Meteor Showers, a Supermoon, and the Solstice: A Guide to the December Night Sky

Thomas Coex/AFP/Getty Images
Thomas Coex/AFP/Getty Images

This has been a fantastic year for sky watching. Eclipses in particular had their day in the Sun, with celestial objects blotting each other out as if in competition. There was a penumbral lunar eclipse and an annular solar eclipse in February, and then in August, a partial lunar eclipse was followed up by a mind-blowing total solar eclipse. If you missed any or all of those events, don't lose heart: they will happen again and again and again, in your lifetime and beyond. Celestial mechanics guarantee it. The year isn't over yet, though, and December has a few wonderful events up its sleeve. Here are four things you should be on the lookout for in the skies above.

DECEMBER 3: THE ONLY SUPERMOON OF 2017

I know, supermoons are so 2016. There were six that year, if you don't recall. (I do, because I had to think of new things to write about every single one of them.) This year has been a bit less active in terms of super lunar events, with a total of zero must-see giant moons for your viewing pleasure. That changes on December 3 with the first and only supermoon of the year, and it has a great name at that: the Full Cold Supermoon. The "cold" part of the name, according to the Old Farmers Almanac, derives from Native American tradition. (They weren't being creative here; it's just really cold in December.) The "super" part is because the Moon will be at perigee—that is, the closest to Earth it's going to get in its orbit. The moon's orbit is not a perfect circle, meaning it sometimes appears larger in the sky than others.

Expect a moon that's about 14 percent larger than when it is at apogee (farthest from Earth), though, unless you are an obsessive moonwatcher, the larger size will be nearly imperceptible. My advice is to point at the moon when your friends are around and say something like, “Hey, check that out. I think that's a supermoon! You might not notice a difference, but I sure do. Compared to the moon at apogee, it's huge! Why, it's got to be 14 percent larger, at least. Wow!” Then change the subject quickly, because nobody likes a know-it-all.

DECEMBER 13–14: MORE THAN 100 METEORS PER HOUR

The Geminid meteor shower is considered the best meteor shower of the year, and it peaks after midnight between December 13 and 14. If you are in an area of low (or no) light pollution, and if you give your eyes an hour to adjust to total darkness, and if the weather is good (a lot of "ifs," but worth it if you can arrange things), you can expect to see more than 100 meteors per hour. Geminid meteors are a result of the Earth colliding into the debris field of the asteroid Phaethon, an unusual "rock comet" that leaves behind dust- and sand-sized particles as it circles the Sun. A speck of dust might not seem like much, but when the atmosphere of a 13,170,000,000,000,000,000,000,000-pound planet plows into it at tens of thousands of miles per hour, it is vaporized in a beautiful streak of light.

As if that isn't cool enough, on December 16, Phaethon itself will make its closest approach to Earth in 43 years! Yes, the Minor Planet Center officially considers Phaethon to be a "potentially hazardous object," but before you dust off your Y2K prepper supplies, know that the asteroid will be 27 times farther away than the Moon generally is from the Earth. Sadly, it is unlikely to affect the meteor shower in any measurable way.

DECEMBER 21: THE WINTER SOLSTICE

December 21 will play host to the longest night of the year. Why? Because the Earth's axis is tilted by about 23.5 degrees, and as we orbit the Sun, different latitudes are in direct sunlight. Presently, the southern hemisphere is “closer” to the Sun than the northern. On the 21st, the Tropic of Capricorn (latitude -23.5 degrees) will be in the overhead sun and will receive 13 hours, 27 minutes of daylight. The higher in latitude you go from the Tropic of Capricorn, the less daylight that part of the Earth will receive. The equator will get 12 hours of sunlight. The North Pole will get zero seconds of daylight. The Tropic of Cancer will get about 10.5 hours.

We call this the Winter Solstice, and it's when you'll find some of the best parties of the year. That much night, after all, and anything can happen. Starting on the 22nd, the days will begin to get longer in the northern hemisphere, with spring soon to follow.

DECEMBER 22: THE URSID METEOR SHOWER

Just before sunrise on the morning of December 22, as you're stumbling home from that killer Winter Solstice party, look up. Well, first find a spot with low light pollution and give your eyes time to adjust, and then look up. You will be treated to the annual Ursid meteor shower, here to ring out 2017—and not a minute too soon.

The Ursids are no Geminids; at best you'll only catch 10 meteors an hour, but because the Moon will be but a sliver, the natural skies should be nice and dark. Weather not cooperating? Don't worry. You should be able to catch an Ursid or two through December 25. (Note that on the night of the 24th, what you suspect is an Ursid might be a sleigh carrying cargo and an elderly, bearded man. A distinct red hue will help you distinguish the two. One is a shooting star. The other is Rudolph's nose.)

Friday’s Best Amazon Deals Include Digital Projectors, Ugly Christmas Sweaters, and Speakers

Amazon
Amazon
As a recurring feature, our team combs the web and shares some amazing Amazon deals we’ve turned up. Here’s what caught our eye today, December 4. Mental Floss has affiliate relationships with certain retailers, including Amazon, and may receive a small percentage of any sale. But we only get commission on items you buy and don’t return, so we’re only happy if you’re happy. Good luck deal hunting!

3D Map Shows the Milky Way Galaxy in Unprecedented Detail

ESA
ESA

It's our galactic home, but the Milky Way contains many mysteries scientists are working to unravel. Now, as The Guardian reports, astronomers at the European Space Agency have built a 3D map that provides the most detailed look at our galaxy yet.

The data displayed in the graphic below has been seven years in the making. In 2013, the ESA launched its Gaia observatory from Kourou in French Guiana. Since then, two high-powered telescopes aboard the spacecraft have been sweeping the skies, recording the locations, movements, and changes in brightness of more than a billion stars in the Milky Way and beyond.

Using Gaia's findings, astronomers put together a 3D map that allows scientists to study the galaxy in greater depth than ever before. The data has made it possible to measure the acceleration of the solar system. By comparing the solar system's movement to that of more remote celestial objects, researchers have determined that the solar system is slowly falling toward the center of the galaxy at an acceleration of 7 millimeters per second per year, The Guardian reports. Additionally, the map reveals how matter is distributed throughout the Milky Way. With this information, scientists should be able to get an estimate of the galaxy's mass.

Gaia's observations may also hold clues to the Milky Way's past and future. The data holds remnants of the 10-billion-year-old disc that made up the edge of the star system. By comparing it to the shape of the Milky Way today, astronomers have determined that the disc will continue to expand as new stars are created.

The Gaia observatory was launched with the mission of gathering an updated star census. The previous census was conducted in 1957, and Gaia's new data reaches four times farther and accounts for 100 times more stars.

[h/t The Guardian]