Wednesday, 26 June 2013
supermoon
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supermoon
A supermoon is the coincidence of a full moon or a new
moon with the
closest approach the Moon makes to the Earth on its elliptical orbit, resulting
in the largest apparent size of the lunar disk as seen from Earth. The
technical name is the perigee-syzygy of the Earth-Moon-Sun system. The
term "supermoon" is not astronomical,
but originated in modernastrology.[1] The association of the Moon with both oceanic
and crustal tides has led to claims that the supermoon observable fact may be
associated with increased risk of events such as earthquakes and volcanic
eruptions, but the evidence of such a link is widely held to be weak. [2]
The most
recent occurrence was on June 23, 2013, as the closest and prime full moon of the
year and the Moon’s closest encounter with Earth for all of 2013. It will not
be so close again until August 10, 2014.[3]
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Definition[edit]
The
Moon's distance varies each month between approximately 357,000 kilometers
(222,000 mi) and 406,000 km (252,000 mi) due to its elliptical orbit around the Earth(distances given are
center-to-center).[4][5][6]
According
to NASA, a full moon at perigee is up to 14% larger and 30% brighter than one
at its farthest point, or apogee. The full Moon occurring less than one hour
away from perigee is a near-perfect coincidence that happens only every 18
years or so.[7]
Terminology[edit]
...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.[8]
The term supermoon is not used within the astronomical
community, which use the term perigee-syzygy or perigee moon.[9] Perigee is the point at which the Moon is
closest in its orbit to the Earth, and syzygy is a full or new
moon, when the Earth, the Moon and the Sun are united Hence, a
supermoon can be regarded as a combination of the two, although they do not
perfectly coincide each time. On average, about once a year the moon becomes
full within a few hours of perigee.[9]
Effect
on tides[edit]
The
combined effect of the Sun and Moon on the Earth's oceans, the tide,[10] is greatestwhen the Moon is either new or full.[11] At lunar perigee the tidal force is somewhat
stronger,[12] resulting in perigean spring
tides. But even at its most powerful this force be still relatively
weak[5] causing tidal differences of inches at most.[13]
As the tidal force follows an inverse-cube law,
that force is 18% greater than average. However, because the actual amplitude of tidesvaries around the world,
this may not translate into a direct effect.
It has
been claimed that the supermoon of March 19, 2011 was responsible for the
grounding of five ships in the Solent in the UK,[14]but such claims are not support by
scientific evidence.
Natural disasters[edit]
Certain
prognosticators have moved the
goalposts to within
1 or 2 weeks of a supermoon to suggest a causal relationship with specific
natural disasters such as the 2011 Tōhoku
earthquake and tsunami and the 2004
Indian Ocean earthquake and tsunami.[15][16]However
in both cases the Moon was actually farther from the Earth than average.[5] No proof has been found of any correlation
with major earthquakes.[17][18][19]
References[edit]
4.
^ Meeus, Jean (1997). Mathematical
Astronomy Morsels. Richmond, Virginia:
Willmann-Bell. p. 15. ISBN 0-943396-51-4.
5.
^ a b c Plait,
Phil (March 11, 2011). "No, the 'supermoon' didn't cause the
Japanese earthquake". Discover
Magazine.
Retrieved 14 March 2011.
6.
^ Hawley,
John. "Appearance of the Moon Size". Ask a
Scientist. Newton. Retrieved 14 March 2011; no publication date.
7.
^ Phillips,
Tony, Dr. (March 16, 2011). "Super Full Moon".Science@NASA
Headline News. NASA. Archived from the original on May 7, 2012. Retrieved 22 June 2013.
8.
^ Nolle,
Richard. "Supermoon". Astropro. Retrieved 14 March 2011; no publication date; modified March 10,
2011.
9.
^ a b Phillips,
Tony (May 2, 2012). "Perigee "Super Moon" On May
5-6". NASA Science News. NASA. Retrieved 6 May 2012.
10.
^ Plait,
Phil (2008). "Tides, the Earth, the Moon, and why our
days are getting longer". Bad
Astronomy.
Retrieved 14 March 2011; modified March 5, 2011.
11.
^ Sumich,
J.L. (1996). "Animation of spring and neap tides".
NOAA's National Ocean
Service.
Retrieved June 22, 2013.
12.
^ "Apogee and Perigee of the Moon". Moon
Connection.
Retrieved 14 March 2011; no publication date.
14.
^ Andy
Bloxham (March 21, 2011). "Supermoon blamed for stranding five
ships in Solent". Telegraph.co.uk. Retrieved June 22, 2013.
15.
^ Paquette,
Mark (March 1, 2011). "Extreme Super (Full) Moon to Cause
Chaos?". Astronomy Weather Blog.
AccuWeather.
Retrieved 14 March 2011;.
16.
^ "Is the Japanese earthquake the latest
natural disaster to have been caused by a supermoon?". The Daily
Mail. March 11, 2011. Retrieved 14 March 2011.
17.
^ "Can the position of the Moon affect
seismicity?". The Berkeley Seismological Laboratory. 1999. Retrieved 14 March 2011.
18.
^ Fuis,
Gary. "Can the position of the moon or the
planets affect seismicity?". U.S. Geological Survey: Earthquake
Hazards Program.
Retrieved 14 March 2011; no publication date.
19.
^ Wolchover,
Natalie (March 9, 2011). "Will the March 19 "SuperMoon"
Trigger Natural Disasters?". Life's Little Mysteries. Retri
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