnitude 0.6, rises roughly 2½ hours ahead of the Sun. Saturn, the most distant of the bright planets, takes nearly 30 years to travel full circle in front of the constellations of the zodiac. Jupiter, which is farther than Mars but closer than Saturn, completes the trip through the zodiac in nearly 12 years. Mars, just one step outward from Earth, takes a little less than two years to complete one trip in front of the backdrop stars. Because Mars goes so much faster than either Jupiter or Saturn, Mars routinely laps Jupiter and Saturn in Earth’s sky. Mars recently lapped Jupiter on January 7 this year. It will lap Jupiter again on March 20, 2020. These Mars/Jupiter conjunctions recur in periods of a little over two years.

The region known as the Sword of Orion is one of the season’s treasures. There you find an open cluster, a fine double star and one of the most magnificent nebulas in the entire sky. The Orion Nebula (M42) is bright enough to be visible even in light-polluted conditions. M42’s luminous core is pricked by four tightly-spaced glints known as the Trapezium. North of M42, at the top of the Sword, sits the open cluster NGC1981. It’s an attractive smattering of modestly bright stars occupying a patch of sky roughly half a degree in diameter. Next, look a little south of the Orion Nebula for 2.8-magnitude Iota (ι) 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 can’t-miss double called Struve 747. All targets can be appreciated with the smallest of telescopes, or even binoculars.

On February 11, 1801, Giuseppe Piazzi made his 24th observation of the position of Ceres, the asteroid he discovered earlier that year between the orbits of Mars and Jupiter. After this observation, Ceres moved into the light of the Sun, and was lost to view for most of the rest of the year. Carl Gauss, at age of 24, took up the challenge to mathematically relocate Ceres by calculating its orbital path based on the limited number of observations available. His method was tedious, requiring 100 hours of calculation. He began with a rough approximation for the unknown orbit, and then used it to produce a refinement, which became the subject of another improvement. Astronomers found Gauss’ results in close agreement as they located Ceres again in November 25- December 31 1801.


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