Total eclipse of the Moon to be seen from South Devon

By David Love, on Tuesday, May 31, 2011

Lunar eclipse: a total eclipse of the Moon is coming to South Devon

The people of South Devon will be able to view a total eclipse of the Moon on the evening of Wednesday, June 15. Total eclipses of the Moon are not nearly as spectacular as total eclipses of the Sun, but they are still worth watching.

They occur whenever the Earth is positioned directly between the Sun and the Moon, and the Earth’s shadow falls on to the surface of the Moon.

If the Earth had no atmosphere, then the Moon would seem to disappear completely when in the Earth’s shadow. It doesn’t disappear, because some light from the Sun is refracted (bent) through the Earth’s atmosphere, and on to the Moon’s surface.

Depending on atmospheric conditions, this will often give the Moon a reddish tinge (because red light is refracted more than other visible wavelengths). This is an effect that was first explained by the 17th century German astronomer Johannes Kepler. The photo of a recent lunar eclipse (from the Torbay Astronomical Society website) shows this reddish effect.

The total eclipse will already be in progress when the Moon rises in the east over Devon at about 9.23pm. Totality will come to an end at about 10.02pm, and the Earth’s shadow will then slowly start moving off the Moon’s surface. Watch out for the edge of the shadow.

You should be able to detect that the edge of the shadow forms part of a circle. The only shape that will always cast a circular shadow, no matter from what angle, is a sphere. This was one of the observations that persuaded Pythagoras, an ancient Greek who lived in the 6th century BC, that the Earth is spherical, not flat – something that has been accepted by educated people throughout Europe ever since.

So if you ever harboured any suspicions that the Earth is flat – this is an opportunity to dispel them.

(image of a lunar eclipse courtesy of the Torbay Astronomical Society)