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The Sky This Week, 2021 December 7 - 14

Seasonal lights in the sky
Jupiter with Ganymede in transit, 2021 November 30, imaged from the U.S. Naval Observatory, Washington, DC
Jupiter with Ganymede in transit, 2021 November 30
imaged from the U.S. Naval Observatory, Washington, DC
with the 30.5-cm (12-inch) f/15 Clark/Saegmüller refractor
and a ZWO Optical ASI183MC CMOS color imager.

The Moon waxes in the evening sky this week, passing the gas giant planets as the week begins, then climbing toward the rising winter stars through the week’s end.  First Quarter occurs on the 10th at 8:36 pm Eastern Standard Time.  Look for Luna’s crescent to the southwest of Saturn on the evening of the 7th.  On the following night she forms a triangle with Saturn and bright Jupiter. 

This is the week when residents of northern temperate latitudes experience the earliest sunsets of the year.  Here in Washington sunset occurs at 4:46 pm EST for the evenings up to the 11th.  By the 14th sunset will occur about a minute later.  In the meantime the times of sunrise continue to occur later each morning and will continue to do so through the end of the year.  By the start of the new year sunrise will be some 13 minutes later than it is on the 7th.  Between the time of latest sunrise and earliest sunset is the winter solstice, which will mark the shortest day of the year in the Northern Hemisphere.

The night of the 13th and 14th marks the peak of the annual Geminid meteor shower.  Over the past several years this shower has become the most consistent meteor display of all the annual showers, with hourly rates of 60 to 80 or more meteors visible to a single observer under dark skies.  It is also one of the only major meteor showers to display good activity before midnight.  The radiant point is near the bright star Castor in the constellation of Gemini and rises early in the evening.  By late evening it is high in the eastern sky.  This year’s shower is partly obscured by the bright light of the 11 day-old Moon, but after 2:00 am Luna’s glare will have subsided and Gemini is high overhead.  The stream of particles that produces the Geminids originates from one of the solar system’s strangest objects, an asteroid known as 3200 Phaethon.  This was the first asteroid to be discovered by a satellite observatory, the Infrared Astronomical Satellite, which spotted it in 1983.  Phaethon is a member of the Apollo family of asteroids that have perihelia inside the orbit of the Earth.  Its orbit is quite eccentric and resembles those of periodic comets, which may belie its origin.  It passes closer to the Sun than any currently known named asteroid.

Gemini sits at the top of a large asterism that is now brightening the eastern sky.  Known as the “Great Winter Circle”, it comprises of several of the brightest and most colorful stars in the sky.  By 10:00 pm local time the Circle dominates the eastern sky surrounding the distinctive constellation of Orion, the Hunter.  Starting with Rigel, the bright blue “foot” of the Hunter, a counter-clockwise loop around the sky will bring your gaze to reddish Aldebaran in Tauris, golden Capella in Auriga, the Gemini Twins Castor and Pollux, whitish Procyon in Canis Minor, and finally the dazzling blue brilliance of Sirius, the brightest star in the heavens.  Within the bounds of the Circle you will find nine of the 25 brightest stars in the sky, a bright and colorful display in the sky that rivals any human-made light seasonal light show here on Earth.

Venus leads a lineup of bright planets in the early evening hours.  The dazzling planet is currently shining at her brightest for the year, and is easily seen in the southwest at sunset.  Catch her while you can, since she begins a precipitous plunge toward the Sun that will cause her to vanish into the Sun’s glare early in January.

Saturn may be found almost exactly halfway between his bright companions Jupiter and Venus.  He receives a visit from the Moon on the evenings of the 7th and 8th.  His time in the sky is also limited, and by the end of the year he, too, will become harder to find after twilight’s end. 

Jupiter brings up the rear of the planetary parade and can be seen high in the southwest as twilight gathers.  Old Jove is still a good target for the telescope in the early evening hours, but you need to hurry.  His bright glimmer sets by 10:00 pm.