The apparent size of the Moon is determined by its distance from the Earth. Since the natural satellite’s orbit, like most orbits of celestial bodies, has the form of an ellipsis, the distance between Moon and Earth varies by 14% over the course of one lunation (the Moon’s 29-day rotation around the Earth). At 7:35 a.m. GMT today the Moon was almost as far from the Earth as possible – 252,517 miles (406,387 km). This is why tonight’s Full Moon will be the tiniest of 2015.
The orbit of our satellite being elliptical, not only do its phases vary during a lunation, but so does its apparent size (as seen from Earth). When the Moon reaches the perigee (closest point to the Earth in the lunar orbit), its visible size is noticeably bigger than the visible size of the same celestial body at the apogee (furthest point from the Earth in the lunar orbit). The minimum distance reached at the closest lunar perigee is 221,500 miles (356,400 kilometers). The maximum apogee is 252,700 miles (406,700 km), only 313 km (0,077 %) farther than tonight’s Micromoon. The actual apogee occurred this morning, but in the evening the Moon will still be farther from the Earth than in any other month of this year.
To observe the phenomenon from the British Isles, watch out for moonrise a couple of minutes after sunset (the exact time for most of this region is 6:05 p.m. GMT), in the opposite direction from the setting sun. If you are into peculiarities of the Moon, don’t miss this one, because the next smaller Full Moon will be as late as January 27, 2032. Because this apogee is so close to the maximum, the Full Moon (along with the lunar eclipse) of September 28th will be a Supermoon.
For those who wish to be very precise, it must be noted that actual perigee and apogee distances are correctly calculated between the centers of the two celestial spheres, which means we have to deduce nearly 4,000 miles from the 252,387 miles in order to approximate our exact distance from the Moon, because we are located on the surface of the Earth. So don’t worry, the Moon is not that horribly far.
image source: Astronomy Now