Watch the Full Moon Not Happen


There will be no full moon in February 2018. You can watch this non-event unfold over two weeks by following the motion of the moon in the sky against a non-moving object on earth. The ball on top of a flagpole is a good aid to get a new perspective on moon phases, for during the day the ball phase and moon phase match.

The new moon--when the moon is nearly in front of the sun--happens Thursday, February 15 at 4:05 pm EST. Over the next couple of days the moon will re-emerge in the daytime sky, seeming to move to the left, away from the brilliant sun. In the images of flagpoles, the phases of the moon go from right to left, too.

The waxing crescent moon, seen below the arrow, is hard to find among the wispy daytime clouds. Days later comes the first quarter, when a quarter of a "moonth" has elapsed and the right half of the globes--both moon and flagpole ball--are visibly illuminated. Nearly a week later, shown on the far left, a gibbous moon is noticeably shy of being full.

Watch all you want, you still won't see the moon turn full in February 2018, but it's only because of the artifice of the calendar. In January the moon disappeared during a total lunar eclipse on the last day of the month. Count forward a lunar month (or synodic month), about 29.5 days, until the next full moon and you've completed 28 days of the calendar month before the next full moon happens. That 29.5th day between identical phases--in this case, full moon--happens on the first day of March 2018.

In other words, you need 29.5 days, but the full moon falls outside of February 2018 like two bookends-- on the last day of January and the first day of March. That happens when you're a 28-day month.

For the same reason, you'll never get a blue moon (the second of two full moons in one month) in February. And because of time zone differences, some people can see a specific moon phase on one date while others see the same event on a different date.

A simple animation and description at http://www.sumanasinc.com/webcontent/animations/content/sidereal.html conveys the difference between types of months. Moon phases for your location can be found at https://www.timeanddate.com/moon/phases/. David Chapman describes more about the February 2018 moon phases better than I.

The image below shows the full moon of March 31, 2018. Don't see it? Because the moon was totally eclipsed in the morning twilight, it disappeared from view just before it set over Lake Michigan.

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