Why Does The Harvest Moon Look So Big?

By Terry Eliasen, Meteorologist, WBZ-TV Exec. Weather Producer

BOSTON (CBS) – The harvest moon is perhaps the most widely known and celebrated of all the full moons, certainly featured in a few famous tunes!

It’s history is deeply rooted in the days before artificial light. The glowing harvest moon would light the countryside at night and help farmers gather their crops before the long winter.

It is also a true signal of changing seasons. The harvest moon is always the closest full moon to the autumnal equinox (this year they are just 6 days apart).

WHY DOES IT LOOK BIGGER?

You may have noticed Thursday night, or in past years, that the harvest moon for some reason appears more dramatic, more vibrant, perhaps even larger.  Well there is some science to back this up!

Typically, the moon rises about 50 minutes later each day/night, but the harvest moon actually rises only about 30 minutes later during the days right before and right after the official full moon. This occurs because the ecliptic path of the moon is making a more narrow angle with the evening horizon around this time of year. So, this means several nights in a row of dramatic moon rises right around the time of sunset.

While it may look bigger, this is simply an optical illusion, sometimes referred to as the “Moon Illusion.” This is a very complex phenomenon, actually debated By many scientists. Wanna know more? I would suggest a Google search – enjoy!

WHAT ABOUT THE ORANGE GLOW?

The orange glow of the moon does actually have a simple explanation. Since the moon is rising near the horizon, you are looking through a lot more atmosphere than if you were looking overhead. More atmosphere means more blue light scattered and more red light is able to emerge.

Finally, you may have heard rumors of a lunar eclipse Friday night. Unfortunately, this show will not be for us in North America. Folks in parts of Africa, Europe and Asia will be treated to a penumbral eclipse, essentially a dimming of the moon, not a full disappearing act.

So crank up the tunes, grab your favorite pumpkin beverage and enjoy the show tonight! The harvest moon will be rising above the countryside at 6:59 p.m.

Follow Terry on Twitter @TerryWBZ

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