The Full Moon tonight, on May 5, 2012 at 11:36 PM EDT, occurs a mere 2 minutes after perigee AND this is one of the closest possible perigee distances. The distance between the Moon and Earth at tonight's perigee at 11:34 PM EDT is 221,800 miles. So the reason this is a Super Full Moon is because it is occurring closer than its mean perigee. Occurring at perigee alone is not enough to make it a Super Moon. It must also be closer to Earth than its average perigee distance.
A Super Moon occurs when a Full or New Moon
exceeds its mean perigee distance to Earth. As the moon orbits around Earth on its elliptical path it reaches points of perigee (closest to Earth) and apogee (furthest from Earth). The moon is larger in the sky when at perigee and smaller at apogee. The mean (average) perigee distance between Earth & Moon is around 225,000 miles. However the actual distance at perigee can be between approximately 221,800 - 229,800 miles at perigee.
To give you an idea of the varying distance between Earth & Moon at perigee, and how the cycle of perigee correlates to the lunation cycle, I've created the following list for the year 2012.
Annular Eclipses & Apogee
The mean distance at apogee, when the moon is furthest from Earth and smaller in the sky is about 251,900 miles. The moon is smallest in the sky at apogee.
We have a Solar Eclipse coming up on May 20, 2012 with the New Moon at 7:48 PM EDT. This is the day after the Moon reaches apogee (furthest distance from Earth) on May 19, 2012 at 12:14 PM EDT. Therefore the New Moon will be too small to cover the Sun's disk entirely which produces an Annular Eclipse. A ring of fire will appear around the Moon as it passes in front of the Sun. The orb between the New Moon at tropical 00-Gemini-21and South Node at tropical 05-Gemini-02 falls in the range where a Total Eclipse must occur BUT the moon is too small to totally eclipse the sun. Therefore it is called Annular and leaves a ring of fire. Basically all annular eclipses would be total if the Moon was not near perigee and was larger in the sky.
While we can find historical accounts of eclipses from the writings of ancient poets and storytellers of all cultures, this one from the Ramayana is what I believe to be an account of an annular eclipse - the big halo possibly being what we call a ring of fire today. Rahu is the North Node, so this would be an annular eclipse with the New Moon (Sun & Moon) conjunct the North Node.
In the proximity of the Sun there appeared a dark reddish disc; at an odd hour of the day the evening dusk approached at an extremely fast pace to be followed by a sudden nightfall; nothing could be discerned anymore; the birds and the animals became awestricken and started howling at the top of their voice; the Sun was totally engulfed by Rahu and appeared to be totally dull, but a big halo was seen around the dark disc of the Sun; some stars and planets became visible....
The Nov 13, 2012 Solar Eclipse occurs half a day before apogee (see the above table for Nov 14). The orb between the New Moon (Sun-Moon conj) at tropical 21-Scorpio-57 and the North Node at 26-Scorpio-03 is again within the range where a Total Eclipse must occur. This time with the Moon near perigee, it will be large enough to cover the Sun's disk entirely. In both of these eclipses the orb between New Moon & Node is about 5 degrees. Whether it is total or annular depends on perigee or apogee.
