A Rare Blue Moon Will Light Up the Night Sky This Halloween

Halloween will be even spookier this year.
Halloween will be even spookier this year.
VladGans/iStock via Getty Images

Wolves, werewolves, and people dressed as werewolves will have a bona fide full moon to howl at this Halloween. And it’s not just any full moon—it’s a blue moon.

What Is a Blue Moon?

Since a complete lunar cycle is 29.5 days long, this usually works out to one full moon per calendar month. If a full moon occurs on the first or second day of the month, however, there could technically be another one within the same month. When that happens—about once every 2.5 to 3 years, according to the Farmers’ Almanac—the second full moon is called a “blue moon.”

But up until the mid-20th century, blue moons had a different definition. The Maine Farmers’ Almanac and similar publications used to count full moons by season, so a year with 13 full moons meant that one season would have four (not three) full moons. To avoid messing with full moon nicknames that were tied to certain times of year (e.g. the “moon before Yule”), the third full moon in a season of four was named a “blue moon.”

In a 1943 column for Sky & Telescope, Laurence J. Lafleur mentioned that blue moons occur when a year has 13 full moons, but he didn’t go into detail about how the Maine Farmers’ Almanac determined which moon was, in fact, the blue one. Three years later, another Sky & Telescope author, James Hugh Pruett, wrote an article in which he incorrectly assumed that the blue moon was the second full moon in a month with two. The magazine repeated Pruett’s rule in future stories, and it eventually caught on with the general public.

Why Is It Called a “Blue Moon”?

Just like a pink moon isn’t pink and a worm moon isn’t crawling with worms, a blue moon isn’t actually blue. One theory holds that the name is derived from the Old English word belewe, or “to betray”—perhaps since blue moons betray the normal schedule of full moons. This lunar rarity is also said to be the origin of the phrase once in a blue moon.

The moon actually has appeared blue in the past. After a massive volcanic eruption, the ash in the sky can sometimes block red light particles, giving the moon a bluish tint. According to NASA, this happened after Indonesia’s Krakatoa erupted in 1883, and again when Mexico’s El Chichón spewed its molten guts a century later.

When Can I See October’s Blue Moon?

October's first full moon, the harvest moon, is coming on Thursday, October 1. The second one, the blue moon, will peak on Saturday, October 31, at 10:49 a.m. EST, so you’ll be able to see it before the sun rises or after it sets. Since a full moon on Halloween only happens once every 19 years or so, cross your fingers for clear skies that night.

Amazon's Under-the-Radar Coupon Page Features Deals on Home Goods, Electronics, and Groceries

Stock Catalog, Flickr // CC BY 2.0
Stock Catalog, Flickr // CC BY 2.0

This article contains affiliate links to products selected by our editors. Mental Floss may receive a commission for purchases made through these links.

Now that Prime Day is over, and with Black Friday and Cyber Monday still a few weeks away, online deals may seem harder to come by. And while it can be a hassle to scour the internet for promo codes, buy-one-get-one deals, and flash sales, Amazon actually has an extensive coupon page you might not know about that features deals to look through every day.

As pointed out by People, the coupon page breaks deals down by categories, like electronics, home & kitchen, and groceries (the coupons even work with SNAP benefits). Since most of the deals revolve around the essentials, it's easy to stock up on items like Cottonelle toilet paper, Tide Pods, Cascade dishwasher detergent, and a 50 pack of surgical masks whenever you're running low.

But the low prices don't just stop at necessities. If you’re looking for the best deal on headphones, all you have to do is go to the electronics coupon page and it will bring up a deal on these COWIN E7 PRO noise-canceling headphones, which are now $80, thanks to a $10 coupon you could have missed.

Alternatively, if you are looking for deals on specific brands, you can search for their coupons from the page. So if you've had your eye on the Homall S-Racer gaming chair, you’ll find there's currently a coupon that saves you 5 percent, thanks to a simple search.

To discover all the deals you have been missing out on, head over to the Amazon Coupons page.

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Uranus Reaches Opposition on Halloween in 2020

Christine Schmitt, Flickr // CC BY-NC-ND 2.0
Christine Schmitt, Flickr // CC BY-NC-ND 2.0

Uranus is roughly 1.75 billion miles away from Earth, which makes it difficult to spot without a telescope most nights. But on Saturday, October 31, the seventh planet from the sun will be worth looking for. Uranus reaches opposition that night, making it appear extra bright in the night sky.

What Is Uranus at Opposition?

An opposition occurs when the Earth falls perfectly between another planet and the sun. When this happens, the sun's light appears to fully illuminate the planet's surface, boosting its brightness level to the maximum.

Uranus reaches opposition on October 31 in 2020. During this event, Uranus will hit a limiting magnitude of 5.86, which is about the minimum brightness for what's visible with the naked eye.

How to Look for Uranus at Opposition

Spotting Uranus at opposition will be slightly more difficult in 2020 than in years past. The phenomenon coincides with a full moon that will make dimmer stars and planets—including Uranus—harder to see in the night sky. The planet sits in the constellation Aries, which regrettably appears close to the moon for most of the night.

Uranus should appear as a small, blue-green disc when using a telescope. Even if you have trouble spotting the seventh planet, it will still be worth checking out the night sky on October 31: Halloween this year coincides with a rare blue moon.