Skip to comments.APOD: Lunations (09/12/18)
Posted on 09/28/2018 9:56:51 AM PDT by zeugma
Our Moon's appearance changes nightly. As the Moon orbits the Earth, the half illuminated by the Sun first becomes increasingly visible, then decreasingly visible. The featured video animates images taken by NASA's Moon-orbiting Lunar Reconnaissance Orbiter to show all 12 lunations that appear this year, 2018. A single lunation describes one full cycle of our Moon, including all of its phases. A full lunation takes about 29.5 days, just under a month (moon-th). As each lunation progresses, sunlight reflects from the Moon at different angles, and so illuminates different features differently. During all of this, of course, the Moon always keeps the same face toward the Earth. What is less apparent night-to-night is that the Moon's apparent size changes slightly, and that a slight wobble called a libration occurs as the Moon progresses along its elliptical orbit.
This is one of the coolest astronomy vids I've ever seen. The amount of information in it is really astounding, and offers a lot of insight into the dynamics of the Earth-Moon system. It's not immediately obvious what all is being displayed besides the obvious moon phases of the lunation, so I'm going to offer a little bit of description of what all is provided.
In the upper left quadrant, is a diagram of the Earth-Moon system orbital path. (Not to scale) If you watch it closely, you'll see that the path taken by the moon doesn't actually repeat. It's more like a spirograph path if you were to draw it out. You can also see that the moon's orbit is a bit elliptical, which means sometimes it is closer, or further away from the earth in its orbit.
There is a line that runs horizontally through the center that also shows a visualization of the varying distance between the earth and moon from a slightly different perspective.
In the lower left quadrant, you'll see the axial tilt of the moon as it goes through its cycle. There is quite a bit more variation there than I expected.
The lower right quadrant shows a bunch of numeric data indicating time, phase, inclination and distance.
There's a lot going on, and it's fairly hypnotic IMO. Hope y'all enjoy it as much as I did.
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