In a partial lunar eclipse, the Earth, Sun and Moon are almost exactly in line and the Moon is on the opposite side of the Earth from the Sun. The Moon is full but moves partly into the shadow of the Earth and dims dramatically with the shadowed portion of the lunar surface lit by sunlight that passes through the Earth’s atmosphere.
Stronger atmospheric scattering of blue light means that the light that reaches the lunar surface has a reddish hue, so observers on Earth will see a Moon that is partly light and partly dark, with hints of colour that depend on terrestrial conditions.
The Moon travels to a similar position every month, but the tilt of the lunar orbit means that it normally passes above or below the terrestrial shadow. A Full Moon is seen but no eclipse takes place.
Lunar eclipses are visible wherever the Moon is above the horizon. This eclipse will be best seen from most of Africa, Eastern Europe, central Asia, India and the Middle East. From Western Europe and the United Kingdom, the Moon will rise during the eclipse.
It begins at 1923 BST when the Moon enters the lightest part of the Earth’s shadow, the penumbra. Soon after the Moon will have a slight yellowish hue. From London the eclipsed Moon will be visible after it rises at 2011 BST while observers in Glasgow will see it from 2040 BST. The Moon enters the darker part of the terrestrial shadow, the umbra, at 2036 BST. Greatest eclipse is at 2210 BST, when more than 80% of the visible side of the Moon will be within the umbra and the remainder within the penumbra. The Moon leaves the umbra at 2344 BST and finally the eclipse finishes when it exits the penumbra at 0057 BST (on 17th August).
During the eclipse the Moon lies in front of the stars of the constellation of Capricornus and to its right will be the planet Jupiter. From the UK, the Moon will be fairly low in the sky throughout the event, so the eclipse promises to be a beautiful sight presenting good opportunities for photographers. And unlike an eclipse of the Sun, the whole event is quite safe to watch and needs no special equipment.
Robert Massey | alfa
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