The chart above shows the hours of daylight during the year (the red line). The blue shaded area shows the daylight hours during December. (Calculated from data from the U.S. Naval Observatory.)
December, the month of the shortest daylight hours, is upon us. The day with the longest daylight is December 1 with 9 hours, 22 minutes in the Chicago area. The daylight hours decrease (9 hours, eight minutes) until the winter solstice. The sun reaches is farthest south point on December 21 at 5:03 p.m. CST. At this time the sun is overhead from 23 degrees south of the equator in the Pacific Ocean, at the Tropic of Capricorn. By month’s end the daylight hours begin to lengthen (9 hours, 11 minutes) as the sun appears farther north during our planet’s annual journey around the sun. We have lost 6 hours, 5 minutes of daylight since the summer solstice in June, the peak on the graph above. (Click the images to see them larger.)
||12/06/14 (6:27 a.m.)
||7:47 a.m. (12/07)
||12/14/14 (6:51 a.m.)
||11:27 p.m. (12/13)
||12/21/14 (7:36 p.m.)
||12/28/14 (12:31 p.m.)
||12:30 a.m. (12/29)
|Times are Central Standard Time for Chicago, Illinois, from US Naval Observatory calculations. (For mjb)
Jupiter is the bright “star” low in the east-northeast near midnight as the year’s final month opens. It is about 7.5 degrees to the upper right of Regulus, the brightest star in the constellation Leo. At this hour, the head of the lion appears to the left of Jupiter. Known to sky watchers as the “Sickle,” the star pattern resembles a backwards question, although it is named for the cutting tool used in agriculture.
By 5 a.m. Jupiter and Regulus are high in the southern sky. On about August 22 each year, the sun appears to pass about 1/3 degree below Regulus. Because the solar system is largely a plane, like that of a pancake and the bright planets move near the plane, the sun, moon and bright planets regularly appear near Regulus. Regulus, along with several other stars, are signposts of the solar system.
On December 12, the moon clusters with Jupiter and Regulus. As explained above, this trio appears high in the south before sunrise. On this evening, Jupiter is about 7.5 degrees to the upper right of Regulus and 6 degrees to the upper left of the moon.
By month’s end Jupiter rises in the eastern sky around 8 p.m. and shines in the sky during the rest of the night.
Venus begins its evening apparition (appearance) this month. On December 1, it sets only 30 minutes after sunset and remains hidden in the sun’s glare.
The brilliant planet appears low in the southwest during bright evening twilight at mid-month. Depending on the clarity of the sky and the horizon, the first observation of Venus depends on local circumstances at mid-northern latitudes. Venus and separated by about 30.5 degrees on the chart above which is about 35 minutes after sunset.
The moon appears above (11 degrees) Venus on December 23rd during twilight.
On the next evening, as shown on the chart above, the moon appears 6 degrees to the right of Mars. Venus and Mars are about 28 degrees apart. The planets continue to appear closer together in the western sky as the new year opens. They appear closest in late February 2015.
Mercury joins Mars and Venus in the western sky late in the month. On December 31, Mercury is 3 degrees to the lower right of Venus and Mars is 24 degrees to the upper left of Venus.
For more about Venus’ evening apparition, see this article.
With Jupiter rising later in the evening, it rises higher in the sky each hour. Early in the month, it appears in the southern sky near sunrise. As the month progresses, it appears farther west. By month’s end, it appears high in the southwest near sunrise.
Saturn emerges from behind the sun and into the morning sky during the month. It rises in the southeastern sky just before sunrise. On December 19, it appears with the waning crescent moon as depicted in the chart above.
By month’s end, all five naked eye planets (Mercury, Venus, Earth, Mars, Jupiter, and Saturn) are visible during the night. Bundle up, get outside the see Venus emerge from the sun’s glare in the evening sky and see Saturn emerge from the sun’s glare in the morning sky.