Keep an eye out for the Moon passing into Earth’s umbral shadow after 02:07 BST. Image credit: Pete Lawrence
In a total lunar eclipse, the Earth, Sun and Moon line up, with Earth in the middle.
The full Moon moves into Earth’s shadow and dims, but remains visible as a result of the sunlight passing through the Earth’s atmosphere.
This results in a Moon that can appear red in colour, or sometimes dark grey depending on conditions.
This year’s lunar eclipse will be a three-fold event.
It will be a perigee-syzygy Moon, meaning it is a full Moon occurring at the closest point in the lunar orbit to Earth.
It is also the largest full Moon of the year, with an apparent diameter of nearly 33.5 arc minutes, and is the closest full Moon to the northern hemisphere’s autumn equinox, making it the 2015 Harvest Moon.
Lunar totality typically takes over an hour to complete, making it a much slower affair than a solar eclipse.
In fact, totality for the event on the morning of 28 September should take a total of three hours and 20 minutes to fully play out.
It’s even longer if you take into account the weak penumbral phase of the eclipse, which is when the Moon passes through the lighter outer part of Earth’s shadow.
However, this phase is barely noticeable to the naked eye and is best captured with a camera.
Taking this phase into account, the eclipse will last around five hours and 10 minutes.
The penumbral phase starts at 01:12 BST (00:12 UT) when the Moon will be about due south and 37º up as seen from the centre of the UK.
First umbral contact will occur an hour later at 02:07 BST (01:07 UT).
In the run-up to this stage, the western part of the Moon’s disc will begin to appear darker than usual.
This is because the edge of the umbra (the inner section of total darkness) is blurred rather than sharp, creating a fuzzy shaded edge as the eclipse begins to take shape.
The umbral shadow will then begin to cross the lunar disc between 02:07 to 03:11 BST (01:07 to 02:11 UT), at which time totality will be reached.
The Moon will pass through the southern portion of the umbral shadow during the eclipse, so the southern limb will appear lighter than the northern one.
At greatest eclipse, the northern limb will almost mark the centre of the umbral shadow.
Greatest eclipse occurs at 03:47 BST (02:47 UT) when the Moon is in the southwest, 27º up.
Totality will end at 04:23 BST (03:23 UT) when the Moon reaches the southeast edge of the umbral shadow.
The second partial phase begins and lasts until 05:27 BST (04:27 UT), when the Moon finally leaves the umbral shadow.
At this stage, the Moon’s altitude will be 15º and dawn will have begun.
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