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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
Remembering Comet Hale-Bopp's Unlikely Discovery
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Comet Hale-Bopp was a sensation in the mid-1990s. It was visible to the naked eye for 18 months, shattering a nine-month record previously set in 1811. It inspired a doomsday cult, wild late-night radio theories about extraterrestrials, and plenty of actual science. But a year before it became visible to normal observers, two men independently and simultaneously discovered it in a coincidence of astronomical proportions.

On the night of July 22-23, 1995, Alan Hale was engaged in his favorite hobby: looking at comets. It was the first clear night in his area for about 10 days, so he decided to haul out his telescope and see what he could see. In the driveway of his New Mexico home, he set up his Meade DS-16 telescope and located Periodic Comet Clark, a known comet. He planned to wait a few hours and observe another known comet (Periodic Comet d'Arrest) when it came into view. To kill time, he pointed his telescope at M70, a globular cluster in the Sagittarius system.

Comet Hale-Bopp streaks through a starry night sky.
Comet Hale-Bopp streaks through the sky over Merrit Island, Florida, south of Kennedy Space Center.
George Shelton // AFP // Getty Images

Hale was both an amateur astronomer and a professional. His interest in spotting comets was actually the amateur part, thought it would make his name famous. Hale's day jobs included stints at JPL in Pasadena and the Southwest Institute for Space Research in Cloudcroft, New Mexico. But that night, peering at M70, he wrote, "I immediately noticed a fuzzy object in the field that hadn't been there when I had looked at M70 two weeks earlier." He double-checked that he was looking in the right place, and then started to get excited.

In order to verify that the fuzzy object wasn't something astronomers already knew about, Hale consulted his deep-sky catalogues and also ran a computer search using the International Astronomical Union's computer at Harvard University. Convinced that he had found something new, Hale fired off an email very early on the morning of July 23 to the IAU's Central Bureau for Astronomical Telegrams, telling them what he had found, along with detailed instructions on how to verify it themselves. Hale also tracked the object as it moved, until it moved out of view. It was definitely a comet, and it was definitely new.

Meanwhile, Tom Bopp was in Arizona, also hunting for comets. At the time, Bopp was working at a construction materials company in Phoenix, but he was also an accomplished amateur astronomer, with decades of experience observing deep-sky objects. That night, Bopp vas visiting the remote Vekol Ranch, 90 miles south of Phoenix, known as a great location for dark-sky viewing. He was with a group of friends, which was important because Bopp didn't actually own a telescope.

The Bopp group looked through their various telescopes, observing all sorts of deep-sky objects late into the night. Bopp's friend Jim Stevens had set up his homemade 17.5-inch Dobsonian reflector telescope and made some observations. Stevens finished an observation, then left his telescope to consult a star atlas and figure out what to aim at next. While Stevens was occupied, Bopp peered into Stevens's telescope and saw a fuzzy object enter the field of view, near M70. He called his friends over to have a look.

The Bopp group proceeded to track the fuzzy object for several hours, just as Hale was doing over in New Mexico. By tracking its movement relative to background stars, they (like Hale) concluded that it was a comet. When the comet left his view, Bopp drove to a Western Union and sent a telegram to the Central Bureau for Astronomical Telegrams. (For historical perspective, telegrams were extremely outdated in 1995, but technically they were still a thing.)

Brian Marsden at the Central Bureau received Bopp's telegram hours later, after getting a few followup emails from Hale with additional details. Comparing the times of discovery, Marsden realized that the two men had discovered the comet simultaneously. According to NASA, it was the farthest comet ever to be discovered by amateur astronomers—it was 7.15 Astronomical Units (AU) from our sun. That's 665 million miles. Not bad for a pair of amateurs, one using a homemade telescope!

The Central Bureau verified the findings and about 12 hours after the initial discovery, issued IAU Circular 6187, designating it C/1995 O1 Hale-Bopp. The circular read, in part: "All observers note the comet to be diffuse with some condensation and no tail, motion toward the west-northwest."

Four men smile, posing outdoors next to a large telescope at night.
Comet hunters (L to R): David Levy, Dr. Don Yeomans, Dr. Alan Hale and Thomas Bopp pose next to a telescope during a public viewing of the Hale-Bopp and Wild-2 comets.
Mike Nelson // AFP // Getty Images

Less than a year later, Comet Hale-Bopp came into plain view, and the rest is history. It was a thousand times brighter than Halley's Comet, which had caused a major stir in its most recent appearance in the 1980s. Comet Hale-Bopp will return, much like Halley's Comet, but it won't be until the year 4385. (And incidentally, it was previously visible circa 2200 BCE.)

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NASA/JPL-Caltech/Space Science Institute
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Big Questions
How Many Rings Does Saturn Have?
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NASA/JPL-Caltech/Space Science Institute

Of all the planets surrounded by rings, Saturn is the most famous. These planetary rings are massive enough that Galileo was able to see them using a simple telescope way back in 1610, though it wasn't until half a century later that another scientist was able to figure out what the "arms" Galileo saw actually were. NASA has since called them "the most recognized characteristic of any world in our solar system."

So how many rings does Saturn have, anyway? If you can see them from your backyard, there must be a lot, right?

Scientists don't know for sure exactly how many rings Saturn has. There are eight main, named ring groups that stretch across 175,000 miles, but there are far more than eight rings. These systems are named with letters of the alphabet, in order of their discovery. (Astronomers have known about ring groups A, B, and C since the 17th century, while others are newer discoveries. (The most recent was just discovered in 2009.)

The rings we can see in images of the planet—even high-resolution images—aren't single rings, per se, but are in fact comprised of thousands of smaller ringlets and can differ a lot in appearance, showing irregular ripples, kinks, and spokes. The chunky particles of ice that make up Saturn's rings vary in size from as small as a speck of dust to as large as a mountain.

While the gaps between Saturn's rings are small, the 26-mile-wide Keeler Gap is large enough to contain multiple moons, albeit very small ones. The largest ring system—the one discovered in 2009—starts 3.7 million miles away from Saturn itself and its material extends another 7.4 million miles out, though it's nearly invisible without the help of an infrared camera.

Researchers are still discovering new rings as well as new insights into the features of Saturn's already-known ring systems. In the early 1980s, NASA's Voyager missions took the first high-resolution images of Saturn and its rings, revealing previously unknown kinks in one of the narrower rings, known as the F ring. In 1997, NASA sent the Cassini orbiter to continue the space agency's study of the ringed planet, leading to the discovery of new rings, so faint that they remained unknown until Cassini's arrival in 2006. Before Cassini is sent to burn up in Saturn's atmosphere in September 2017, it's taking 22 dives through the space between the planet and its rings, bringing back new, up-close revelations about the ring system before the spacecraft dives to its death.

Though it's certainly possible to see Saturn's rings without any fancy equipment, using a low-end telescope at your house, that doesn't mean you always can. It depends on the way the planet is tilted; if you're looking at the rings edge-on, they may look like a flat line or, depending on the magnification, you might not be able to see them at all. However, 2017 happens to be a good year to see the sixth planet, so you're in luck.

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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