The Griffith Observatory Sky Report
I’m David Nakamoto, and I shall be taking over the monthly Sky Report from Anthony Cook, who is retiring from Griffith Observatory after 42 years.
This is the Griffith Observatory Sky Report through the period ending December 31st, 2020. Here’s what’s happening in the skies of southern California.
The winter solstice is on December 21st at 2:02 a.m. PST. This is when the Sun arrives at its lowest point on its journey along the ecliptic, so it swings through the sky as far south as it can get, as seen by observers in the northern hemisphere. This also marks the shortest day of the year. After the 21st, the days will get longer as the months go by.
The giant planets Jupiter and Saturn are in the southwest. On the 1st, they start off about 25 degrees above the south-southwest horizon and set in the west-southwest by 8:00 p.m. On the 31st, they are 15 degrees above the southwest horizon after sunset and set around 6:30 p.m. Jupiter is the brightest of the pair. Saturn appears about two degrees up and to the left of Jupiter on the 1st. During the month, Jupiter moves slowly east, until on the 31st, Saturn is one degree below and to the right of Jupiter. On the 16th, the Moon is a thin two-day-old crescent five degrees away, down and to the center-left of the pair. On the 17th, it switches to the left of the pair and 11 degrees away.
On the evening of December 21st, the separation between Jupiter and Saturn reduces to one-tenth of a degree, one-fifth the width of the full moon. They have not been this close since 1623! A telescope will show a wonderful sight, with details on both planets visible with suitable magnification. This is the only evening when they’ll be this close. The Moon can’t help in locating them; it’s too far to the east.
Copper-red Mars is receding from us and appears high in the east-southeast after sunset. Mars reaches the meridian at 8:11 p.m. on the 1st and at 6:52 p.m. on the 30th. Mars sets earlier each night, from 2:34 a.m. at the beginning of this period to 1:27 a.m. at the end. The planet remains an excellent target for telescopic observation, but it shrinks from 14 arcseconds on the 1st to 11 arcseconds on the 31st. On the 25th, the gibbous Moon passes below Mars.
The brightest planet, Venus, appears in the morning, low in the east. It rises at 4:27 a.m. on the 1st with the Sun rising at 6:41 a.m. By the 31st, Venus will rise at 5:29 a.m. with the Sun following at 6:59 a.m. A telescope may reveal its current gibbous phase. In the weeks to come, it will appear progressively more full. Venus is on the far side of its orbit as seen from the Earth and will get farther away each week. Its apparent motion gets slower as it continues to move farther from the Earth.
Mercury is too close to the Sun to be observed this month.
The last quarter Moon occurs on the 7th. The Moon is new on the 14th. First quarter is on the 21st, and full moon is on the 30th.
The Geminid meteor shower lasts from December 4th to the 17th, but the peak occurs on the night of the 13th through the morning of the 14th. Geminids are slower and brighter as a whole than most meteors. At the shower’s peak you may see 50 meteors an hour, although some predictions put the peak rate much higher, a 100 per hour or more. Like all meteor showers, the Geminids are named after the constellation from which they appear to be streaking, in this case, Gemini the Twins. Gemini rises at sunset, sets at sunrise, and passes directly overhead at midnight on the 13th/14th, and so it’s an all-night show. Your best viewing requires traveling away from all lights and resting in a low-back lounge chair so your head and neck are aligned with your body, supported by the chair, with your head looking up. Neither binoculars nor a telescope is needed. Dress warmly and prepare for a very cold night. This is winter, and no matter how warm the daylight temperatures may be, at night it gets very chilly.
Measures intended to reduce the spread of the COVID-19 coronavirus keep Griffith Observatory closed to the public until further notice. Please check the Griffith Observatory homepage for current information.