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, or perigee, leading to the technical name for a supermoon of the perigee-syzygy of the Earth-Moon-Sun system. The association of the Moon with both oceanic and crustal tides has led to claims that the supermoon phenomenon may be associated with increased risk of events such as earthquakes and volcanic eruptions. However, the evidence of such a link is widely held to be unconvincing.
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).
The size and brightness of an object follows an inverse-square law, which means that a full moon at perigee is 12% larger and brighter than an average full moon. However, because the offset of the moon’s orbit versus its phases is only two days, this change in appearance is gradual from month to month and therefore is not usually noticeable to a casual observer.
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 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 a full or new moon, when the Earth, the Moon and the Sun are aligned. Hence, a supermoon can be regarded as a combination of the two, although they do not perfectly coincide each time. Syzygy may occur within a maximum of 12 hours from perigee during a supermoon, and 1 hour from perigee during an extreme supermoon. [Source: Wikipedia]
SPACE.com UPDATE: For the latest on Saturday’s “supermoon” and meteor shower, read our latest story here:‘Supermoon’ Science: Why Saturday’s Full Moon is Biggest of 2012
Skywatchers take note: The biggest full moon of the year is due to arrive this weekend.
The moon will officially become full Saturday (May 5) at 11:35 p.m. EDT. And because this month’s full moon coincides with the moon’s perigee — its closest approach to Earth — it will also be the year’s biggest.
The moon will swing in 221,802 miles (356,955 kilometers) from our planet, offering skywatchers a spectacular view of an extra-big, extra-bright moon, nicknamed a supermoon.
BUSINESS INSIDER: Although the moon officially becomes full at 11:35 p.m. — just one minute after reaching lunar perigee —the best viewing time will be in the early evening, shortly after sunset when the moon is near the horizon, according to National Geographic’s Andrew Fazekas.
“What you should see is the moon rising, deeply colored and looming over the foreground objects,” Geza Gyuk, an astronomer at the Adler Planetarium in Chicago, told Fazekas.
There’s also no need to freak out that the moon’s close proximity to Earth will trigger earthquakes and volcanic eruptions. While a supermoon does bring extra-high tides, “it should not affect the internal energy balance of the Earth since there are lunar tides every day,” says Dr. James Garvin, chief scientist at NASA’s Goddard Space Flight Center.
In other words, the extra gravitational force isn’t big enough to produce any significant changes in seismic activity. So, just enjoy the show.
NASA: Another “supermoon” is in the offing. The perigee full moon on May 5, 2012 will be as much as 14 percent bigger and 30 percent brighter than other full moons of 2012.