We’re having a loaded lunar trifecta on Jan. 31
This coming Wednesday we’re having an extremely rare astronomical event over southwest Minnesota. It will be a super bloody blue moon all in the same 20 hours. It’s been over 130 years since this last happened, and it won’t happen again for a heck of a long time!
The term blue moon has been around for hundreds of years, but in the last several years two new slang names have been added to our lexicon regarding the moon; super moon and blood moon. It’s getting to be that we need a lunar scorecard! Let’s take on one moon moniker at a time.
1. Blue moon
No one really knows exactly when the term blue moon originated. In literature it first showed up around 1600 A.D. in England during the time of William Shakespeare. Despite the name it doesn’t have anything to do with the color of the moon. It’s also not a reflection of a sad mental state of Earth’s lunar partner. A blue moon actually has to do with mathematical odds. The synodic period of the moon, or the total time of the phase cycle, is 29.5 days. That’s the time between any particular phase of the moon, for example the time between two full moons.
The time between full moons is 29.5 days, and the average length of a calendar month is a little over 30 days. Because of that we usually only have one full moon in any given month. Inevitably, though, we get two full moons a month, and when that occurs the second full moon is called a blue moon. On average that only happens about every two-and-a-half years. Obviously for it to happen you need to have the first full moon very close to the first of month and the blue moon near the end of the month.
On Jan. 2 of this new year of 2018 we had our first full moon of the month, and this coming Wednesday we’ll have a blue moon. But that won’t be our only blue moon in 2018. In March we’ll have a full moon on the 1st and a blue moon on the 31st. Blue moon in both January and March also means there will be no full moon this February. Two blue moons in a calendar year only happens four to five times a century. The next time we have two blue moons in a calendar year won’t be until 2037.
2. Blood moon
This is now the hip slang term for any total lunar eclipse, mainly because during totality the moon becomes bloody red in color when it crosses into the Earth’s shadow. Its original use came from biblical prophecy involving the end of the world. It just so happens that during the full blue moon this Wednesday it will also turn into a blood moon, as we’ll have a total lunar eclipse. The eclipse will take place early Wednesday morning.
Lunar eclipses or “blood moons” occur when the moon, in its orbit around the Earth, passes through the Earth’s shadow opposite the sun, known also as the umbra shadow. This can only happen during a full moon when our planet lies in a line between the sun and moon. But this doesn’t occur every time there’s a full moon because the moon’s orbit around the Earth is tilted by five degrees to the Earth’s orbit around the sun. Most of the time the full moon misses the Earth’s shadow. It either passes above or below it. Not this time though. Early Wednesday morning the moon will charge right into the umbra shadow and get bloody!
The moon will enter the umbra at 5:48 a.m. as morning twilight begins. It will be completely in the umbra at 6:51 a.m. and the bloody totality begins. Unfortunately, right as the moon makes it to the middle of the Earth’s shadow it will also be setting below the northwest horizon, with the sun rising shortly thereafter in the east.
The good news for bloody moon fans is that the moon being in the umbra combined with the usual reddening of the moon when it’s close to the horizon will make the moon extra bloody!
3. Super moon
Not only will the full moon be a bloody blue moon, it will also be considered a “super”moon. Back in 1979 astrologer Richard Nolle coined the term “super moon” which has now become widely used and loved. Nolle arbitrarily defined a super moon as a full moon which occurs when the moon is within 90 percent of its closest approach to Earth in any given orbital cycle. In order for a full moon to earn the right to be called a super moon it has to be within 226,000 miles from Earth. The moon’s 27.3 day orbit around the Earth is not quite a perfect circle, but rather an ellipse. Because of that ellipse shape, every month the moon has a minimum distance to the Earth at just over 221,000 miles called perigee, and its maximum distance dubbed apogee at nearly 253,000 miles from our terrestrial home. Apogee and perigee don’t coincide with a particular phase of the moon, because the period of the moon’s orbit around Earth is more than two days shorter than the cycle of phases, otherwise known as the synodic period.
The full moon this Wednesday will be right around 224,000 miles from Earth, earning it the right to be called a super moon, at least according to Richard Nolle. Without a doubt the moon will be a little bigger and brighter in the sky than a usual full moon is, but only about 7 percent larger and 15 percent brighter than average. In my book at least I wouldn’t exactly call that super, but who am I to get in the way of media hype! In my opinion, the hype is the result of the large appearance any full moon has when it’s close to the horizon around rising and setting times. This is an optical illusion that I’ll tell you about some other time.
So there you have it! Enjoy the super bloody blue full moon this coming Wednesday!
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/St Paul and is author of the book, “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications available at bookstores at http://www.adventurepublications.net.