Stargazers across the Earth are in for a huge treat at the end of July, the longest lunar eclipse – or Blood Moon – in roughly a century is about to happen.
Starting the evening of July 27 and going into the early morning of July 28, the Earth will pass between the Sun and the Moon, casting a huge red shadow on the lunar surface.
The shadow’s red because, while the Earth blocks the light of the Sun from reaching the moon, the only light being reflected by the lunar surface has been refracted by the Earth’s nitrogen-rich atmosphere.
Due to a scientific phenomenon known as Rayleigh scattering – the same mechanism which makes the sky blue and sunsets red – the light refracted by the Earth looks red.
David Diner, a planetary scientist at NASA’s Jet Propulsion Laboratory, wrote on his blog:
If you were standing on the moon’s surface during a lunar eclipse, you would see the sun setting and rising behind the Earth.
You’d observe the refracted and scattered solar rays as they pass through the atmosphere surrounding our planet.
The effect is further exacerbated by the glass-like rock dust covering the Moon’s surface, which has a special property called ‘backscatter’, which allows it to reflect light back to where it came from.
So, during a total lunar eclipse, what we’re seeing is the Earth’s refracted sunset-sunrise light being bounced right back at us.
Depending on the position of the Moon in relation to the Earth, the shadow can take on a variety of colours from a deep copper-ish red, to a vibrant orange.
It’s not only the moon’s position that can change the colour of the light, David Diner says human activity can also play a part.
Pollution and dust in the lower atmosphere tends to subdue the color of the rising or setting sun, whereas fine smoke particles or tiny aerosols lofted to high altitudes during a major volcanic eruption can deepen the color to an intense shade of red.
Whether you can see the lunar eclipse is going to depend on where you are in the world.
If you’re in North America then apologies, but unless you’re watching it on TV, you’re not going to see it.
Those living in, eastern Asia, Europe and Australia will get a partial lunar eclipse, where the moon only passes partly through Earth’s shadow.
But if you call the Middle East, central Asia, Antarctica or eastern Africa home, then you should be able to see the full lunar eclipse.
According to NASA, the whole thing will begin at 17:14 Universal Time on July 27, when the moon first touches the penumbra – or outer shadow – of Earth.
The moon will be completely inside the shadow of the Earth by 19:30 UT and will remain there for a full 1 hour 43 minutes before it starts to pass.
The whole event will be over by 23:28 UT, early on July 28, depending on where you live in the world.
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