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Once in a blue moon? Not if you know when (and where) to look. From the rare event that inspires this iconic phrase to the so-called "supermoon," the moon can put on quite a show for those of us down on Earth.
Did you know? The moon is 249,480 miles away, but despite that distance, it plays an important role for Earth — from helping to lock our planet in position as it rotates around the sun to regulating the tides. The moon gives our planet steadiness and rhythm, but our view of the moon is always changing. We can see the various phases of the moon based on where it's at on its revolution around Earth. The consistency of those movements gives us a pretty good idea of what to expect when we look up at night, but sometimes the moon can surprise us. Here are five rare lunar events to watch for in the night sky.
Blood Moon
A blood moon is a lot less scary than it sounds. The name comes from the color of the moon, which can range from a muddy brown to a bright red. This reddish color appears when the moon is in a lunar eclipse. A lunar eclipse is when the Earth passes between the sun and the full moon — blocking the light from the sun that usually illuminates the moon's surface. The only light hitting the moon comes from the sunrises and sunsets on Earth, giving it that distinct reddish hue.
Seeing the moon turn red can be a little unsettling, so it's no wonder that many ancient cultures once thought the blood moon was a bad omen. The Inca people believed a blood moon occurred when a jaguar attacked and ate the moon. Ancient Mesopotamians, on the other hand, believed the blood moon was an omen that their king was in danger. To counter the threat of the moon, they'd hide the true king and put a false king in his place until the moon returned to normal. Native American tribes viewed the red color as a sign that the moon was wounded, so they would sing healing songs to it. The next blood moon will occur in May 2021, so make sure you mark your calendar.
Blue Moon
The phrase "once in a blue moon" alludes to the fact that blue moons are a pretty rare phenomenon, but there are actually two ways a blue moon can appear in the night sky. The first is when the moon actually appears to turn blue as opposed to its usual white or yellowish color. The moon can appear to be blue due to dust in the atmosphere. The dust affects how the light reaches our eyes, which makes the moon appear blue.
On the other hand, the term "blue moon" also refers to a month in astronomy that has two full moons in it. Most months only have one full moon since the lunar cycle (from a new moon to a full moon) takes roughly 29.5 days. Occasionally, the calendar will align and allow us two full moons in a single month. That second full moon is referred to as a blue moon. It only happens once every two or three years. The next blue moon will occur on October 31, 2020, which is perfect timing for that spooky werewolf costume.
Black Moon
While blue moons occur when there are two full moons in a single month, black moons are the exact opposite. Black moons most commonly refer to the second new moon in a single month, occurring on average every 32 months. Most of the time we get a single new moon each month due to the time it takes for the moon to travel around Earth. New moons happen when no sunlight shines on the moon's surface to illuminate it. There isn't much to see when you look up, although the moon is still there. When the new moon is over, you'll see a tiny sliver of the moon as it starts to receive the reflected light of the sun again.
And there is actually another lunar phenomenon that might be referred to as a black moon — when there is no new moon in the month. This is an even rarer occurrence, which only happens about once a decade. It is most likely to happen in the month of February since it has fewer days. The second new moon in a month will happen on April 30, 2022.
Harvest Moon
A harvest moon is more than the title of a great Neil Young song — it's also the name given to the full moon closest to the autumnal equinox. This is also the traditional time of the harvest when farmers would work in the fields and harvest their crops. The full moon allowed the farmers to work through the night, thanks to the extra hours of light overhead. Since the autumnal equinox happens every year, there is a harvest moon every year as well, although the date changes.
Harvest moons marked an important time of the year for European agricultural societies, often marked by celebrations, and it was a celebrated event in China as well. This festival happened in mid-autumn with lots of games and delicious moon cakes. This year's harvest moon will occur on October 1, 2020 if you want to get your moon cakes ready.
Supermoon
Love looking at the moon? Then the supermoon is the lunar event for you. Richard Nolle coined the term "supermoon" in 1979 to describe a moon that appears to be bigger and brighter in the sky than normal. It appears bigger because it's actually closer to Earth. This is because the orbit of the moon around the Earth isn't perfectly symmetrical. There are times when the moon is slightly closer, which makes it appear about 12% bigger and an impressive 25% brighter than usual.
Want to impress your friends? Let them know that the astronomical term for a supermoon is a perigee-syzygy. "Perigee" is the term for the point when the moon is closest to the earth. "Syzygy" is the astronomical term for the alignment of the sun, the moon, and the Earth, which happens at every full and new moon. Supermoons are great for stargazers who want to get a better look at the surface of the moon with their telescope. They aren't as uncommon as other lunar events either. In fact, there will be four supermoons in 2021, with the first one happening on March 28. Mark your calendars!