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Monday, 20 December 2010


I'll have to set the alarm for half 4 to 5 this morning:
BAA electronic bulletin
BAA e-bulletin, 2010 Dec. 19


Early this Tuesday morning, on 21 December, the day of the winter solstice,
there will be a total eclipse of the Moon. The Moon first enters the outer,
penumbral part of the Earth's shadow at 05:29 UT, and the partial eclipse
begins at 06:32 UT.  The eclipse first becomes total at 07:40 UT, reaches
maximum at 08:17 UT, and ends at 08:53 UT.

The entire eclipse will be visible after local midnight from Canada, the
USA, central America and the north-western tip of South America. The eclipse
occurs at the Moon's descending node in eastern Taurus, four days before
perigee.  The Moon will be full at 08:13 UT.  Further information on this
eclipse may be found at:

>From southern parts of the British Isles, the initial umbral phases will be
visible, but the Moon will be dropping down into the western sky as dawn
approaches.  From such locations, when totality begins at 07:40 UT, the Moon
will be very low in the west-north-western sky, close to the horizon and in
a rapidly brightening sky.  From locations in Scotland and Northern Ireland,
totality will be visible in its entirety, but the Moon will be low down
after the time of greatest eclipse (08:17 UT).

>From London, sunrise is at 08:04 UT with moonset just seven minutes later.
The table below lists the times of moonset for various locations in the
British Isles:

Location                  Moonset (UT)

Brighton                        08:08
London                         08:11
Bristol                           08:21
Birmingham                   08:25
Swansea                       08:28
York                             08:30
Liverpool                      08:35
Newcastle-upon-Tyne   08:39
Dublin                           08:48
Belfast                           08:55
Glasgow                        08:57
Aberdeen                      08:58

The umbral phase lasts from 06:32 UT until 10:01 UT.  During totality, the
Moon tracks through the northern part of the Earth's umbral shadow, so for
those observers watching it high up in a clear sky, the southern half of the
totally eclipsed Moon will most likely appear considerably darker than the
northern part.

One never quite knows how dark or how bright a lunar eclipse will be.
Everything depends on the conditions in the Earth's upper atmosphere through
which all light falling onto the shadowed Moon has to pass. There have been
eclipses when the Moon has been difficult to find even with a telescope,
while at other eclipses it has remained bright red or vividly coloured.

For observers in the British Isles, the very low elevation of the Moon
during the total phase means that it is not possible to predict the exact
brightness distribution in the umbra, so observers are encouraged to
estimate the brightness using the Danjon scale at different times during
totality. Note that it may also be necessary to assign different Danjon
values to different portions of the Moon (i.e., north vs. south).

For an explanation of the Danjon scale of lunar eclipse brightness visit:

The 2010 December 21 total lunar eclipse belongs to Saros 125, a series of
72 eclipses in the following sequence: 17 penumbral, 13 partial, 26 total, 9
partial, and 7 penumbral lunar eclipses.

There will be two total lunar eclipses in 2011, on 15 June and 10 December,
but neither will be visible in its entirety from the British Isles.

The BAA Lunar Section will be pleased to receive observations of the lunar
eclipse.  See the Section's webpage at
for more details.

John Mason
BAA Press and Publicity Officer

51 Orchard Way, Barnham, West Sussex PO22 0HX
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(c) 2010 British Astronomical Association
Good Clear Skies
Colin James Watling
Real Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork)

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