Supermoon

In astrology, a supermoon is a full or new moon that coincides with a close approach by the Moon to the Earth. The Moon's distance varies each month between approximately 354,000 km (220,000 mi) and 410,000 km (254,000 mi) due to its elliptical orbit around Earth.

Definition

The name SuperMoon was coined by astrologer Richard Nolle in 1979, defined as:

...a new or full moon which occurs with the Moon at or near (within 90% of) its closest approach to Earth in a given orbit (perigee). In short, Earth, Moon and Sun are all in a line, with Moon in its nearest approach to Earth.

(The phrasing "within 90% of its closest approach" is unclear, but an example on Nolle's website shows that he means that the Earth-Moon distance is in the lowest tenth of its range.)

The term supermoon is not widely accepted or used within the astronomy or scientific community, who prefer the term perigee-syzygy. Perigee is the point at which the moon is closest in its orbit to the Earth, and syzygy is full or new moon, when the Earth, the moon and the sun are aligned. Hence, supermoon can be regarded as a combination of the two, although they do not perfectly coincide each time.

Effect on tides

The combined effect of the Sun and Moon on the Earth's oceans, the tide, is greatest when the Moon is new or full (see Tide#Range variation: springs and neaps). At lunar perigee the tidal force is even stronger, resulting in more extreme high and low tides, but even at its most powerful this force is still considerably weak.

Link to natural disasters

Speculations of a link between the occurrence of supermoons and natural disasters such as earthquakes and tsunami are extremely substantial. Arguments have been made that natural disasters coinciding with years in which supermoons occurred were influenced by the Moon's increased gravitational strength, though because of the monthly alternation between lunar apogee and perigee such an argument cannot be supported unless the disaster in question falls on the actual date of the supermoon.

It has been argued that the Indian Ocean tsunami and earthquake on December 26, 2004, was influenced by a supermoon which occurred 2 weeks later on January 10, 2005. However two weeks before a supermoon the Moon is at the opposite point in its orbit: its apogee (greatest distance). Thus a supermoon effect is impossible.

Most recently, astrologers argued that the Tōhoku earthquake and tsunami that hit Japan on March 11, 2011, was influenced by the March 19 supermoon, the closest supermoon since 1992. The problem with this claim is that on March 11 the Moon was actually closer to apogee than perigee, at approximately 400,000 km (240,000 mi) from the Earth, which is further than the average distance between the Moon and the Earth throughout the Moon's orbital cycle.

While some studies have reported a weak correlation between shallow, very low intensity earthquakes and lunar activity, there is no empirical evidence of any correlation with major earthquakes. Looking at data from 1900 to the present date, calculations have shown that large-scale earthquakes of 8.0 magnitude have not occurred with a greater frequency within 3 days, 1 week, or 2 weeks of supermoons than we would expect by pure chance.

Dates of supermoons between 1950 and 2050

A NASA image of the perigee moon of March 19, 2011 over Washington D.C. near the Lincoln Memorial.

There are approximately four to six supermoons annually. The following is a list of past and predicted extreme supermoons.

• November 10, 1954
• November 20, 1972
• January 8, 1974
• February 26, 1975
• December 2, 1990
• January 19, 1992
• March 8, 1993
• January 10, 2005
• December 12, 2008
• January 30, 2010
• March 19, 2011
• November 14, 2016
• January 2, 2018
• January 21, 2023
• November 25, 2034
• January 13, 2036