Total Lunar Eclipse September 2015

28 September 2015

Lunar eclipses can only happen at Full Moon since this is when Sun, Earth and Moon are perfectly lined up (termed syzygy).

Earth casts a penumbral shadow (where from the Moon the Earth is only partially occulting the Sun’s disk) and an umbral shadow (where the Sun is completely hidden as seen from the Moon).

The penumbral shadow dims the Moon only slightly and is difficult to detect. The darkness of the umbral shadow varies from eclipse to eclipse depending on various factors that affect how much residual light is refracted around the Earth by its atmosphere. The light that is refracted is predominantly red, which gives the totally eclipsed Moon its coppery colour.

Earth’s shadow cone at the distance of the Moon is over twice the size of the Moon (its curvature can be seen in the above images) so as the Moon moves along its orbit (moving roughly its own diameter in an hour) it passes into and out of Earth’s shadow, typically taking a few hours to do so.

In this case the umbral shadow began to eclipse the Moon around 2.15AM local time. The Moon became totally immersed in umbral shadow about an hour later, and began to emerge an hour after that.

Note that the Moon actually passes through the shadow from west to east, but due to my camera setup and its changing geometry during the eclipse, this is not depicted in the montage.

Images of the umbral phase taken from Cheshire UK.
Nikon D810A, Nikkor 80-400 plus x2 converter at 800mm zoom.