[BAA-ebulletin 00875] TOTAL ECLIPSE OF THE HARVEST MOON TONIGHT

[Rick]

[BAA-ebulletin 00875] TOTAL ECLIPSE OF THE HARVEST MOON TONIGHT
(c) 2015 British Astronomical Association    http://www.britastro.org/

In the early hours of tomorrow morning, 28 September, there will be a total eclipse of the Moon. Eclipses of the Moon occur when the Full Moon (in this case the Harvest Moon) passes through the cone of shadow cast by the Earth into space. Weather permitting this will be the first total lunar eclipse to be visible in its entirety from the UK and Ireland since 2008, and there won't be another until 2019.

The eclipse begins at 00:12 UT (01:12 BST) when the Moon enters the fainter outer part of the Earth's shadow known as the penumbra. The main phase of the eclipse begins at 01:07 UT (02:07 BST) when the Moon first enters the central, dark part of the Earth's shadow known as the umbra. It is at this stage that it will become very obvious that a lunar eclipse is underway. From London the Moon will be 35 degrees above the south-south-western horizon at this time.

The eclipse becomes total at 02:11 UT (03:11 BST) and lasts for a full 1 hour 12 minutes, ending at 03:23 UT (04:23 BST). Mid-eclipse is at 02:47 UT (03:47 BST). As the Moon will be passing through the more southerly part of the Earth's umbral shadow, it is probable that the Moon's southern limb will appear relatively bright during totality, fading to rather darker further north.

The partial eclipse ends at 04:27 UT (05:27 BST), when the Moon exits the umbra.  By this time the Moon will be only 13 degrees above the western horizon (from London)and dawn twilight will be breaking towards the east - with the brilliant Venus nicely on display if the sky is clear. The faint penumbral phase finally ends at 05:22 UT (06:22 BST).

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. The Moon appears a reddish hue because of Rayleigh scattering - the same effect that causes sunrises and sunsets to appear reddish - and the refraction of that light by the Earth's atmosphere into its umbral shadow.

This total lunar eclipse takes place at the Moon's descending node in Pisces, with the Moon just one hour past its closest approach to Earth in 2015 at mid-eclipse, an event that is nowadays often called a 'supermoon', although this term is not particularly well defined. The Moon's apparent diameter will be 33' 28".

Some further information on this eclipse may be found on page 14 of the 2015 BAA Handbook, and also at:

http://eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2015Sep28T.pdf

Please send any images or other observations of this event to the BAA Lunar Section.

This e-bulletin issued by:
Dr John Mason
BAA Press and Publicity Officer
2015 September 26

[Rick]

Corrections applied to paragraph beginning "The eclipse begins at ..."