As astronomy enthusiasts, we are used to seeing and hearing about space-related events in the news in terms that are meant to “wow” the public, but may otherwise be misleading. Inevitably, we're asked by family members and friends about these events, and often, the response I give is "huh?”.
My introduction to the supermoon was no different...
The first time I heard about a "supermoon" was only a few years ago. 2016, perhaps. Someone had asked me if I was going to take my telescope out to observe the supermoon, and what I thought was going to happen to the earth because of this suddenly massive moon that we'd have. “Do you think the supermoon is going to cause extremely high tides that’ll flood parts of Houston?”
"Huh?" I replied. I didn't know what to say, other than to tell this person it won't be any different than anything else we've already seen.
Of course, when I got home, I quickly jumped on my computer and googled "supermoon." After reading about it, I thought, "oh, that's all it is? A full moon that's at or near the closest point in its orbit?” Since the moon's orbit around the earth isn't a perfect circle, there is a point on that orbit where the moon is closest to the earth, and another point where it is furthest. We label the closest point on that orbit around the earth perigee, and the furthest point is known as apogee. The same terms hold true for earth-orbiting satellites, as well.
Personally, I would have never called anything about the moon "super," per se. You see, I - like most amateur astronomers, am not too terribly fond of our planet’s only large, natural satellite. Sure, if you removed the moon from its orbit, the impact would be catastrophic to human life on earth. But the moon is our enemy - it diminishes our observing conditions any time it's reflecting light in the skies above us. It’s basically a big, round flashlight in the heavens that interferes with our pursuit of deep-sky objects! (Note, I've come to really appreciate the moon after spending some time working on the Astronomical League's Lunar Observing program.)
OK, I get it. Astronomers use terms like "supermoon" to get the public interested in astronomical phenomena all the time. We want to get the public as excited about astronomy as we get. But as I dug into it more, I found out that the term actually owes its existence to an astrologer who coined it in 1979. However, it seems to have stuck, and it's something that I've come to accept whenever people ask me about it. If it keeps people talking about astronomy, then why not embrace it? We just won't mention anything about its astrological origins, though.
So, all of this brings me to a phenomenon you might have heard of coming up on morning of January 31 - the SUPER BLUE BLOOD MOON!!!! It sounds scary enough, but what does it all mean? Well, let's break down each component part:
SUPER - As I described above, the "super” part refers to the supermoon. The moon on this night will be close to perigee, and consequntly, closer to earth. To the well trained lunar observer, the moon will also appear a bit larger. The image below shows the difference between lunar perigee and apogee at different times in 2007.
Photo courtesy of Mike Peel via Wikimedia Commons
BLUE - A blue moon simply refers to the second full moon in a calendar month. Since we saw a full moon early in the month on January 1, the next full moon happens to fall in the same month, on January 31. Hence, the “blue” part of our Super Blue Blood Moon.
(TRIVIA: Did you know that February is the only month in which a blue moon is impossible? Here’s why: The average lunar cycle is 29.53 days. February has 28 days; 29 in a leap year. Even if you had a full moon right at midnight on February 1 of a leap year, the next full moon would occur on March 1 at the earliest. Because a non-leap year February is actually shorter than the lunar cycle, it is possible that February could miss a full moon altogether. That will be the case this February, 2018. Any other calendar month will always have at least one full moon during that month.)
BLOOD - OK, now THIS is where some people's imaginations start to run wild. Someone I know jokingly wondered if the blood moon meant that society is going to break down to the point where it's an apocalyptic free-for-all, akin to what happened in the movie "The Purge." I said I don't know what people are going to do, but if we all go crazy, you can't blame the moon for that. The "blood" part is a reference to the reddish reflection of light we’re going to see from the moon during the lunar eclipse that same night. When the moon passes behind the earth and enters our planet’s umbra, or inner shadow, the only light getting to it is refracted through the earth's atmosphere. This gives the moon a reddish, glow, hence the "blood" portion of this equation. It’s basically the same reddish glow we enjoy at sunset, only now, it’s reflected off the surface of the moon back to us.
|Photo courtesy of Wikicommons|
You add all of these things together, and this is why we’re going to have a “Super Blue Blood Moon” next Wednesday. Based on our location in Houston, the moon will be well on its way to setting on the western horizon by the time it moves into the umbra (or becomes "blood red"), but that doesn't mean it's impossible to see with a clear view.
Go outside and look for the moon to the west on the morning of January 31. The eclipse begins at 4:51am CST, as the moon falls into the earth's shadow. Wait a little longer, and then the fun starts nearly an hour later at 5:48am CST. That's when the moon slides into the earth's umbra and begins its eventual transition into a blood moon. Over the next hour or so, the entire face of the moon will be consumed by the umbral shadow, and will continue to darken, and then turn red. Try your best to observe this early, as you won't have much more time to see the Super Blue Blood Moon before it slinks below the horizon.
If you don’t catch the Super Blue Blood Moon this time around, you’ll have to wait a full 19 years until the next opportunity – January 31, 2037, to be exact. So, get out there and observe!
If you have any questions, email us at [email protected]. Clear skies!
Article by Joe Khalaf, H.A.S. VP and Outreach Chairman