Image credit & copyright: Daniel LaShomb.
It’s been a fun year for supermoons, black and blue moons but the full moon on Monday, November 14, 2016 will be somewhat special as it will be the biggest supermoon since January 26, 1948 and will be the biggest one until November 25, 2034! Something to keep in mind here as you see the data below is that these full moon/perigee times don’t occur at night for many people. That’s not a bad thing because if you can’t see the Moon on the night of the 14th check it out the night before because it will look about the same.
Exact Full Moon Time: 08:53 EST (13:53 UTC).
Exact Perigee Time: 06:24 EST (11:24 UTC) at a distance of 356,511 km (221,525 mi.).
Angular (apparent) Size: (how large the moon will look on the sky): 33’30” arcminutes. Average angular size for the full moon is about 30’ arcminutes.
What is a supermoon?:
Simply stated, a supermoon is a full or new moon that occurs within 90% of perigee (Moon’s closest point to Earth in its orbit).
Are they really bigger?:
No! It all comes down to apparent size or, how it looks on the sky. As far as the actual Moon, it’s still its usual 2,159 mi. (3,474.5 km) diameter self. So how does the Moon appear to be different sizes at different times? Orbital mechanics. We tend to draw orbits in circles and they’re usually not too far off but the truth is, they’re slightly elliptical (oval) which means sometimes the Moon is closer to Earth than it is at other times. When the Moon is at its closest point, it’s called perigee. When the Moon is at its furthest point from Earth it’s called apogee. The “gee” in these words is for geo or Earth while “peri” is near and ‘apo’ is far (all Greek). The words apogee and perigee are actually French with Greek origins.
As you can see from the distances below, the Moon from perigee to apogee is only about a 10% change so like I said above, the orbit isn’t a perfect circle but it’s really not too far off. That 10% distance change makes supermoons about 14% larger and 30% brighter than their micromoon (apogee full moon) counterparts. That sure does sound like a lot (and it is) but it’s really difficult to notice the difference. Even those of us who view the moon all month long for its different phases and features have a hard time distinguishing the difference in apparent (angular) size and associated brightness.
Moon’s average distance from Earth is 238,900 mi. (384,472 km.)
Moon’s average perigee (close): 225,804 mi (363,396 km).
Moon’s average apogee (far): 251,968 mi. (405,504 km).
What effect will it have?:
Not much really. You may notice larger than normal tides but even then were not talking about much. If you live in a low lying costal area you may notice a difference of a few feet, maximum.
Where did the name “supermoon” come from?:
Historically (and still today) astronomers call a full or new moon that lands on the night of perigee a perigee or proxigean full or new moon, though due to the title supermoon catching on many are running with that name as it’s a pretty cool name and the parameters that it works within allow for about 4-6 per year. The term supermoon comes not from science but from astrology; more specifically, astrologer Richard Nolle who coined the phrase and set guidelines that state any NEW or FULL Moon within 90% of perigee is a supermoon. So there you go, it’s not a big deal but either way it’s encouraging people who otherwise wouldn’t be looking up to do so and that is certainly a good thing in my opinion. If you have questions, as always please ask.