According to Live Science, Sunday's supermoon will reach its peak fullness at 7:32 a.m. EDT. EarthKy.org gives the time of peak fullness at different US time zones: 7:32 a.m. EDT, 6:32 a.m. CDT, 5:32 a.m. MDT and 4:32 a.m. PDT.
A supermoon is the coincidence of a full moon with the closest approach of the Moon to Earth on its elliptic orbit. The incident results in a relatively large apparent size of the Moon's disk as seen by observers on Earth.
Precisely, it is the full moon observed within 12 hours of the lunar perigee, that is, the point in the Moon's elliptic orbit which brings it closest to the Earth. At its closest approach to the Earth (perigee), the Moon is at a distance of about 225,622 miles or 363,104 kilometers, and 252,088 miles or 405, 696 kilometers from the Earth at its farthest, or apogee.
Sunday's supermoon will be the largest this year because it will fall closer to the time of the perigee than any other this year. According to EarthSky.com, the crest of Sunday's lunar full phase, and perigee, will fall within an hour of each other, about 22 minutes precisely.
A full moon will not come as close to the Earth as Sunday's until August 10, 2014. Another supermoon will be seen in July but will not be as close to Earth.
The term supermoon was not coined by astronomers but by an astrologer Richarch Nolle, who defined it 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."
You appreciate why people prefer the astrologer's term "supermoon" when you learn that astronomers call a "supermoon" the perigee-syzygy of the Earth-Moon-Sun system.
The full moon observed at the Moon's closest approach (perigee) to Earth is 14 percent larger and 30 percent brighter than the full moon observed when the Moon is at its farthest point from Earth (apogee).
The distance between the Earth and the Moon varies because the Moon traces an elliptic orbital path around the Earth. An ellipse is a circle drawn out at opposite ends into an oval or "egg" shape. An elliptic orbit is defined technically as a Kepler orbit with eccentricity greater than zero and less than 1, where a "perfectly" circular orbit has an eccentricity of zero.
Sunday's supermoon will come two days after the summer solstice (Friday, June 21, 1:04 a.m. EDT), the longest day of the year in which the Sun reaches its farthest point north of the equator, marking the official beginning of summer in the Northern Hemisphere.
According to the Old Farmer's Almanac, North American farmers, following the tradition of native Algonquin tribes, refer to the full moon observed in June as the Full Strawberry Moon because June is the strawberry-harvesting season in the North America. In Europe it is known as the Full Rose Moon.
Although folklore links the supermoon with natural disasters such earthquakes and floods, scientists have found no evidence of a link between the full moon or supermoon and natural disasters such as Japan's earthquake and tsunami in 2011, and the sinking of the Titanic. According to scientists, the changes in gravitational attraction between the Earth and the Moon at lunar perigee is not enough to induce tectonic forces that could cause earthquakes, floods and tsunamis. However, people living along a coastline are advised to watch for higher-than-usual tides during the perigee.
Live Science reports that John Bellini, geophysicist at the US Geological Survey, said: "A lot of studies have been done on this kind of thing by USGS scientists and others. They haven't found anything significant at all."
The supposed link between human mental health and the supermoon is even more baffling from the scientist perspective of analysis of cause and effect. Live Science reports that a 1985 review of research published in the journal Psychological Bulletin, and a study in 2010, found no evidence (as expected!) that people tend to go "loony" during a supermoon. The study found no evidence of increased incidence of mental hospital admissions, homicides and crimes.
The traditional association of the supermoon with fertility has no scientific grounds, either. It appears that traditional cultures link full moons with fertility because of the coincidence of the cycle with the female menstrual cycle and the sickle shape of the waxing crescent which resembles the appearance of a developing fetus during pregnancy.