Lunar eclipse

[2][3] When the Moon is totally eclipsed by the Earth (a "deep eclipse"),[4][5] it takes on a reddish color that is caused by the planet when it completely blocks direct sunlight from reaching the Moon's surface, as the only light that is reflected from the lunar surface is what has been refracted by the Earth's atmosphere.

However, since the Sun's diameter appears to be about one-quarter of Earth's in the lunar sky, the planet only partially blocks direct sunlight within the penumbra, the outer portion of the shadow.

Total penumbral eclipses are rare, and when these occur, the portion of the Moon closest to the umbra may appear slightly darker than the rest of the lunar disk.

[9] When the Moon's near side entirely passes into the Earth's umbral shadow, a total lunar eclipse occurs.

The moment the Moon enters a complete eclipse, the entire surface will become more or less uniformly bright, being able to reveal stars surrounding it.

It will be true of any planetary body with little or no atmosphere and an irregular cratered surface (e.g., Mercury) when viewed opposite the Sun.

[16] The reddish coloration arises because sunlight reaching the Moon must pass through a long and dense layer of Earth's atmosphere, where it is scattered.

An alternative way of conceiving this scenario is to realize that, as viewed from the Moon, the Sun would appear to be setting (or rising) behind Earth.

[citation needed] Some societies thought it was a demon swallowing the Moon, and that they could chase it away by throwing stones and curses at it.

[17] The Ancient Greeks correctly believed the Earth was round and used the shadow from the lunar eclipse as evidence.

[20] In some Chinese cultures, people would ring bells to prevent a dragon or other wild animals from biting the Moon.

[22] During the Zhou Dynasty (c. 1046–256 BC) in the Book of Songs, the sight of a Red Moon engulfed in darkness was believed to foreshadow famine or disease.

[23] Certain lunar eclipses have been referred to as "blood moons" in popular articles but this is not a scientifically recognized term.

The meaning usually relates to the reddish color a totally eclipsed Moon takes on to observers on Earth.

[25] As sunlight penetrates the atmosphere of Earth, the gaseous layer filters and refracts the rays in such a way that the green to violet wavelengths on the visible spectrum scatter more strongly than the red, thus giving the Moon a reddish cast.

A total lunar eclipse
Composite image of the April 2014 total lunar eclipse from Charleston, West Virginia , United States
A schematic diagram of the shadow cast by Earth . Within the umbra , the central region, the planet totally shields direct sunlight . In contrast, within the penumbra , the outer portion, the sunlight is only partially blocked. (Neither the Sun , Moon , and Earth sizes nor the distances between the bodies are to scale.)
Latter phases of the partial lunar eclipse on 17 July 2019 taken from Gloucestershire , United Kingdom
Timelapse of the total lunar eclipse on 4 March 2007.
October 2014 lunar eclipse viewed from Minneapolis during sunrise on 8 October 2014. Both the Moon and Sun were visible at that time. [ 12 ]
Contact points relative to the Earth's umbral and penumbral shadows, here with the Moon near is descending node
The Moon does not completely darken as it passes through the umbra because Earth's atmosphere refracts sunlight into the shadow cone.
In a lunar eclipse, the Moon often passes through two regions of Earth's shadow : an outer penumbra, where direct sunlight is dimmed, and an inner umbra, where indirect and much dimmer sunlight refracted by Earth's atmosphere shines on the Moon, leaving a reddish color. This can be seen in different exposures of a partial lunar eclipse, for example here with exposures of 1/80, 2/5, and 2 seconds.
Christopher Columbus predicting a lunar eclipse
Totality during the lunar eclipse of 15 May 2022 . Direct sunlight is being blocked by the Earth , and the only light reaching it is sunlight refracted by Earth's atmosphere, producing a reddish color.
As the Earth revolves around the Sun, approximate axial parallelism of the Moon's orbital plane ( tilted five degrees to the Earth's orbital plane ) results in the revolution of the lunar nodes relative to the Earth. This causes an eclipse season approximately every six months, in which a solar eclipse can occur at the new moon phase and a lunar eclipse can occur at the full moon phase.
A painting by Lucien Rudaux showing how a solar eclipse might appear when viewed from the lunar surface. The Moon's surface appears red because the only sunlight available is refracted through Earth's atmosphere on the edges of Earth, as shown in the sky in this painting.