A "blood moon" (Photo: Helen Colyer)On 27th July 2018 the longest total lunar eclipse of the 21st century will begin. As the Moon rises, it will start to fall behind Earth's shadow. Totality, the period when the Moon is completely covered, will last 103 minutes, which makes this eclipse almost the longest lunar eclipse that can ever take place. The entire event, including periods while the Earth's shadow covers only part of the Moon, will last for several hours. During the eclipse, the Moon will turn a deep red colour, becoming a "blood moon". This was once seen as an omen of terrible events.
A diagram of a lunar eclipse (Gary Hincks)A lunar eclipse occurs when the Earth lies directly between the Sun and the Moon. The Earth casts its shadow on the Moon. As the eclipse begins, the Earth's shadow first darkens the Moon slightly. Then the shadow begins to cover more and more of the Moon until it is entirely hidden. During the July 2018 eclipse, the Moon passes through more or less the exact centre of Earth's shadow. This maximizes the time during which the Moon is blocked from the Sun's rays, and is the reason is why this total lunar eclipse will last so long.
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