For the fourth month in a row, we will see a supermoon on the night from Thursday to Friday. It is also the last one this year. A supermoon is a full moon that appears 14 percent larger and 30 percent brighter than normal because the moon is very close to Earth. But according to the term’s creator, we already had the last supermoon of 2022 last month and it doesn’t count.
The full moon will be Friday, August 12, and at 3:36 a.m. our time, it will be 361,409 km from Earth. That is relatively close, but there is debate whether it is close enough to speak of a supermoon. American astrologer Richard Nolle coined the term supermoon in 1979 and defined the phenomenon as follows: “A new or full moon that occurs during its closest (or within 90 percent of its closest) approach to Earth in a particular orbit (perigee) . In short, the Earth, the Moon, and the Sun are all aligned, with the Moon closest to Earth.” In other words, a supermoon occurs when a new or full moon coincides — or nearly, within 90 percent — with the moment the moon is closest to Earth. At each new or full moon, the Earth, Moon, and Sun are aligned.
Problem is, Nolle didn’t further specify that “certain job” nor explain why he chose 90 percent as the margin. Because of this ambiguity, astronomers often base their determination of supermoons on data from American astrophysicist Fred Espenak, who worked for NASA for more than 30 years and is also known for his predictions of eclipses. Fred Espenak compiled lists of perigee, apogee and lunar phases to define future supermoons. The perigee is the closest point the moon reaches in one complete revolution around the Earth. The apogee is the farthest point from the moon. Perigees and apogees exist because the moon’s orbit around the sun is not a perfect circle, but an ellipse (oval), so the distance of the moon from the earth is not always the same. The average perigee distance is about 363,000 km from Earth, the average apogee distance is about 405,500 km.
On Thursday night, the full moon will not be on perigee, but it will be on at least 90 percent of it, calculated according to the perigee and apogee of the August ‘monthly orbit’ and not of the 2022 ‘year orbit’, as Nolle did. Nolle looked at the nearest perigee and the farthest apogee of the year. He took 90 percent of that difference as the basis for measuring the permitted deviation from the perigee. Espenak made his calculations based on the perigee and apogee of the month in question and the distance from the full moon that month. This explains why in Espenak’s tables we find May 16, 2022 and August 12, 2022 as supermoons, while those dates were not retained by Nolle.
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