.by Anura Guruge
>> March 2013 ‘Worm’ Full Moon over
>> Alton — Mar. 30, 2013.
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The deal with a ‘Super Moon’ is that it is close to full (if not at full) and very close to Earth (if not at its closest).
Obviously we get a full moon each month, or to be precise each Lunar Month which is 27.322 days — rounded up to the ’28’ days that determine women’s cycles etc. So full moons, especially to Buddhists, are always ‘special’, but are really common or garden.
Being closest to Earth also happens each and every month — without fail. If it didn’t we would all be in a heap of trouble! Nearly all, if not all, solar system objects have non-circular orbits. Rather than circular the orbits that nearly everything falls into is an elliptical orbit — i.e., an elongated orbit. The degree of this elongation is referred to as Orbital Eccentricity, ‘0’ denoting a perfect circle and ‘1’ a parabolic (i.e., football shaped) orbit. Closer to ‘0’, the more circular, closer to ‘1’ the more elongated. Most of the planets have near-circular orbits, though they are not circular. Earth’s eccentricity is 0.0167. Mercury has the most elongated orbit at 0.2056, with Pluto, now a dwarf planet, having one of 0.248. Comets, which originate at the furthest edges of the solar system have very high eccentricity, Comet ISON, C/2012 S1 (ISON), having an eccentricity close to ‘1’!
The Moon’s eccentricity is 0.054906.
Here are some cute diagrams from ‘Google’ that will explain this whole notion of elliptical orbits, perigee and apogee. [When talking of orbits around the Sun the comparable terms used are ‘perihelion’ (closest) and ‘aphelion’ (furthest).
How the orbits of comets, in this case periodics which are NOT as elongated as long-term comets, compare in terms of the gas giants.
The Moon’s distance at perigee (which varies slightly from month to month due to some complicated precession motions) varies between 221,324.4 miles to 230,018.4 miles, the average 225,670 miles.
The apogee, on average, is at 252,088 miles.
So this weekend we get both a full moon and one that is at apogee — these two events happening very close together tomorrow morning between 7:11 am and 7:33 am in the Southern sky (very close to the horizon) over New Hampshire. I will be asleep. It will be quite spectacular tonight too.
But, to be fair we had a Super Moon in May and another one in July — those the in both those cases the perigee was within 90% of closest as opposed to 100%. That is why tomorrow’s is more ‘special’ than most.
On AVERAGE we get 2 to 3 Super Moons each year — keyword here being ‘average’.
This weekend the brightness of the moon, measured per the confusing apparent magnitude scale which goes backwards [i.e., less NEGATIVE the brighter], will be ~ ‘-12.xx’. The maximum brightness of the full moon is -12.92; the average -12.74.
A real picture of the Moon orbiting the Earth taken by NASA robotic spacecraft ‘Deep Impact’, in 2005, from 30 million miles away.