Total Lunar Eclipse

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This Friday (the 27th of July) the Moon will rise into view in the south east around 9.30pm with an unusual red colour. This is due to a rare phenomena known as total lunar eclipse – when the Earth sits directly between the Moon and the Sun.

But why doesn’t the Moon darken if its light supply is cut off by the Earth, and why will it turn a red colour?

The best way to think about this is to imagine yourself standing on the surface of the Moon as the Earth slowly passes in front of the Sun.

As the disc of the Earth begins to occult the Sun it will start to darken until finally the whole of the Earth sits in front of the Sun. But as this takes place something amazing happens. The Earth’s atmosphere refracts the sunlight into an intense circle of vibrant sunset. It’s this ring of fire around the Earth that illuminates the Moon during totality, giving it an eerie red colour.

This far north between 9.30pm and 10.30pm it’ll still be pretty bright outside but the colour change should still be obvious to see. As the evening progresses the eclipse will become partial and will be almost over by midnight.

Totality for this lunar eclipse will be 103 minutes making it the longest in this century. As my animation below shows we won’t be able to witness the start of this eclipse, only its middle and end.

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Times:

Peak Eclipse 9.21pm
Moonrise (at 57 deg north) 9.35pm
Total eclipse ends 10.13pm
Partial eclipse ends 11.19pm
Eclipse ends 12.28am

Clear skies and happy Moon watching!

 

Super Blue Blood Moon

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So what’s a ‘Super Blue Blood Moon’?

It’s a combination of three lunar phenomena. A blue moon is when two full moons fall in the same calendar month, which isn’t very often (roughly once every 3 years) hence the expression ‘once in a blue moon’. The ‘super’ is because the full moon is occurring at a close approach to earth (formally within 10% of orbital perigee). Finally the blood part indicates there’s also a lunar eclipse, although we won’t witness it from Highland skies.

One of the amazing things when witnessing a lunar eclipse is the blood red colour the moon takes as sunlight refracts around earth’s atmosphere.  This is really an extreme form of earth shine, when we can see the shadowed areas of the moon due to sunlight reflected from earth.  I always like to imagine what a lunar eclipse would look like from the surface of the moon.  As the earth completely obscured the sun you would see a brilliant ring of red light radiating around the black disc of the earth.  The lunar landscape around you would be bathed in an eerie red light.

The blue moon phenomena is interesting when you consider we now use a solar calendar.  Around 40BC Julius Caesar severed the old link with the moon, so that months (or ‘moon-ths’)  no longer coincided with the phases of the moon.