What counts as a supermoon
A supermoon is a full moon that happens when the Moon is unusually close to Earth. There is no official definition. We call a full moon a supermoon when the Moon’s distance at that instant is at most 367,607 km: Fred Espenak’s limit, the Moon’s mean perigee distance (363,396 km) plus a tenth of the way to its mean apogee distance (405,504 km). It is Richard Nolle’s original idea (1979) of “within 90% of” closest approach, turned into a distance.
Other sources draw the line elsewhere, for instance at 360,000 km or 358,884 km, which gives shorter lists, so a full moon can be a supermoon on one site and not on another. A supermoon looks at most about 14% wider and 30% brighter than the smallest full moon of the year, a difference that is hard to notice without a comparison.
Two kinds of blue moon
A blue moon is not blue. Today the term usually means the second full moon in a calendar month, which happens roughly every two to three years because a lunar cycle (29.5 days) is shorter than most months. The older rule, from the Maine Farmers’ Almanac, calls the third full moon of an astronomical season with four full moons a blue moon (seasons run from equinox to solstice and back).
We mark both and say which. Months and seasons are counted in UTC: in a time zone far from UTC, a full moon near midnight can fall in a different month, and the blue moon moves to the neighbouring date or disappears there.
Lunar eclipses at full moon
A lunar eclipse happens at a full moon when the Moon passes through the Earth’s shadow, which needs the full moon to be close to the plane of the Earth’s orbit. We compare the Moon’s distance from that plane with the size of the Earth’s shadow at the Moon to tell penumbral, partial and total eclipses apart. Where the eclipse pages list the eclipse, its name links to them for times and local visibility.
Penumbral eclipses are subtle: the Moon only dims slightly and often nothing is visible by eye. Partial and total eclipses are visible from the whole night side of the Earth.
How accurate this is
The phases come from Jean Meeus’s Astronomical Algorithms (chapter 49) and agree with the US Naval Observatory’s tables to the minute for 2026–2027. Equinoxes and solstices follow Meeus chapter 27 and agree with the Observatory within two minutes. The Moon’s distance has an error of a few kilometres, which only matters for a full moon within a few kilometres of the supermoon limit.
The calculations assume a constant difference between Earth time and UTC and are good for 2000–2050; beyond that the minutes drift. The names are folklore, not astronomy.