The action begins at 3:16 a.m. PDT on the morning of April 4 when the edge of the moon first enters the amber core of Earth’s shadow. For the next hour and 45 minutes, Earth’s shadow will move across the lunar disk, ultimately covering the entire moon at 4:58 a.m. PDT. The total phase of the lunar eclipse will only last about 5 minutes, making it the shortest lunar eclipse of the century on the morning of Easter Vigil, traditionally observed as the period between Good Friday and Easter Sunday. The eclipse also falls within the first night of Passover, observed by Jews worldwide beginning Friday at sunset. Some total eclipses last for more than an hour, in this case, totality spans just 4 minutes and 43 seconds since the moon will be skimming the outskirts of the Earth’s shadow, rather than passing centrally through it. The moon’s red tint is caused by the Earth covering the sun. This red light from the rim of the Earth then beams onto moon, transforming it into a giant red orb. Lunar eclipses usually come in no particular order, but sometimes the sequence is more orderly. When four lunar eclipses are all total, the series is called a Tetrad. This Saturday will be the third of four total eclipses in the 18-month long tetrad series. Previous eclipses occurred on April 15, 2014 and. Oct. 8, 2014. After Saturday, the next one is expected on Sept. 28, 2015. Such a closely-spaced succession of eclipses is a fairly rare occurrence.