December marks the beginning of winter in the northern hemisphere. The season will turn at exactly 11:19 p.m. on Dec. 21. It will also be our longest night and shortest day of the year, aka the winter solstice, when the sun reaches its lowest point in our sky for the year. Immediately after, the days begin to lengthen again, though slowly. We will not notice for several more weeks.
It’s well worth braving colder temperatures to see the many interesting highlights this month. They include a nice conjunction of Venus and Saturn in the evening sky; Mercury and Mars in the morning sky; nice conjunctions of Venus and the moon in the evening sky and Mars and the moon in the morning sky; a comet named PanStarrs; an annular solar eclipse visible over parts of Africa, Asia, and the western Pacific; and not one, but two meteor showers, the Ursids and the Geminid Meteor shower, which is usually the best shower of the whole year.
Late last month, Venus caught up with and then passed Jupiter. Now you can watch the much faster-moving, brighter Venus catch up with and then pass Saturn in the evening sky. Three planets – Jupiter, Venus, and Saturn – will look about evenly spaced on the second and third of this month. Keep watching as Venus will pass within just 2 degrees of Saturn, or four times the width of the full moon, on the Dec. 10-11.
At minus 3.9 magnitude, Venus is about 75 times brighter than Saturn at plus 0.6 magnitude. Every evening, Venus just keeps getting higher, as Saturn keeps sinking lower into the twilight. By the end of this month, we will lose the ringed planet completely. Remember that we just discovered 20 new moons around Saturn, bringing its total to 82 (for now), the most of any planet in our solar system.
As you could see on any good app depicting the sky on your phone, Venus, Saturn, and Pluto will fit together in a circle just 2.5 degrees in diameter on Dec. 12. They are clustered together now in eastern Sagittarius in an asterism called the teaspoon, which goes with the larger asterism of Sagittarius known as the teapot. You would need a good amateur telescope to see Pluto – an amazing icy dwarf planet with an atmosphere, ice volcanoes, and many other unique features – since it is 18 magnitudes, or about 13 million times fainter than Venus.
Mercury and Mars are in the morning sky. Mercury made a steep climb into the morning sky after its great transit last month on Veterans Day. By the middle of this month, our first planet will be lost to our view. Mars is ever so slowly getting higher and brighter and closer to Earth. We are catching up with the red planet, but it will not reach opposition until Oct. 13, 2020.
Comet PanStarrs will be visible in Perseus the Hero all month long. It should reach 9th or 10th magnitude, so you would need a small telescope to see it. This comet is still getting closer to the sun and Earth and is expected to reach 7th magnitude by May of next year.
We are in an eclipse season once again, though we won’t see any total eclipses of the sun or the moon. The last eclipse season, in July of this year, featured a partial lunar eclipse on July 16, coincidentally the 50th anniversary of the launch of Apollo 11, which landed the first human on the moon. July 2 offered a total solar eclipse over Chile and Argentina, the first total solar eclipse anywhere on Earth since the Great American Total Solar Eclipse on Aug. 21, 2017.
This month, we will only have an annular solar eclipse on Dec. 26 at new moon, and it will only cross over parts of Africa, most of Asia, and parts of the western Pacific. Annular, by the way, means ring-shaped (not yearly). Since the moon will be close to apogee, or farthest from the sun, it will not quite be able to cover the entire sun during this eclipse, resulting in a brilliant ring of fire glowing around the sun. Twenty-five years ago, on May 10, 1994, I saw one of these right here in Maine. Though a very interesting event, it was nothing like a total solar eclipse. The difference is – literally – like night and day. With 97 percent of the sun covered by the moon during an annular eclipse, it will still basically look like daytime, except that the atmosphere will take on a silvery glow and the temperature will drop a few degrees.
During a total solar eclipse, the whole sky gets dark, but not pitch black. The planets and brighter stars instantly become visible and the corona, or atmosphere, of the sun extending many times the diameter of the sun dominates the sky with a shimmering ethereal glow. This corona is always there, but only visible when the rest of the sun is completely covered by the moon.
The Ursid meteor shower will peak on Dec. 23, close to new moon. Caused by Comet 8P/Tuttle, which orbits the sun every 14 years, this shower will produce only about 10 meteors per hour. An outburst is always possible, though, and forecasters have predicted a minor outburst this year that could triple its rate. Keep in mind that the predicted outburst of the Alpha Monocerotids late last month never materialized.
The Geminid meteor shower will peak on the morning of Friday, Dec. 13. The moon will be just past full, so will rise about one hour after sunset, washing out much of the show. However, if you can look the other direction in the sky from the moon, you could still see quite a few meteors. That’s because the Geminids – caused by a hybrid of a comet and an asteroid called 3200 Phaethon – tend to be much brighter than other meteors.
DECEMBER HIGHLIGHTS
Dec. 1: A string of three planets and the waxing crescent moon are visible in the evening sky.
Dec. 4: First quarter moon is at 1:58 a.m.
Dec. 7: Gerard Kuiper was born on this day in 1905. The Kuiper belt of trillions of small objects, including Pluto, is named after him.
Dec. 10: Venus and Saturn are less than 2 degrees apart, low in the western evening sky.
Dec. 11: Annie Jump Cannon was born on this day in 1863 in Delaware. Along with several other famous women astronomers who became known as the “Harvard Computers,” she helped develop the stellar classification system.
Dec. 12: Full moon is at 12:12 a.m. This is also known as the Cold, Long Night, or Moon before Yule.
Dec. 13: The Geminid Meteor shower peaks this morning.
Dec. 14: Tycho Brahe was born on this day in 1546. Born before telescopes were invented, he was the best observer of his day. Brahe’s careful observations of Mars helped Kepler develop the three laws of planetary motion.
Dec. 17: The first powered flight occurred on this day in 1903. Fewer than 66 years later, we would fly humans to the moon.
Dec. 18: Last quarter moon is at 11:57 p.m.
Dec. 21: The winter solstice is at 11:19 p.m.
Dec. 22: The Ursid Meteor shower peaks today. An outburst is expected this year.
Dec. 23: The waning crescent moon passes near Mars in the morning sky.
Dec. 25: Isaac Newton was born on this day in 1642.
Dec. 26: New moon is at 12:13 a.m. An annular solar eclipse occurs today.
Dec. 27: Johannes Kepler was born on this day in 1571. The moon is within 1 degree of Saturn.
Dec. 28: The moon and Venus will be 1 degree apart this evening. English astronomer Sir Arthur Eddington was born on this day in 1882.
Bernie Reim of Wells is co-director of the Astronomical Society of Northern New England.
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