Supermoon
Lewiston, ME: 2018 is proving to be a stellar year for star and moon gazing. The year started off with a super full wolf moon on the first of January, and is ending with a blue, blood, lunar eclipsed, full, but not supermoon (according to the Farmers’ Almanac) on the 31st.
The Farmers’ Almanac is one of the only outlets not referring to this moon as “super.”
What Makes a Moon “Super?”
n order to be called a “supermoon,” there are specific and exact criteria that have to be met. The moon has to be either in its new or full phase, and the time of this phase needs to coincide with perigee, the moon’s closest point to earth in its orbit. But that distance to earth can vary. The absolute closest the moon can come is 221,429 miles from earth, which rarely happens. When we have a criteria meeting supermoon, the moon can appear as much as 14% larger and 30% brighter than a normal full moon.
Why The Term Supermoon?
No one seems to know the exact origin of the term however, it became popular in March 2011, when the moon’s perigee brought it to less than 221,600 miles from earth; one of the closest full moons in decades.
Then, someone decided that anytime a full moon that coincides with perigee should always be called a “supermoon.” But the Farmers’ Almanac staff doesn’t like to water down the term, and believe that a full moon is truly a supermoon when the full phase and perigee occur at approximately the same time, and the distance is very close; what is usually referred to as an “extreme perigean” supermoon.
The Last Two Supermoons
The last two full Moons — December 3, 2017, and January 1, 2018, — earned their supermoon status because the moment each Moon reached its full phase and when it was at perigee was less than 24 hours apart. You also have to consider the distance to Earth on these occasions:
December 2017
3rd: The moon was astronomically full at 10:47 a.m. EST
4th: The moon was at perigee at 3:53 a.m. EST
The difference in time between the full moon and perigee was 17 hours 6 minutes.
At perigee, the Moon’s distance was 222,132 miles from Earth
January 2018
1st: Moon was at perigee at 4:56 p.m. EST.
1st: The moon was astronomically full at 9:24 p.m. EST.
The difference in time between perigee and the full Moon is 4 hours 28 minutes.
At perigee, the moon’s distance was 221,560 miles from Earth.
This was considered an “extreme perigean supermoon” because the moon was only 131 miles farther out than the closest the moon can ever get, and perigee occurred only 4 hours and 28 minutes prior to the moon being 100% full.W
Here’s a look at these same parameters for the full moon on January 31st:
30th: Moon is at perigee at 5:05 a.m. EST.
31st: The moon is astronomically full at 8:27 a.m. EST.
The difference in time between when perigee occurs and the Moon reaches its 100% full phase is 1 day, 3 hours, 22 minutes.
At perigee, the moon’s distance will be 223,074 miles from Earth.
While the January 31st full Moon will be close, it won’t be as close as the prior two full Moons. In fact, the moment it reaches its 100% full phase at 8:27 a.m, EST, it will be even farther away — 223,816 miles from Earth! Still, there are some who want to stretch the “supermoon” moniker out to include the January 31st full Moon as well.
Supermoon or No, This Full Moon Will Be Totally Eclipsed!
Whatever you call it, the full moon on January 31 brings with it a total lunar eclipse, so it will be quite a show. It will also have another funny moniker attached to it: it’s considered a “Blue Moon” because it’s the second full moon in the month, and some may refer to it as a Blood Moon. This term refers to when the Moon moves into total eclipse it usually appears to light up like a red or coppery ball at and near the total phase of the eclipse (read more about blood moons here.)
Whatever you call it, if you have a clear sky, get out and enjoy it because next month there won’t be any full moon (which is the Farmers’ Almanac explains in both the print edition and online).
Source: Farmers’ Almanac
Image Credit: NASA