Caption: The explication of the reddening of the Moon in a total lunar eclipse.

Features:

1. As light rays travel through the Earth's atmosphere they are progressively reddened by the preferential scattering out of blue light. The out scattering is, of course, the cause of the blue sky.

   Obviously, light rays that beam most directly on the Earth are least reddened and those that traverse the Earth's terminator are most reddened: hence the redness of sunrise and sunset.

2. Thus, the light rays that bend around the Earth due to refraction in traversing the Earth's atmosphere are reddened. Because the change in Earth's atmosphere density is continuous and NOT sharp (as at a matter interface), the refraction happens continuously in passing through the Earth's atmosphere and NOT at a sharply defined layer.

3. The refracted light rays can travel into the Earth's umbra and give the totally eclipsed Moon a reddish hue in light reflected from the Moon to the Earth.

   Recall, NO straight line light rays from the Sun can reach the Moon when it is inside the Earth's umbra.

4. The reddened Moon is sometimes called a blood moon, but this a modern term, NOT a traditional one---in fact, it's a bunch of nonsense.

5. Reddened color of the Moon in a total lunar eclipse depends on the Earth atmospheric conditions at the Earth's terminator: the Earth's day-night line which is also the limb of the Earth as seen from the Moon. These conditions will affect the overall brightness and will cause uneven reddening. If the terminator is very cloudy, there may be NO obvious reddening and the Moon can look quite dim.

   The location of the Moon in the Earth's umbra is another factor: the closer the Moon is the center the dimmer it will be all other things being equal and off the center there is a greater tendency for uneven illumination by the refracted light rays.

6. See Eclipse keywords below (local link / general link: eclipse_keywords.html).
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