Friday the 13th's rare 'Harvest Micro Moon' is quite literally not a big deal

What is going on with my moon?

moon

The Full Moon

Regular-style.NASA

This post has been updated, because you still care about the moons.

Blue moons, black moons, pink moons, strawberry moons, micromoons, supermoons. For some reason, your news aggregation algorithm of choice thinks you really really really want to know all about these moons. "Catch This Weekend's AMAZING SUPERMOON," one headline (or, like, 500 of them) will announce. "The Supermoon Isn't Actually A Big Deal And You're All Ruining Astronomy," another will grouse.

One recent example was the super worm moon on March 20. It was the third and last full supermoon of 2019, which didn't necessarily mean it was a moon particularly worth your gaze. We get these super-duper-lunar events (remember the super blood wolf moon eclipse?) by smashing together all the qualifiers we've historically used to keep track of full moons throughout the year, and in the age of the internet, we can go a little overboard.

On Friday, September 13, we'll be treated to a super-spooky (?) sounding Harvest Micromoon—ostensibly a rare event, but one that is quite literally not a big deal. Here's everything you need to know about what's going to show up in the sky on Friday the 13th. Consider this your go-to resource for all moon-related news.

Regular Ol' Full Moon

Look, it's okay if you don't know. There are probably loads of folks who walk around pretending they totally know why that thing in the sky seems to get bigger and smaller at regular intervals who totally do not.

The moon orbits Earth, and it’s tidally locked—that means it always shows us the same face, instead of twirling around like our planet does. That’s why you can always see the man on the moon (or the moon rabbit, depending on your cultural preferences) even as it spins around us. But while the moon is big and bright in the sky when it’s full, that’s only because it’s reflecting light from the sun. The moon is also always moving, so it’s getting hit with sunlight at different angles. It’s invisible to us during the “new moon,” because our satellite is parked right between us and the sun; the so-called dark side of the moon is lit up like a Vegas, but the side we can see is in shadow. A full moon happens when the earth is right between the sun and the moon, so sunlight hits the part we can see. And all the other phases are just the transition from one of those extremes to the other.

Super Moon

The moon isn't always exactly the same distance from Earth, because its orbit isn't perfectly circular. We call the closest point perigee, and the most distant point is apogee. 2018's closest perigee and most distant apogee both happened in January, and the difference was about 30,000 miles. The average distance between the two bodies is about 238,855 miles, so while not insignificant, this shift is far from earth-shattering.

The reason you care about this middling change in distance is that it turns a moon super. When a full moon happens close to perigee, it's going to look a smidge bigger. Maybe. If you're lucky. Honestly, the difference is not that profound, but if you're in a position to photograph the supermoon next to something that shows the slight increase in scale, it can look pretty cool. Not all supermoons are created equal, by the way: March 2019's super worm moon was super because the date of the full moon lined up with the closest the moon would get to us during March, but the moon was actually at its closest for the year in February.

And just to really remind you that words are meaningless and the moon is always just the moon no matter what we decide to call it, July 2019's black moon—otherwise known as a new moon, which is not visible from the ground—was also a supermoon. Yes, the moon made its closest approach to Earth on a night we couldn't see it. Just because you can't snap a pic for your Instagram doesn't mean the moon isn't super.

Micro Moon

See above; it's the opposite of the super one. Size isn't everything. In a previous version of this article, I wrote that while we had such a moon coming up in September 2019, we probably wouldn't see tons of news outlets crowing over the Micro Full Corn Moon. I was only half right: There are plenty of headlines crowing, though they've decided to dub it the Harvest Micromoon instead (more on alternate monthly moon names can be found below).

Friday the 13th

One of the reasons the aforementioned puny-looking moon is getting buzz is that it's falling on Friday the 13th, a day long considered unlucky in many Western cultures. Yes, it's true that a full moon on Friday the 13th is not something that happens very often: the last one that was visible nationwide (people in different time zones sometimes don't see the moon at true fullness on the same calendar day) was 2000, and the next won't be until 2049. But that's not spooky; it's math. Because of the way the Gregorian calendar works, the 13th day of the month falls on a Friday anywhere from 1 to 3 times a year. There are 12 to 13 full moons in a year. Those two things happen to sync up regularly, but not often.

