Sunday 27 September 2015

Eclipse of the Supermoon.

A total Lunar Eclipse will occur on 28 September 2015, starting at about ten minutes past midnight GMT. It will be visible across much of Western Europe and West Africa, as well as Eastern North America, and all of South America and the islands of the Atlantic and Caribean. Part of the eclipse will be visible from remaining areas of North America, Africa and Europe as well as western Asia and many islands in the Pacific and Indian Oceans, although in these areas the Moon will either rise part way through the eclipse, or set before it is complete.

Areas from which the 28 September 2015 Lunar Eclipse will be visible. In the white area the full extent of the eclipse will be visible, in the shaded areas it will either begin before the Moon rises or end after the Moon has set, while in the darkest area it will not be visible at all. HM Nautical Almanac Office.

The Moon produces no light of its own, but 'shines' with reflected light from the Sun. Thus at Full Moon the Moon is on the opposite side of the Earth to the Sun, and its illuminated side is turned towards us, but at New Moon the Moon is between the Earth and the Sun, so that its illuminated side is turned away from us.

Lunar eclipses occur when the Moon passes through the Earth's shadow. This can only happen at Full Moon (unlike Solar Eclipses, which happen only when the Moon passes between the Earth and the Sum, and therefore only occur at New Moon), but does not happen every Lunar Month as the Sun, Moon and Earth are not in a perfect, unwavering line, but rather both the Earth and the Moon wobble slightly as they orbit their parent bodies, rising above and sinking bellow the plane of the ecliptic (the plane upon which they would all be in line every month).

Because the Moon is passing through a shadow, rather than being blocked from our view, it does not completely disappear during an eclipse like the Sun, but rather goes through two distinct phases of dimming, the Penumbra, when it is still partially illuminated by the Sun, and the Umbra, when the Earth completely blocks direct sunlight from the Moon. This does not result in complete darkness, as the Moon is still partially lit by reflected Earthlight, but it does turn a deep, dark red colour.

Phases of the Lunar Eclipse that will be seen on 28 September 2015. The times are given in GMT, to the nearest 10th of a minute, thus 03.23.5 represents 30 seconds after 3.23 am GMT. HM Nautical Almanac Office.

This lunar eclipse promises to be particularly spectacular, as it occurs on the night of the lunar perigee, i.e. the night when the Moon is closest to the Earth in this lunar month making it appear larger in the sky, with the center of the Moon only 358 876 km from the center of the Earth. The Moon completes one orbit about the Earth every 27.5 days, and like most orbiting bodies, its orbit is not completely circular, but slightly elliptical, so that the distance between the two bodies varies by about 3% over the course of a month. This elliptical orbit is also not completely regular, it periodically elongates then returns to normal, making some perigees closer than others. This September's perigee will be the closest of the year, and the closest since 8 September 2015, when the center of the Moon was only 358 387 km from the Center of the Earth.

Simplified diagram of the Moon's orbit. NASA.

See also...

A partial Solar Eclipse will occur on Sunday 13 September 2015, visible from all of Namibia, Botswana, South Africa, Lesotho, Swaziland, Zimbabwe and Reunion Island and parts of Angola, Zambia, Mozambique, Madagascar and Antarctica. The eclipse will occur between 4.41 am and 9.06 am GMT.

A total Lunar Eclipse will occur on a April 2015, starting at about 9.00 am GMT. It will be visible across much of the Pacific, as well as most of Alaska, the Russian...

A total eclipse of the Sun will be visible from the Faroe Islands and Svalbard on Friday 20 March 2015, with a partial eclipse visible from the rest of Europe, West Asia, northern Arabia, North and West Africa, Iceland, Greenland and (briefly) Nova Scotia, Newfoundland and Labrador and parts of eastern Quebec. 

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