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Thread: April 7 SuperMoon NOT 2020 Brightest Moon

  1. #1
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    Cool April 7 SuperMoon NOT 2020 Brightest Moon

    Some in the media are already touting the upcoming Full Moon of 2020 APR 07 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.

    SuperMoons.JPG

    BrightMoons.JPG
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  2. #2
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    Good catch. Most of our fellow citizens simply are unaware of just how sharply peaked that retro-reflective characteristic is in those last few degrees approaching a true opposition.

  3. #3
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    Quote Originally Posted by Hornblower View Post
    Good catch. Most of our fellow citizens simply are unaware of just how sharply peaked that retro-reflective characteristic is in those last few degrees approaching a true opposition.
    Thanks. Indeed, few are aware of the influence of the oppositional flash. It would surprise many to learn that a Full Moon is typically eight times brighter than a Half Moon.

    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.)

    Moon-Orbit.JPG
    Last edited by Centaur; 2020-Apr-08 at 06:56 PM.
    For astronomical graphics and data visit
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  4. #4
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    I am seeing it in all of its glory through breaks in the clouds. Of course I cannot see any perceptible difference between this one and the full Moon a month ago. It would be an interesting experiment to generate test images of exact size and brightness side by side in a laboratory, and find out how much difference there needs to be before observers can see the difference with any certainty.

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