Of course, it's not surprising that we get a little excited, as a culture, when a full moon falls on Friday the 13th. We have a long history of associating supernatural events and even run-of-the-mill mental illness with the lunar cycle, though even the latter has been pretty thoroughly debunked. Similar research has checked out the idea that Friday the 13th might be full of accidents and misfortunate events—not because of bad luck, but because superstitious folks are prone to act strangely when they expect terrible things to happen—and found little cause for alarm. That being said, allowing superstition to fill you with fear can make your life unpleasant, or even dangerous, because the human mind is a powerful chaos agent. Some experts suggest using positive superstitious rituals (like throwing salt over your shoulder to ward off bad luck) to negate any anxiety you have over the power of the calendar.

Black Moon

You may be familiar with the concept of a blue moon (see below), which rather dramatically refers to the second full moon in a month. A black moon is the same thing, but for the second new moon in a month. This happens about once every three years. What's it look like? Well, it looks like a new moon. That means you can't really see it. But by all means, get out there and do some stargazing.

In case you haven't yet really grasped the fact that all of these moons are just the result of our arbitrary and often nonsensical calendar system, consider this: In some time zones, North America's July 31 new moon actually rose on August 1. That means it wasn't a black moon, because it was the first new moon of August instead of the second new moon of July. Those time zones got their own black moon at the end of August, when we Americans looked up to see our first new moon of the month (which was their second). This is all definitely very important and noteworthy.

New Moon

A black moon may be rare, but what's also rare is a super-duper-look-at-the-moon article about a new moon. Every 29.531 days, the relative positions of the sun, moon, and Earth conspire to leave our satellite—which doesn't produce its own light, but shines thanks to the reflected light of our host star—in the dark. The sun's rays are still striking the moon's surface, but they're hitting the (obviously inappropriately named) dark side that faces away from us. The moon appears to grow and shrink in the sky throughout the month thanks to shifts in its position relative to Earth and the sun. Fun fact: while basically everyone knows what a crescent moon is and why it's so-called, you might not know that the bulbous shape of a moon somewhere between a straight split down its face and a full circle is called "gibbous," from the Latin for hunched or humped.

Blue Moon

In March of 2018, we had our second "blue moon" of that year, to much acclaim. And while that's not necessarily special in an oh-gosh-get-out-and-look-at-it kinda way, it's certainly special: A blue moon is a nickname for when two full moons fall in the same calendar month, and we hadn't previously had two in one year since 1999. We won't have it happen again until 2037. Astronomer David Chapman explained for EarthSky that this is merely a quirk of our calendar; once we stopped doing things based on the moon and started trying to follow the sun and the seasons, we stopped having one reliable full moon per month. The moon cycle is 29.53 days long on average, so on most months we still end up with a single new moon and a single full one. But every once in awhile, things sync up so that one month steals a full moon from another. In 2018 (and in 1999, and again in 2037) both January and March stacked full moons on the first and last nights of the month, leaving February in the dark.

Getting two blue moons a year is rare, but we have individual blue moons every few years. The next one will occur on Halloween of 2020, so you can expect people to really lose their minds over that one. Also, fun fact: not actually blue. A moon can indeed take on a moody blue hue, but this only happens when particles of just the right size disperse through the sky—and it has nothing to do with the moon's status as "blue." Big clouds of ash from volcanic eruptions or fires can do the trick, but it doesn’t happen often, and the stars would certainly have to align for two such rare instances to occur at once.

Blue Moons that are not actually Blue Moons (see: May 18, 2019)

If you're good at counting, you may have asked yourself how we could possibly see a blue moon—the second full moon in a month—in mid-May. The answer is that we couldn't. The blue moon of May 18, 2019 was not the blue moon you were looking for. The moon is full every 29.5 days, so blue moons are only even possible on the last day or two of any given month. The full moon on May 18 was the first and only full moon for the month of May 2019.

And yet.

