What is a “Supermoon”?

7 August 2014     

ALERT: FULL SUPERMOON ON SUNDAY 10 AUGUST 2014
ALERT: PERSEIDS METEOR SHOWER PEAKS TUESDAY 12 AUGUST 2014

The Short Answer (TSA)

            It’s a bird!  It’s a plane!  No it’s . . . Super Moon?

            The name Supermoon was first used by Richard Nolle in 1979.  There is a Supermoon whenever the Moon, in its orbit, is closest to the Earth at the time of a New Moon or a Full Moon. 

            During the New Moon phase, none of the Moon’s face is sunlit.  So you won’t see a New “Super” Moon in the sky.  On the other hand, when Full, the Moon is at its biggest and brightest.  And if you are particular about your big, bright Moons, the Full “Super” Moon if for you.  At that time, not only is the Moon Full, but its about as close as the Moon gets to the Earth.  What does this all mean?  The Full “Super” Moon is the largest Full Moon you can see in the sky.

            The Moon follows an “irregular” orbit around the Earth.  In other words, the Moon isn’t always the same distance from the Earth.  When the Moon is closest, the astronomical term is “perigee.”  When the Moon is farthest away, it’s called the term is “apogee.”  If you look at the pictures, below, you’ll understand that there’s a noticeable difference in size between the closest (perigee) and farthest (apogee) Full Moon.

Moon at its farthest away (apogee) & Moon at its closest (perigee)

            Technically, we have a Supermoon whenever there is a Full Moon or a New Moon “near” the time of the closest approach of the Moon to the Earth.  How “near” is “near?”  Near is whenever the Moon within 90% of its closest approach (perigee). 

            Well, percentages are notoriously confusing, so I did some checking.  If you are interested, according to Richard Nolle, it’s good enough to say that whenever (1) there is a New or Full Moon and (2) the Moon is less that 368,630 kilometers or 229,057 miles from the Earth, you’ve got a Supermoon.

            Question: Since you can’t see the Moon during the New Moon phase, why would anyone care whether it’s “bigger?”  In other words, why would anyone bother to call an invisible New Moon a “Supermoon?”  The name “super” seems to be “overselling” the Moon at a time when you can’t even see it.

            Answer: “Supermoon” is not an astronomer’s term.  In astronomy, the Supermoon is called “perigee-syzygy.”  That is, perigee = Moon closet to the earth.  And, syzygy = alignment of the Sun, Moon and Earth.  And to take the meaning of “syzygy” to the next level: the only alignments of the Sun, Moon and Earth are -- you guessed it – when the Moon is New or Full.

            Anyway, with a formal name like “perigee-syzygy” it’s easy to see why the name “Supermoon” caught on.  But where did the term “Supermoon” comes from?  It’s an astrological term, but “astrological” can have two meanings. 

            Sometimes, “astrological” refers to a belief that the position of the Sun, Moon and planets, at the time of a person’s birth, correspond to personal traits of character.   And, comparing the planets positions at birth with, later, planetary movements are thought to mark certain types of later life events. 

            But when professional scientists use the word “astrology” they are sometimes referring (unfavorably) to a theory suggesting that an astronomical event has an effect on the physical Earth.  And that is just what Mr. Nolle was suggesting when he coined the name “Supermoon.”  Mr. Nolle relates the occurrence of earthquakes and volcanic eruptions to alignments of the Sun and Moon in relation to the Earth. 

            At the New Moon, the Sun and Moon are both together exerting a gravitational pull on one side of the Earth.  At the Full Moon the Sun and Moon are on opposite sides of the Earth gravitationally pulling on the Earth from both directions.  If the Moon is New or Full, at the same time that it’s closest to the Earth, (a supermoon), the gravitational pull is even stronger.  So, could Supermoons cause earthquakes?

            The scientific community says no.  There is no evidence that these alignments exert enough gravitational force to affect anything other than the ocean tides.  Mr. Nolle disagrees asserting that if you use his time windows and look for earth movements (earthquakes) of particular magnitudes, Supermoons coincide with certain types of geological events. 

            Mr. Nolle’s own explanation of what he means by a Supermoon appears in the link below.  A complete explanation would change this post from a “short” answer to a “long” answer. 

Supermoon: What It Is, What It Means

M Grossmann of Hazelwood, Missouri
(& Belleville, Illinois)
About the Author
7 August 2014