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Look Up Again! The Final Supermoon of 2016 Rises Tonight

Last month's supermoon: on November 14, you could see it rising above Athens through the propylaea of the Acropolis. Image Credit: AFP/Aris Messinis/Getty Images

 
You might be sick to death of hearing about "supermoons." If that's the case, I bring good news: tonight, December 13, you'll see the final supermoon of 2016. If you're not sick of them, I also bring good news, because you have one more supermoon to see.

Of course, where there is good news there is bad, and it's this: The supermoon will make it very difficult to catch the Geminid meteor shower, which peaks tonight. Don't give up, however; because of the sheer volume of meteors that comprise the Geminids, you might see some shooting across the sky.

WHAT IS A SUPERMOON?

Before last year, when the red harvest supermoon took over the world, you might never have heard of a supermoon. And now we've had three in a row to close out the year: October's super hunter's moon, November's super beaver moon, and now December's full cold or long nights supermoon. This is true in part because supermoon is not an astronomy term, but rather, one of astrology. (In case you are wondering about the difference: astronomy is science; astrology is make believe.) The name has stuck of late because it's Twitter-friendly and a lot easier to remember than the actual name for the phenomenon: perigee-syzygy of the Earth–Moon–Sun system.

If you want to understand what's going on and why there are so many supermoons recently, you really do need to look at the proper name. Perigee occurs when the Moon is closest to the Earth in an orbit. Remember: the Moon's orbit is not a perfect circle; rather, it's elliptical. Sometimes it's close to Earth. Sometimes it's farther away.

Syzygy means three celestial objects are in alignment. (It can be the Sun, Earth, and Moon, but it might be the Sun, Venus, and Earth, for example, when astronomers can view Venus cross the solar disc.) So when do the Earth, Sun, and Moon experience syzygy? In one of two instances: either the Moon is between the Sun and the Earth (that's a new moon, because from our vantage, the Moon is completely black; the far side of the Moon is in full illumination) or the Earth is between the Sun and the Moon (a full moon, when the Sun's rays are lighting the side we see).

Bear in mind that this does not mean perfect alignment. The phases of the moon have nothing to do with the Earth's shadow.

So a perigee-syzygy of the Earth–Moon–Sun system means an alignment that occurs when the Moon is near to the Earth. It could be a full moon. It could be a new moon. Easy, right? Inasmuch as a made-up term from a made-up belief system can have a proper definition, a supermoon generally means a full moon.

WHY ARE THERE SO MANY SUPERMOONS THIS YEAR?

Not every full moon is at perigee (or its opposite, apogee, when the Moon is farthest from the Earth). The lunar cycle—the number of days it takes the Moon to experience each of its phases, new moon to new moon—lasts about 29 and a half days. Every 14 lunar cycles, the full moon coincides with perigee.

Supermoons tend to come in threes, however. The reason is that the full moons preceding and succeeding perigee-syzygy are still inordinately close to the Earth, and thus appear a lot larger than normal. Moons that are 224,641 miles or closer to the Earth are considered supermoons. The result: a supermoon trifecta, three in a row.

So if you've experienced supermoon overload this year, take comfort that it'll be more than a year before you have to hear the term again. Enjoy it: 2016 has been a year of wildly unexpected and sometimes awful events. Something as predictable and wonderful as the cosmos can be a great comfort indeed.

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Look Up! Residents of Maine and Michigan Might Catch a Glimpse of the Northern Lights Tonight
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The aurora borealis, a celestial show usually reserved for spectators near the arctic circle, could potentially appear over parts of the continental U.S. on the night of February 15. As Newsweek reports, a solar storm is on track to illuminate the skies above Maine and Michigan.

The Northern Lights (and the Southern Lights) are caused by electrons from the sun colliding with gases in the Earth’s atmosphere. The solar particles transfer some of their energy to oxygen and nitrogen molecules on contact, and as these excited molecules settle back to their normal states they release light particles. The results are glowing waves of blue, green, purple, and pink light creating a spectacle for viewers on Earth.

The more solar particles pelt the atmosphere, the more vivid these lights become. Following a moderate solar flare that burst from the sun on Monday, the NOAA Space Weather Prediction Center forecast a solar light show for tonight. While the Northern Lights are most visible from higher latitudes where the planet’s magnetic field is strongest, northern states are occasionally treated to a view. This is because the magnetic North Pole is closer to the U.S. than the geographic North Pole.

This Thursday night into Friday morning is expected to be one of those occasions. To catch a glimpse of the phenomena from your backyard, wait for the sun to go down and look toward the sky. People living in places with little cloud cover and light pollution will have the best chance of spotting it.

[h/t Newsweek]

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Kevin Gill, Flickr // CC BY-2.0
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10 Facts About the Dwarf Planet Haumea
Kevin Gill, Flickr // CC BY-2.0
Kevin Gill, Flickr // CC BY-2.0

In terms of sheer weirdness, few objects in the solar system can compete with the dwarf planet Haumea. It has a strange shape, unusual brightness, two moons, and a wild rotation. Its unique features, however, can tell astronomers a lot about the formation of the solar system and the chaotic early years that characterized it. Here are a few things you need to know about Haumea, the tiny world beyond Neptune.

