Thursday, May 03, 2007

Our Constant Moon?

Most of us probably think of the Moon as our constant and reliable companion, always showing a familiar face. Popular lore has us always seeing the same face of the moon, the "bright side," with the dark side forever hidden from earthbound viewers as the moon orbits in lock-step with the Earth's rotation.

But as with much of science, the tricky little details reveal a more interesting picture. Here is a short animation sequence taken by Laurent Laveder in France that is comprised of full moon images captured every (lunar) month for two years, all compressed into 2 seconds of video.

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This video is a fantastic articulation of the fact that the Moon's orbit around Earth is not, in fact, a perfect circle, but rather an ellipse (with about 5% eccentricity) which travels closer and then farther away in turn and changing apparent size in the process. The orbit is tilted slightly with respect to Earth's daily planetary rotation, presenting slightly varying angles, and there is obviously some wobble in the orbital path, which astronomers call libration. In total, we actually see somewhere closer to 59% of the Moon over time rather than what the pedestrian 50% bright-side model would offer.

Keep in mind that this was a two-YEAR project to take and assemble and process all the monthly images.

Click to enlarge 1152 x 768 pixels (212 ko)

Wikipedia has a great page with more details on the orbit of the Moon, and a hat-tip to Spaceweather.com for the links.

1 comment:

Michelle S. said...

Hi Philip,
As much as I stare at the moon- and am constantly aware of its cycles, even keeping moon calendars at my house - I never actually thought about ever seeing a different view of it until that animation you featured...thanks! very interesting