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

[BAA electronic bulletins service]

TOTAL ECLIPSE OF THE HARVEST MOON TONIGHT

 

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 Moon'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 Moon'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