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A lunar eclipse at sunrise

Last Updated on Thursday, 24 November 2011 15:01
Published on Sunday, 19 December 2010 18:04

People in the UK will have the chance to see a total eclipse of the Moon at sunrise on the morning of 21 December, the date of the winter solstice. Unusually, for British observers this eclipse includes a brief period when both the Sun and eclipsed Moon are above the horizon and precisely opposite each other in the sky.

 

lunareclipse_20010109_ndj
An image of the lunar eclipse of 9 January 2001. Credit: Nick James
In a total 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 into the shadow of the Earth and dims dramatically with the shadowed 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 tends to have a reddish hue, so observers on Earth will see a Moon that is much darker than usual, 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 time the entire eclipse will be visible from the whole of North America, the eastern Pacific and the northwest of South America. From western Europe, including the UK and Ireland, the Moon will set during the eclipse as the Sun rises.

It begins at 0528 GMT (all times that follow are GMT) when the Moon enters the lightest part of the Earth’s shadow, the penumbra. Soon after the Moon should have a slight yellowish hue. The Moon enters the darker part of the terrestrial shadow, the umbra, at 0632.

The total phase (totality) begins when it is completely immersed in the umbra at 0740. From London, the Moon will then only be 3 degrees above the northwestern horizon, so observers will need a good unobstructed view to see it. In the northwest of the UK, the prospects are better. In Glasgow at the same time, the Moon will be 7.5 degrees high and in Stornoway in the Western Isles the Moon will be about 10 degrees above the horizon.
 
By this time the sky will be brightening as sunrise draws near, which in London happens at 0804, in Glasgow at 0846 and in Stornoway at 0912. In the three locations, the Moon sets at 0812, 0857 and 0925 respectively. Totality ends at 0854, meaning that Londoners will miss the later part of totality, Glaswegians will potentially just about see the whole total phase and residents of the Western Isles could enjoy an even better view.

In the later phases of the eclipse not visible from the UK, the Moon leaves the umbra at 1002 and the eclipse finishes when it exits the penumbra at 1106.

During the eclipse the Moon lies in front of the stars of the constellation of Taurus, although these will be increasingly hard to see in the twilight sky and will be invisible after sunrise. However, the low altitude of the Moon offers some photogenic opportunities for photographers to image the Earth’s natural satellite in eclipse next to more familiar terrestrial landmarks. And unlike an eclipse of the Sun, the whole event is quite safe to watch and needs no special equipment.

FURTHER INFORMATION

HM Nautical Almanac Office eclipse website: http://www.eclipse.org.uk
HM Nautical Almanac Office websurf calculator (includes sunrise and sunset times, lunar phases and positions of planets): http://websurf.hmnao.com/

CONTACTS

Dr Robert Massey
Royal Astronomical Society (based in London)
Tel: +44 (0)20 7734 3307 x 214
Mob: +44 (0)794 124 8035
Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

Steve Owens
Freelance Astronomer (based in Glasgow)
Mob: +44 (0)7879 058 120
Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

NOTES FOR EDITORS

The Royal Astronomical Society (RAS, www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3500 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.