Just as solar eclipses always happen at the new moon, lunar eclipses always happen at the full moon. During a lunar eclipse, the moon passes directly behind the Earth into its shadow (called the umbra). This can only happen during a full moon because the Earth, Sun and Moon must be aligned exactly.
The full moon almost always appears with a coppery shade of red during a total lunar eclipse because of the sunlight that is filtered and refracted by the Earth’s atmosphere. (The only time it wouldn’t look red is when pronounced volcanic activity might make the moon’s face appear more brownish or gray in color).
During a lunar eclipse, Earth’s shadow is visible creeping across the moon’s face, and this shadow will grow until it completely covers the moon. Then at totality, when the moon is fully covered by the Earth’s shadow, the blood red tinge will appear. This short NASA video does a phenomenal job describing why the moon turns red during an eclipse.
What makes Saturday’s blood moon so significant from a religious prophecy perspective is that it is part of a rare series of four full lunar eclipses each spaced out six months apart, known as a lunar tetrad…all falling on Jewish holidays!
Lunar eclipses can often last hours, while solar eclipses usually only last a few short minutes. During some lunar eclipses, totality (where the moon is completely covered by Earth’s shadow) can last up to an hour. However, Saturday’s lunar eclipse is the shortest of the entire century according to NASA, with totality lasting only 4 minutes and 43 seconds!
Source : themindunleashed.org