Eclipse 2018: How the Blood Moon changes to red colour in lunar eclipse | Science | News


The will light up the night skies above Earth in the late hours of Friday, July 27.

During the eclipse, the moon will cross paths with the centre of Earth darkest shadow, its umbra, and briefly vanish from sight.

But rather than completely vanish from the skies for a period of time, the full moon will take on a deep red to orange colour.

The bizarre Blood Moon spectacle will be visible throughout the entirety of the greatest eclipse which will last about one hour and 43 minutes.

But why does the moon change colour during a total lunar ?

A lunar eclipse occurs whenever the moon and the sun perfectly align on the stellar planes with the earth right in the middle of the two.

In this position, the Earth obscures all sunlight falling on the moon, producing a cone of dark shadow extending into space.

It would make sense to assume the moon will stay shrouded in the shadow but a trick of light, known as Rayleigh Scattering, illuminates the moon red.

Throughout the eclipse rays of sunlight cast by the sun are bent and scattered around the Earth’s atmosphere.

The scattering light filters out certain bands of colour on the visible spectrum, such as blue, leaving the least affected colours like red and orange to fall on the moon.

According to NASA’s Goddard Space Flight Centre, if you were to look at the Earth from the surface of the moon, the Earth would be circled by a bright corona of orange light – every single sunrise and sunset on the dayside of the planet.

The US space agency said: “As the moon passes into the central part of the shadow, called the umbra, it darkens dramatically.

“Once it’s entirely within the umbra, the moon appears a dim red due to sunlight scattered through the Earth’s atmosphere.

“In fact, if you watch the eclipse from the surface of the moon, you’d see the sun set behind the entire Earth, bathing you in a warm red glow.”

The same scattering of light is responsible for the blue colour of the sky, the colour of blue eyes and orange sunsets.

Rayeigh Scattering is named after 19th Century British scientist Lord Rayleigh.

Richard Fitzpatrick, professor of physics at the University of Texas in Austin, explained: “When the sun is low in the sky, it appears less bright, due to atmospheric scattering.

“However, it also appears redder than normal, because more blue light than red light is scattered out of the solar light-rays, leaving an excess of red light.

“Likewise, when we look up at the sky, it does not appear black because of light from solar radiation which grazes the atmosphere being scattered downward towards the surface of the Earth.

“Again, since blue light is scattered more effectively than red light, there is an excess of blue light scattered downward, and so the sky appears blue.”

The intensity of the Blood Moon is also affected by other factors such as atmospheric conditions and the amount of dust in the air.



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