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April 7-8 SuperMoon NOT 2020 Brightest Moon

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Posted (edited)

Some in the media are already touting the upcoming Full Moon of 2020 APR 07-08 as being a SuperMoon and therefore the brightest Moon of the year.

Indeed, it will be the closest and widest Full Moon of 2020. But it will NOT be the brightest. Almost invariably popular science writers seem to assume that nearness to Earth is the only factor in determining a Full Moon's brightness. The other two factors are nearness to Sun and nearness to the ecliptic. The latter factor is related to the phase angle and degree of the oppositional flash. That's why a Moon immediately before or after a lunar eclipse is often one of the brightest of the year even if not nearly a SuperMoon. By my calculations, this month's Full Moon will be the fourth brightest Moon of 2020.



Edited by CentaurZ
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There's another piece of misinformation that is ubiquitous in SuperMoon articles. That is the declaration that the varied distances between Earth and Moon are due to the Moon's elliptical orbit. Actually, the Moon's orbit is almost a perfect circle, only slightly elliptical. Both perigee and apogee occur on the orbit's major axis, not minor axis. The distance variance is due to the fact that the orbit is eccentric, i.e. the Earth is not exactly at the center of the Moon's orbit. (In celestial mechanics there is a relationship between ellipticity and eccentricity, but that is irrelevant here.)


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