Waning Gibbous Moon

Image Credit: Adam Brown

I caught this image of the waning gibbous moon the other night (Be sure to click on the image to see a larger version). Amazing, isn't it? I've always loved the moon. Not just because it's a beautiful object in our sky, but because I'm convinced there are mysteries there to discover.

The moon in this photo is in the "waning gibbous" phase. This means that the moon is less than full and moving toward a new moon (when we can only see the night side). In other words, we can see more than half (but less than all) of the daylight side of the moon and we'll be seeing more of the night side of the moon in the coming days until only half of the daylight side is visible. This will be the quarter moon.

Here's a tip for remembering the phases of the moon: In the Northern Hemisphere, the right side of the moon is the one that will appear to "grow." In the image above, the ride side is dark, so the moon is moving away from full and the dark part is turning toward us. This tells us that the light part is "shrinking" (it's really not, it's just that we can't see as much of it.) That's the "waning" part.

Waning=shrinking

The moon is a little more than half lit, which is called "gibbous." Gibbous comes from a word that means chubby or pot-bellied. Because the light side is "shrinking," that pot-belly part will become smaller until the moon is in Quarter phase where we can see only half of the day side.

The moon is an excellent target for a backyard telescope or even a good pair of binoculars.

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