This is the Griffith Observatory Sky Report through December 20, 2017. Here’s what’s happening in the skies of southern California.
The strange object that creates the Geminid meteors is an asteroid called 3200 Phaethon. This is thought to be an asteroid that is rotating so rapidly that its outer layers disintegrate when it passes close to the sun. The particles, called meteoroids, become meteors when they encounter our atmosphere and are vaporized by friction. Because the debris coming off the asteroid resembles the dusty tail of a comet, this kind of asteroid is called a “rock comet.” Phaethon has a highly elliptical orbit that carries it beyond the orbit of Mars to near the sun’s surface and back, every 1.4 years. This year, Phaethon will pass only 6.4 million miles from Earth on the night of December 17, and its brightness will be close to magnitude 11 – bright enough to see through telescopes of six inch or greater aperture – between December 13 and 17. A detailed discussion of observing Phaethon, complete with detailed maps to hunt it down as it speeds through the constellations Perseus and Andromeda, can be found on the Sky and Telescope website. This year’s passage is the closest that Phaethon will come to Earth until 2093.
The moon is waning crescent in the early morning sky through the 16th. It is new on the 17th, and reappears, waxing crescent, above the southwest horizon on the evening of the 19th.
The planets Mars and Jupiter, as well as the star Spica of the constellation Virgo the Maiden, form a line of three bright objects above the southeast horizon as dawn starts. Jupiter is the brightest and the lowest of the three. Orange Mars is to the upper right of Jupiter, and blue-white Spica is to the upper right of Mars. The slender moon poses next to Jupiter on the 14th.
The International Space Station will be the brightest object in the sky as it passes high over Los Angeles on Friday and Saturday nights, December 15th and 16th. Friday’s flyover will take place between 6:15 and 6:20 p.m. as the brilliant satellite moves from the northwest horizon to its high point, 71 degrees high in the southwest at 6:18 p.m., two minutes before it vanishes into the Earth’s shadow, 38 degrees above the south-southeast horizon. On Saturday night, the ISS will cross the sky from the northwestern to the east-southeastern horizons between 5:23 and 5:29 p.m., and it will be at its highest, 51 degrees high in the northeast, at 5:26 p.m.
Free views of the Sun during the day and of the moon, planets, and other celestial objects at night are available to the public in clear weather through Griffith Observatory’s telescopes from Tuesday through Sunday, before 9:30 p.m. Check our website for the schedule. The next free public star party on the grounds of Griffith Observatory, hosted by the Los Angeles Astronomical Society, the Sidewalk Astronomers, and the Planetary Society, will take place on Saturday, December 16th, from 2:00 p.m. until 9:30 p.m.
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From Griffith Observatory, I’m Anthony Cook, and I can be reached at email@example.com.