1. THREE HAUMEAS COULD FIT SIDE BY SIDE IN EARTH.

Haumea is a trans-Neptunian object; its orbit, in other words, is beyond that of the farthest ice giant in the solar system. Its discovery was reported to the International Astronomical Union in 2005, and its status as a dwarf planet—the fifth, after Ceres, Eris, Makemake, and Pluto—was made official three years later. Dwarf planets have the mass of a planet and have achieved hydrostatic equilibrium (i.e., they're round), but have not "cleared their neighborhoods" (meaning their gravity is not dominant in their orbit). Haumea is notable for the large amount of water ice on its surface, and for its size: Only Pluto and Eris are larger in the trans-Neptunian region, and Pluto only slightly, with a 1475-mile diameter versus Haumea's 1442-mile diameter. That means three Haumeas could fit sit by side in Earth—and yet it only has 1/1400th of the mass of our planet.

2. HAUMEA'S DISCOVERY WAS CONTROVERSIAL.

There is some disagreement over who discovered Haumea. A team of astronomers at the Sierra Nevada Observatory in Spain first reported its discovery to the Minor Planet Center of the International Astronomical Union on July 27, 2005. A team led by Mike Brown from the Palomar Observatory in California had discovered the object earlier, but had not reported their results, waiting to develop the science and present it at a conference. They later discovered that their files had been accessed by the Spanish team the night before the announcement was made. The Spanish team says that, yes, they did run across those files, having found them in a Google search before making their report to the Minor Planet Center, but that it was happenstance—the result of due diligence to make sure the object had never been reported. In the end, the IAU gave credit for the discovery to the Spanish team—but used the name proposed by the Caltech team.

3. IT'S NAMED FOR A HAWAIIAN GODDESS.

In Hawaiian mythology, Haumea is the goddess of fertility and childbirth. The name was proposed by the astronomers at Caltech to honor the place where Haumea's moon was discovered: the Keck Observatory on Mauna Kea, Hawaii. Its moons—Hi'iaka and Namaka—are named for two of Haumea's children.

4. HAUMEA HAS RINGS—AND THAT'S STRANGE.

Haumea is the farthest known object in the solar system to possess a ring system. This discovery was recently published in the journal Nature. But why does it have rings? And how? "It is not entirely clear to us yet," says lead author Jose-Luis Ortiz, a researcher at the Institute of Astrophysics of Andalusia and leader of the Spanish team of astronomers who discovered Haumea.

5. HAUMEA'S SURFACE IS EXTREMELY BRIGHT.

In addition to being extremely fast, oddly shaped, and ringed, Haumea is very bright. This brightness is a result of the dwarf planet's composition. On the inside, it's rocky. On the outside, it is covered by a thin film of crystalline water ice [PDF]—the same kind of ice that's in your freezer. That gives Haumea a high albedo, or reflectiveness. It's about as bright as a snow-covered frozen lake on a sunny day.

6. HAUMEA HAS ONE OF THE SHORTEST DAYS IN THE ENTIRE SOLAR SYSTEM.

If you lived to be a year old on Haumea, you would be 284 years old back on Earth. And if you think a Haumean year is unusual, that's nothing next to the length of a Haumean day. It takes 3.9 hours for Haumea to make a full rotation, which means it has by far the fastest spin, and thus shortest day, of any object in the solar system larger than 62 miles.

7. HAUMEA'S HIGH SPEED SQUISHES IT INTO A SHAPE LIKE A RUGBY BALL.

haumea rotation gif
Stephanie Hoover, Wikipedia // Public Domain

As a result of this tornadic rotation, Haumea has an odd shape; its speed compresses it so much that rather than taking a spherical, soccer ball shape, it is flattened and elongated into looking something like a rugby ball.

8. HIGH-SPEED COLLISIONS MAY EXPLAIN HAUMEA'S TWO MOONS.

Ortiz says there are several mechanisms that can have led to rings around the dwarf planet: "One of our favorite scenarios has to do with collisions on Haumea, which can release material from the surface and send it to orbit." Part of the material that remains closer to Haumea can form a ring, and material further away can help form moons. "Because Haumea spins so quickly," Ortiz adds, "it is also possible that material is shed from the surface due to the centrifugal force, or maybe small collisions can trigger ejections of mass. This can also give rise to a ring and moons."

9. ONE MOON HAS WATER ICE—JUST LIKE HAUMEA.

Ortiz says that while the rings haven't transformed scientists' understanding of Haumea, they have clarified the orbit of its largest moon, Hi'iaka—it is equatorial, meaning it circles around Haumea's equator. Hi'iaka is notable for the crystalline water ice on its surface, similar to that on its parent body.

10. TRYING TO SEE HAUMEA FROM EARTH IS LIKE TRYING TO LOOK AT A COIN MORE THAN 100 MILES AWAY.

It's not easy to study Haumea. The dwarf planet, and other objects at that distance from the Sun, are indiscernible to all but the largest telescopes. One technique used by astronomers to study such objects is called "stellar occultation," in which the object is observed as it crosses in front of a star, causing the star to temporarily dim. (This is how exoplanets—those planets orbiting other stars—are also often located and studied.) This technique doesn't always work for objects beyond the orbit of Neptune, however; astronomers must know the objects' orbits and the position of the would-be eclipsed stars to astounding levels of accuracy, which is not always the case. Moreover, Ortiz says, their sizes are oftentimes very small, "comparable to the size of a small coin viewed at a distance of a couple hundred kilometers."

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