Here's why you don't want to miss this week's super-rare lunar eclipse

A celestial event unlike anything we’ve seen in over 30 years is happening Sunday night in the form of a supermoon total lunar eclipse.

While we only get about one to two total lunar eclipses a year, a supermoon total lunar eclipse comes around just four or five times a century.

The event will begin at 9:07 p.m. ET on Sept. 27 and extend into the early morning of the following day. In total, the eclipse will last roughly 3.5 hours.

You can learn more about how to watch it here.

During that time, the moon will adopt a deep-red hue, which is why a total lunar eclipse is sometimes referred to as a “blood moon.” What’s more, the moon will be closer to Earth than at any other time this year, making it what we call a supermoon.

But this super blood moon isn’t the only reason Sunday’s even is so special. The event is also the last in a series of four consecutive total lunar eclipses that began in April 2014.

A series like this is called a tetrad, and it marks four total lunar eclipses that occur back-to-back and are separated by about six months.

Some superstitious folks think the lunar tetrad is a sign of the end of the world. Don’t worry: In reality, these events are merely consequences of celestial geometry. There have been tetrads in the past and there will be tetrads in the future.

Using geometric models, astronomers have calculated that between 2000 BCE and 3000 CE there will be 3,479 total lunar eclipses. Of those, less than 600 will fall or have fallen into a tetrad.

The next tetrad series we’ll see won’t begin until the year 2032.

Roadcrusher at English WikipediaA harvest moon. Its orange colour is due to its closeness to the horizon, rather than being unique to harvest moons.

What’s more, the full moon that you see Sunday evening is what is called a harvest moon. By definition, there is always one harvest moon a year: It’s the full moon that appears closest in time to the autumnal equinox, which marks the first day of fall.

The harvest moon marked an important turning point in the agricultural year for our ancestors. That’s because before the autumnal equinox, the moon rises about 50 minutes later each day. But after fall begins, that difference drops to 25 to 30 minutes, which means there are some extra minutes of daylight that farmers used to harvest their crops.

Since the autumnal equinox took place Wednesday, Sept. 23, this Sunday’s event is not just a supermoon, or an upcoming total lunar eclipse, but a mega harvest moon eclipse, as the experts at online observatory Slooh put it. Slooh will be hosting a live broadcast of the eclipse starting at 8:00 p.m. ET Sept. 27. The broadcast will include commentary from expert Slooh astronomers and will take questions from the public who tweet #SloohEclipse with their question.

The last time we saw a supermoon total lunar eclipse was in 1982. The next time won’t be until 2033. You don’t want to miss it!

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