Did you see the “Snow Moon” rise this past weekend while you were out hunting for the “green comet?” A stunning sight in clear skies, the monthly rise of the full Moon as its draped in orange hues is one of the highlights of the astronomical month, but there was something rather odd about this one.
It was the smallest full Moon of the year. Why the Moon change size?
Its orbit of Earth is not perfectly round, but elliptical. So in any given month there is a point when its closest to us and therefore appears largest in our sky (perigee), and a point when its farthest, and therefore looks smaller (apogee).
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Perigee and apogee happen every month 14 days apart, but only rarely do they coincide with the phases of the Moon we notice most easily—the full Moon.
In January 21, 2023, the New Moon was the closest it will come to our planet since the year 1030. So it follows that 14 days later the full Moon was particularly far away. Not a century-record-breaker, but the farthest of 2023.
Close and distant full Moons do have names. Scientifically they’re called a perigee and apogee full Moons, respectively, though the more colloquial name for the formers is, of course, a “supermoon.” The latter doesn’t really have a name, though “micromoon” is one option.
The distance of the Moon is important in determining the height of tides, but it’s also critical during “eclipse seasons,” the first of which is coming up soon. Every 173 days, for between 31 and 37 days, the Moon is lined-up perfectly to intersect the ecliptic—the apparent path of the Sun through our daytime sky. It’s literally the plane of Earth’s orbit of the Sun. During an eclipse season two (and sometimes three) solar and lunar eclipses can occur, each one every half-an-orbit.
During an eclipse season a New Moon that’s relatively close to Earth can block out 100% of the Sun’s disk and cause a total solar eclipse. The duration of totality depends on exactly how far away the Moon is from Earth—the closer it is, the wider the Moon’s shadow across Earth and the longer the duration of totality.
However, if the New Moon’ is relatively distant and thus looks smaller, it can’t completely cover the Sun and the the result is an annular solar eclipse (also called a “ring of fire”), which next happens across the US, Mexico and South America on October 14, 2023. During that eclipse the Moon will cover just over 90% of the Sun’s disk.
The next total solar eclipse will occur on April 20, 2023 in Australia, Timor Leste and West Papua. It’s a rather unusual scenario because the Moon is right on the cusp of being too far away. As a result it will just fail to block 100% of the Sun as the Moon’s shadow strikes and leaves Earth, but since the middle of the path is slightly closer to the Moon (simply because Earth is a sphere), a short totality of no more than 76 seconds will be experienced by intrepid eclipse-chasers.
When is the next full Moon? The next full moon—the “Worm Moon”—will occur on Tuesday, March 7, 2023. From Europe there will be a perfect alignment of Moon and Sun. In London the full Moon will rise in the east at precisely the same time as the Sun sets in the west.
The final full Moon of winter in the northern hemisphere, the “Worm Moon” is named for the worms that appear in the soil as the temperatures gradually rise. The name comes from native American tribes, but other cultures have called March’s full Moon the “Lenten Moon,” which means spring Moon.