Surprise! There's another kind of moon that some farmer's almanacs refer to as blue. Just as there's typically one full moon a month, there are generally three full moons a season. And just as there are sometimes two full moons in a month due to our calendar almost-but-not-quite following the lunar cycle (ugh) there are sometimes four full moons in a season. April 2019's full moon landed right as spring began, leaving enough time for another three (the last rose on June 17, less than a week before summer officially kicked off and long after we'd all started acting like spring was dead and buried). Some breathlessly referred to this as a rare occurrence, but it happens every couple of years, which is not a lot of time.

Weirdly, the blue moon moniker is applied not to the fourth full moon in a season (which is the one that only happens once-in-a-you-know-what) but to the third. Why? Who knows. What's the fourth full moon in a season called? A full moon. ¯_(ツ)_/¯

Similarly, the term "black moon" most commonly refers to the second new moon in a calendar month, but can also refer to the third new moon in a season with four of them. The phrase has also historically been applied to months without full moons and months without new moons, which can only happen in February (the shortest month). Both of these circumstances happen about once every 19 years.

Flower Moons, Worm Moons, Pink Moons, Strawberry Moons…

Sometimes you'll see a headline that promises a moon with so many qualifiers it makes your head spin. A superblueblood worm moon, mayhaps? Or a super blood wolf moon? Lots of websites will tell you that "wolf moon" is the traditional name of the first full moon of the year in "Native American" cultures, which is kind of a weird thing to claim given that there are 573 registered Tribal Nations in the U.S. alone today, not to mention historically. The idea that hungry, howling wolves were such a universal constant in January that all of North America with its disparate cultures, geographies, and languages spontaneously came up with the same nickname is—well, it's dumb. It's a dumb idea.

The Full Harvest Moon is so-named for being the full moon in closest proximity to the autumnal equinox (which usually falls in September, but sometimes falls in October). When the September full moon isn't a Harvest moon, it's often referred to as a Full Corn moon due to its overlap with corn harvesting. But this is another great example of how bizarre it is to cite full moon names as coming from "Native American" cultures: even the Farmer's Almanac says that some tribes called it the Barley Moon, because they were harvesting barley instead of corn, while other traditional names translate into commentary on the color of plums, notes on local deer behavior, and thoughts on the hair growth of calves.

Many cultures have traditional names for the full moon in a given month or season, so there's quite a list to draw from if you're trying to really plump up a story on a slightly-bigger-than-average view of the moon. But these are all based on human calendars and activities and folklore; you will not go outside and see a pink moon in April (or a moon full of beavers in November, for that matter), though I wish it were so. Full moons can turn up with a slight tint, but that has nothing to do with what month it is.

Blood Moon

Objectively the most metal moon (sorry, black moon), these only occur during total lunar eclipses (which can happen a few times a year in any given location). When the moon slips through our shadow, we give it a reddish cast. The moon can also look orange whenever it's rising or setting, or if it hangs low in the horizon all night—the light bouncing off of it has to travel through thicker atmosphere there, which scatters more blue light away. But you'll probably only see that deep, sinister red during an eclipse.

A lot of headlines about moons are just silly (you do not need to be particularly excited about a blue moon, it just looks like a regular ol' moon), but you should definitely roll out of bed to look at a blood moon if one is going to be visible in your region. But anyone who crams both "blood" and "eclipse" into their moniker for a moon is just trying to win the search engine optimization game; a blood moon is just a lunar eclipse that's going through a goth phase. Ryan F. Mandelbaum at Gizmodo makes the case that we should really just stop throwing the phrase "blood moon" around and call them lunar eclipses, which is tough but fair, because they're lunar eclipses and not evidence of bloody battles between the sky gods.

Super Moon

Super moon

This is a "super moon" rise from 2017. Using a 1200mm lens makes the moon appear larger in the scene.Stan Horaczek

Paschal Moon

You may have heard that April's pink moon was also a Paschal moon. This is true! That just means it was used to determine the date of Easter Sunday. All of this is just calendar nonsense. In fact, the fall of a full moon just a few hours after the 2019 Vernal Equinox made this calendar nonsense way more confusing than usual. We refuse to go into this calendar nonsense further.