This is the Griffith Observatory Sky Report through January 2, 2019. Here’s what’s happening in the skies of southern California.
Winter begins in the northern hemisphere at 2:23 p.m., PST on December 21st. This is the December Solstice, and it marks the time that the north side of earth’s rotation axis is tilted by its maximum amount–23½ degrees–away from the sun. As a consequence, the sun appears at its farthest south in the sky for the year, which gives the northern hemisphere it’s shortest day and longest night. At Los Angeles, the sun is visible for 9 hours and 53 minutes. In the southern hemisphere, the same solstice marks the start of summer and is the southern hemisphere’s longest day and shortest night. The season will end with the equinox on March 20.
A normally inconspicuous comet, that orbits the sun every 5.4 years–46P/Wirtanen, will make an unusually close approach to Earth on the night of December 15, when it will come within 7.3 million miles. This has made it visible to the unaided eye from wilderness locations free from light pollution, but it is difficult or impossible to see from most suburban or urban locations where the sky is brightened by the presence of artificial light. From a dark sky–the kind of sky across which the Milky Way is easily visible–the comet is impressive. The comet appears as a luminous round cloud, more than twice as wide as the apparent size of the full moon, and binoculars will aid in seeing it. It is also very photogenic, and it shows a distinctive green color that is easy to record in time exposures that can be made with a DSLR camera mounted on a tripod, or even with a smartphone using camera control apps. The comet is visible all night long, and is moving northeastward. It is in the constellation Taurus the Bull through December 17, appears in the southeast corner of Perseus the Hero through the 20th, and moves across Auriga the Charioteer before moving into moving into Lynx the Lynx on December 28th. The comet is highest in the sky at about 10:00 p.m., but the best time to see it will be determined by when the moon is not in the sky. Before the 21st, the best time is a shrinking interval between moonset and 5:25 a.m., the start of dawn. The time of moonset can be found on Griffith Observatory’s website. The full moon on the 22nd is too close to the comet to avoid moonlight starting on the 21st. Beginning on December 24th, the best time to see the comet will be in the increasingly long interval between 6:20 p.m., when the sky becomes dark, and moonrise, also found on the Griffith Observatory website.
The year’s strongest meteor shower, the Geminids, reaches its peak on the night of the 13th though dawn of the 14th. From a dark sky, up to 120 Geminid meteors may be seen per hour at 2:00 a.m., when the constellation Gemini, from which the meteors appear to stream, is overhead. Observing conditions are best after the moon sets at 10:37 p.m.
The planet Mars moves from the backdrop of stars in the constellation Aquarius the Water Bearer to that of Pisces the Fishes on December 21st. It appears starlike and orange, and is located high in the south-southwest sky when darkness falls, and it sets at about 11:00 p.m. The waxing crescent moon appears near Mars on December 12.
Venus, the brightest planet, is eye catching in the southeastern sky before dawn. Fainter planet Mercury appears close to the horizon, to the lower left of Venus throughout December, and by the end of the month, Jupiter will also appear near Mercury. The slender waning crescent moon poses near Venus on January 1st.
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 15.
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From Griffith Observatory, I’m Anthony Cook, and I can be reached at griffithobserver@gmail.com.