Explain xkcd: It's 'cause you're dumb.
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Title text: Whenever I see a picture of the moon where the points go more than halfway around, I assume it's being eclipsed by one of those Independence Day ships and interpret the rest of the image in light of that.
|| This explanation may be incomplete or incorrect: Table needs pictures.|
The phases of the moon are created by sunlight reflecting off the moon's surface. This means that the bright side of the moon always needs to be facing towards the sun. However, the moon often appears in works of art in ways that are very dramatic, but violate this rule. This comic lists some of the some common mistakes. In some cases, a depiction may be unrealistic in multiple ways - for example, the Flag of Tunisia has both unrealistic horns and a star visible between the horns, while the Charles VI tarot shows a moon with over-long horns pointing towards the horizon.
Explanation of individual items in the list
| Crescent moon with points away from horizon
|Crescent moon with points towards horizon
|| This can only happen when the sun is above the horizon. This isn't necessarily only during a solar eclipse, but since a crescent moon means that the Sun and Moon are relatively close in the sky, it's hard to see at other times.
|| Van Gogh, Landscape with Couple Walking and Crescent Moon
|Crescent-like moon where the black area doesn't touch the poles
|| The moon is a nearly-perfect sphere, so when it's lit from one side, the dark side will always cover precisely 50% of its surface, and the dark area should begin and end on the moon's axis. If the moon looks like this, the shadows are in the wrong place. This is only possible during a partial solar eclipse, the start of an annular eclipse, or if the Earth is casting an extra shadow on the moon, a lunar eclipse. Randall labels the lunar eclipse "dubious", since the shadow during would be much fuzzier than shown here.
|| Van Gogh, Starry Night
| Crescent-like moon where the horns extend well past the poles
|| Again, the shadow should just touch the poles. This situation is even harder to create than the previous one - the Earth's shadow is too big to cover the moon but leave an edge like this - a huge Independence Day spaceship might be the right size. It does however resemble a partial annular eclipse if you imagine that the black area is the moon covering up the white sun.
|| Alcoholic Blues
|Crescent moon blocking stars
|Crescent moon with stars between horns
|| As the moon is a huge ball, it should block the stars behind it. If stars are visible, there is either a hole, or a light-source on the moon. As the Star and Crescent, the image is sometimes considered a symbol of Islam, although it's relatively recent and there's no traditional basis for putting the star between the horns - as originally used on the Flag of Turkey, the star appears in a realistic position.
|| Edwin Blashfield, Spring Scattering Stars
|| This transcript is incomplete. Please help editing it! Thanks.
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