Blood Moon Rising
September starts off in style for stargazers with an eclipse of the Moon.
At full eclipse, the Moon may turn red, a ‘Blood Moon’.
When we see the eclipse in the UK, the Moon will be rising in the east.
There will be a Blood Moon rising!
What causes an eclipse of the Moon?
An eclipse of the Moon – a lunar eclipse – happens when the Moon passes through the shadow of the Earth.
It always happens at Full Moon, the phase when the Moon is fully illuminated by the Sun.
This happens when the Moon is on the opposite side of Earth to the Sun.
Also lit by the Sun, our Earth casts a dark shadow into space.
When the Moon passes through the shadow, the umbra, we see an eclipse.
As it moves into the shadow and out again, we see a partial eclipse.
Over a couple of hours on September 7th, we’ll see totality become partial.
How frequent are lunar eclipses?
A lunar eclipse happens at Full Moon.
There’s a full Moon every month so it looks as though there should be an eclipse every 28 days.
That’s clearly not the case. Lunar eclipses are much less common.
The reason is that the Moon’s orbit is tilted slightly to Earth’s orbit round the Sun.
The tilt is small, about 5 degrees.
It’s only when the Moon happens to cross Earth’s orbit at full Moon that we see an eclipse.
As a result, eclipses only happen about twice a year.
The last one happened on March 14th this year.
Time and Place
The Moon will already be in total eclipse when it rises on September 7th.
In the UK, that’s around 7.40pm.
Totality will end at about 7.50pm so there’s a only short window of totality for us.
After that we’ll see the Earth’s shadow slowly move across the Moon.
That shadow will be gone at around 9.55pm.
The eclipse is then over, leaving a bright Full Moon.
The Moon rises in total eclipse.
So you will need a clear horizon to the east to see the full Blood Moon.
Why does the Moon turn red?
You would expect that when the Moon is in Earth’s shadow, it would be dark.
With no sunlight illuminating the surface, it should be black.
At totality, the Moon should simply disappear.
But it turns red.
The Moon turns red because some sunlight is bent by the Earth’s atmosphere.
Red wavelengths in the Sun’s light are refracted most.
That red light gives a crimson illumination to the Moon.
The hue can vary but at its most intense, we get a splendid ‘Blood Moon’.
Good Luck!
I hope that your sky is clear on September 7th.
The lunar eclipse is certainly worth seeing.
It’s quite a wait until the next one.
The next total eclipse of the Moon will be on 31st December, 2028.
A Personal Note
In June this year I became an MBE, a Member of the Order of the British Empire.
The award was for over 50 years service to Astronomy Education.
I feel very honoured and look forward to my investiture later this year.
Maybe I’ll write a blog about it!
The author: Dennis Ashton, MBE, is a Fellow of the Royal Astronomical Society and a Wonderdome presenter.
In 2024, Dennis received the Special Contribution award from the British Association of Planetaria.
Wonderdome now has 15 presenters, making us the largest – and best – mobile planetarium organisation in the UK.
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