Supermoon of 29th August 2015
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 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, but the evidence of such a link is widely held to be unconvincing.
The most recent occurrence was on March 20, 2015.
According to NASA, a full moon at perigee is up to 14% larger (in area, or almost 7% larger diameter) and 30% brighter than one at its farthest point, or apogee.
Terminology
The term supermoon is not used within the astronomical community, which use the term perigee-syzygy or perigee full/new moon. Perigee is the point at which the Moon is closest in its orbit to the Earth, and syzygy is when the Earth, the Moon and the Sun are aligned, which happens at every full or new moon. Hence, a supermoon can be regarded as a combination of the two, although they do not perfectly coincide each time.
Frequency
The full moon cycle is the period between alignments of the lunar perigee with the sun and the earth, which is about 13.9443 synodic months (about 411.8 days). Thus approximately every 14th full moon will be a supermoon. However, halfway through the cycle the full moon will be close to apogee, and the new moons immediately before and after can be supermoons. Thus there may be as many as three supermoons per full moon cycle.
The full moon on September 29, 2015, will present the closest supermoon of the year (356,896 kilometers or 221,754 miles). What’s more, this September 29, 2015 full moon will stage a total lunar eclipse, concluding a series of Blood Moon eclipses that started with the total lunar eclipse of April 15, 2014.
wikipedia.com
earthsky.org
Nessun commento:
Posta un commento