Skywatch Line for Friday, December 7 through Sunday, December 9, 2018

This is Dudley Observatory’s Skywatch Line for Friday, December 7 through Sunday, December 9, written by Sam Salem.

On Friday, the Sun rises at 7:13am and sets at 4:22pm. Every year, toward the end of the first week of December, mid-temperate latitudes in the Northern Hemisphere have their earliest sunsets. For our area, the earliest sunset takes place from December 2nd till December 15th when the Sun sets at 4:22pm. This comes a few days before December solstice. This offset from the solstice date is balanced out by the opposite happening at sunrise as the Sun doesn’t come up its latest until January 2nd.. This offset is caused by the tilt of Earth’s axis and the eccentricity of Earth’s orbit.

On Friday, the new Moon occurs at 2:20am, it rises at 7:16am and sets at 4:58pm, which is very close the sunrise and sunset time. On Saturday, the very young Moon and Saturn pair up very low in the southwest at dusk. Both objects can be seen together in binoculars. Saturn is 1.1 degrees south of the Moon on Sunday. To enjoy this conjunction, you’ll need a location with an unobstructed horizon. Pluto is 0.7 degrees south of the Moon on Sunday night. Use the new Moon to guide you to the dwarf planet Pluto.

Saturn, shining at magnitude 0.5, is nearing the end of its current apparition and sets at the end of twilight, at roughly 6:00pm. Mars, at zero-magnitude, transits the meridian at about the same time Saturn is setting. Mars can still offer patient observers some interesting telescopic views. Mars sets around 11:30pm. Mars is 0.04 degrees north of Neptune on Friday.

Venus dominates the dawn sky. Gleaming at its very brightest, at magnitude –4.9, Venus is impossible to miss as it rises in full darkness around 3:35am. Joining Venus for a brief morning appearance is Mercury at magnitude 0.6. The swift little planet rises approximately one hour ahead of the Sun.

This weekend provides a good opportunity to catch a glimpse of Comet 46P/Wirtanen. The icy visitor is inbound and cruising north through Eridanus toward Taurus. Currently glowing at approximately magnitude 6, the comet won’t be at its brightest until its closest approach with Earth next weekend. However, 46P should be readily visible in binoculars used under a sky free from light pollution. Comet Wirtanen spends the weekend roughly 7 degrees south-southeast of 2.5-magnitude Alpha (α) Ceti, the brightest star in the region. The comet is visible most of the night, but is highest shortly after 10pm.

Friday marks the 113th. birthday of the Dutch-American Astronomer Gerard Kuiper. Kuiper is considered by many to be the father of modern planetary science. He discovered Uranus’s satellite Miranda and Neptune’s satellite Nereid. In addition, he discovered carbon dioxide in the atmosphere of Mars and the existence of a methane-laced atmosphere above Saturn’s satellite Titan in 1944. Kuiper discovered several binary stars which received “Kuiper numbers” to identify them, such as KUI 79. Astronomers refer to a region of minor planets beyond Neptune as the “Kuiper belt”, since Kuiper had suggested that such small planets or comets may have formed there. However he believed that such objects would have been swept clear by planetary gravitational perturbations so that none or few would exist there today.

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