Observations

Moon to lose big bite on Saturday night – the partial lunar eclipse of 26 June 2010

The Moon during the peak of the partial lunar eclipse at 9:38 pm on 26 June 2010

The Moon during the peak of the partial lunar eclipse at 9:38 pm on 26 June 2010. The main maria or seas on the Moon are indicated. Image Nick Lomb using Stellarium software and with information from Harry Roberts’ Moon map in the 2010 Australian Sky Guide.

When is the eclipse?
There is a partial eclipse of the Moon on the evening of Saturday 26 June 2010. The eclipse is visible from anywhere in Australia and is completely safe to watch. It begins at 8:16 pm AEST and ends at 11:00 pm. At the peak of the eclipse at 9:38 pm just over half the Moon’s width will be eclipsed.

How do eclipses occur?
Eclipses of the Moon occur when the Moon moves into the shadow of the Earth. When the Moon is fully immersed in the dark part of the shadow we see a total eclipse of the Moon. At such times the eclipsed Moon usually takes on a dark reddish colour from the light bent or refracted onto the Moon by the Earth’s atmosphere. When the Moon is only partially immersed in the dark part of the shadow, like tonight, we have a partial eclipse.

How eclipses of both the Sun and Moon occur. Sketch Nick Lomb

How eclipses of both the Sun and Moon occur. Sketch Nick Lomb

An eclipse of the Moon can only happen at full Moon phase. It does not happen every month as the path the Moon takes around the Earth is tilted by about 5° to the path the Earth takes around the Sun. Hence at full Moon the Earth’s shadow usually falls below or above the Moon.

What is the history of Moon eclipses?
Eclipses of the Moon first provided proof that the Earth is a globe as the edge of the Earth’s shadow moving across the Moon is always part of a circle. This was noticed by the Greek philosopher Aristotle who lived in the fourth century before our era.

According to ancient Chinese legend an eclipse of the Moon occurs when a dragon begins eating the Moon. Hence the tradition in China during eclipses was to make as much noise as possible by banging on drums and pots to scare away the dragon. This technique has so far succeeded on each occasion.

Features on the Moon
With the unaided eye you can see dark patches on the Moon – these are the maria, Latin for seas, as they were once thought to contain water. The eclipse provides a good opportunity to identify these features as they are covered and then uncovered by the Earth’s shadow – see the annotated drawing of the Moon above drawn for the peak of the eclipse at 9:38 pm. Mare Tranquillitatis or Sea of Tranquillity was where the American astronauts Neil Armstrong and “Buzz” Aldrin landed on the Moon in July 1969.

Seeing and photographing the eclipse
It is safe and fun to do yourself and you can do so from anywhere in Australia. However, if you are lucky enough to live in Sydney you have the opportunity to do so from Sydney Observatory. The Observatory will be open for viewing of the eclipse through telescopes and there will be the opportunity to take photographs as well.

Partial eclipse of the Moon
Saturday 26 June
8pm – 11pm
A partial eclipse of the Moon, visible across the continent, takes place on the evening of Saturday 26 June. The Moon enters the Earth’s shadow at 8:16pm and leaves the shadow at 11:00pm. The evening includes telescope viewing and short talks about the Moon. Hot drinks and snacks will be available for purchase.
Cost: $15 adult, $12 conc., $10 child, $45 family.
Members: $13 adult, $10 conc., $8 child, $34 family.
To make a booking, telephone 9921 3485

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