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You Can See a Rare Total Eclipse of a Red Super Harvest Moon

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On Sunday September 27, something rare and wonderful will happen: the Moon will be full, it will be as near to us as it gets, and it will line up perfectly with the Earth and Sun. The result will be a rare total super harvest moon eclipse, when a giant, full Moon will turn a stunning shade of red.

In celestial terms, that's like a Super Bowl played by Academy Award nominees, with the winner revealing who killed Laura Palmer. It's the only one in a 51-year period; the last supermoon eclipse occurred in 1982, and the next won't come around until 2033. Don't miss it or you'll have to wait 18 years.

WHAT IS GOING ON UP THERE?

We've known for at least 2500 years what a lunar eclipse is thanks to Anaxagoras, a Greek philosopher, who worked out the mechanics in the 5th century BCE. Though we've been recording eclipses for millennia, they never fail to inspire a sense of awe and wonder.

So how does this rare total super harvest moon eclipse come about? You've probably noticed that the Moon appears to be different sizes at various points throughout the year. This is because the Moon's orbit around the Earth is not circular but elliptical. When the Moon is nearest to the Earth on its orbit, it is at "perigee." When it is farthest away, it is at "apogee." At perigee, the Moon appears giant, and at apogee, small.

Note that this is unrelated to the Moon's phases, which are determined by the relative positions of the Sun, Earth, and Moon. For example, when the Earth is between the Moon and the Sun, you see a full moon, because we're looking at the fully sunlit side of the Moon. The three bodies rarely line up exactly, but when they do, you get a total lunar eclipse.

Bringing the two concepts together: When the Moon's phase is full and it is at perigee (i.e. closest to the Earth, and thus giant), you get what astronomers call perigee-syzygy, or, colloquially, a "supermoon." Now add the date to the equation: September is harvest time for farmers, making a full moon that month a "harvest moon." Why? In the days before light bulbs, farmers could use this extra moonlight to harvest crops late into the night.

This weekend the Moon will be full, it will be at perigee, and it will line up perfectly with the Earth and Sun. Because all of this is happening in late September, you get a total super harvest moon eclipse! It's like a moon named by the people who make sequels to Street Fighter.

WHEN TO LOOK UP

On September 27 at 9:07 p.m. EST, the Moon will begin traveling through the Earth's shadow. At 10:11 p.m., the Moon will be fully eclipsed, and will turn an amazing shade of red. The show will last 72 minutes.

But why will it be red? From the vantage point of the Moon, the Earth will appear to be moving across the Sun. Once the Earth is directly between the Moon and the Sun, as NASA evocatively explains, "the darkened terrestrial disk is ringed by every sunrise and every sunset in the world, all at once." The copper sky filters into the shadow of the Earth and is projected onto the white disk that is the Moon. Here's a shockingly crimson Moon as seen from Australia in August 2007.

Image credit: Martin Pugh via NASA
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Space
Here's Where You Can Watch a Livestream of Cassini's Final Moments
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It's been a road trip like no other. After seven years and 2.2 billion miles, the NASA orbiter Cassini finally arrived at the Saturn system on June 30, 2004. Ever since, it's been capturing and transmitting valuable data about the distant environment. From sending the Huygens probe to land on the moon Titan to witnessing hurricanes on both of the planet's poles, Cassini has informed more than 3000 scientific papers.

It's been as impressive a mission as any spacecraft has ever undertaken. And tomorrow, Cassini will perform one last feat: sacrificing itself to Saturn's intense atmosphere. Project scientists are deliberately plunging it into the planet in order to secure just a little more data—and to keep the spacecraft, which is running low on fuel, from one day colliding with a Saturnian moon that might harbor life.

Because it won't have time to store anything on its hard drive, Cassini will livestream its blaze of glory via NASA. The information will be composed mostly of measurements, since pictures would take too long to send. Instead, we'll get data about Saturn's magnetic field and the composition of its dust and gas.

"As we fly through the atmosphere, we are able to literally scoop up some molecules, and from those we can figure out the ground truth in Saturn’s atmosphere," Scott Edgington, a Cassini project scientist, told New Scientist. "Just like almost everything else in this mission, I expect to be completely surprised."

The action will kick off at 7 a.m. EDT on Friday, September 15. Scientists expect to say goodbye to Cassini less than an hour later. 

While you wait for Cassini's grand finale, you can check out some essential facts we've rounded up from Saturn experts. And keep your eyes peeled for a full recap of Cassini’s historic journey: Mental Floss will be in the control room at the Jet Propulsion Laboratory in Pasadena, California, to offer a firsthand account of the craft's final moments in space. 

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Big Questions
What Are the Northern Lights?
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Over the centuries, many have gazed up at one of the Earth’s most fascinatingly beautiful natural wonders: the Northern Lights. In the past couple of weeks, some lucky American stargazers have gotten the chance to see them from their very own backyards—and could again this week, according to Thrillist. But what are they?

Before science was able to get a read on what exactly was happening in the night sky, ancient tribes had their own theories for what caused the jaw-dropping light show. Many early beliefs had roots in religion, such as that the light was a pathway souls traveled to reach heaven (Eskimo tribes) or that the light was an eternal battle of dead warriors (Middle-Age Europe). Early researchers were a bit more reasonable in their approximations, and most surrounded the idea of the reflection of sunlight off the ice caps. In 1619, Galileo Galilei named the lights the aurora borealis after Aurora, the Roman goddess of morning, after concluding they were a product of sunlight reflecting from the atmosphere.

Today, scientists have come to the general agreement that the lights are caused by the collision of electrically charged solar particles and atoms from our atmosphere. The energy from the collisions is released as light, and the reason it happens around the poles is because that's where the Earth’s magnetic field is the strongest. In 2008, a team at UCLA concluded that “when two magnetic field lines come close together due to the storage of energy from the sun, a critical limit is reached and the magnetic field lines reconnect, causing magnetic energy to be transformed into kinetic energy and heat. Energy is released, and the plasma is accelerated, producing accelerated electrons.”

"Our data show clearly and for the first time that magnetic reconnection is the trigger," said Vassilis Angelopoulos, a UCLA professor of Earth and Space Sciences. "Reconnection results in a slingshot acceleration of waves and plasma along magnetic field lines, lighting up the aurora underneath even before the near-Earth space has had a chance to respond. We are providing the evidence that this is happening."

The best time to see the Northern Lights is during the winter, due to the Earth’s position in relation to the sun (shorter days means darker night skies). And by the way, it’s not just the North Pole that puts on a show—there are Southern Lights, too. There are also aurora borealis on other planets—including Mars—so rest assured that future generations born “abroad” will not miss out on this spectacular feat of nature.

Haven’t seen them yet? Traditionally, the best places to catch a glimpse of the Northern Lights are in Iceland, Sweden, Norway, Finland, Greenland, northern Canada, and Alaska. Maybe you'll get lucky this week and sneak a peek from your very own window. Check out Aurorasaurus for regular updates on where they are showing.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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