Thursday, 3 January 2019

Partial Solar Eclipse to be visible from East Asia and parts of Alaska.

A partial Solar Eclipse will occur on Saturday 5-Sunday 6 January 2019, which will be visible from Japan, Korea, eastern China and parts of the Russian Far East. Part of the eclipse will also be visible from northern China, Mongolia, Siberia, and parts of Alaska, where the Sun will either rise or set part way through the eclipse. The event will occur between 23.34 pm on Saturday and 3.48 am on Sunday, GMT.

The area over which the 5-6 January partial Solar Eclipse will be visible. Areas in darker grey will be able to observe the entire eclipse, in the lighter grey areas the eclipse will either begin before sunrise or end after sunset, so only part of the event will be visible. HMNautical Almanac Office.

Eclipses are a product of the way the Earth, Moon and Sun move about one-another. The Moon orbits the Earth every 28 days, while the Earth orbits the Sun every 365 days, and because the two Sun and Moon appear roughly the same size when seen from Earth, it is quite possible for the Moon to block out the light of the Sun. At first sight this would seem likely to happen every month at the New Moon, when the Moon is on the same side of the Earth as the Sun, and therefore invisible (the Moon produced no light of its own, when we see the Moon we are seeing reflected sunlight, but this can only happen when we can see parts of the Moon illuminated by the Sun).

 The relative positions of the Sun, Moon and Earth during a Solar eclipse. Starry Night.

However the Moon does not orbit in quite the same plane as the Earth orbits the Sun, so the Eclipses only occur when the two orbital planes cross one-another; this typically happens two or three times a year, and always at the New Moon. During Total Eclipses the Moon entirely blocks the light of the Sun, however most Eclipses are Partial, the Moon only partially blocks the light of the Sun.

How the differing inclinations of the Earth and Moon's orbits prevent us having an eclipse every 28 days. Starry Skies.

Although the light of the Sun is reduced during an Eclipse, it is still extremely dangerous to look directly at the Sun, and an eclipse should always be viewed using appropriate equipment. 

Animation showing the shadow of the Moon at five minute intervals on 5-6 January 2019. Andrew Sinclair/HM Nautical Almanac.

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