CATCHING SOME RAYS: Crepuscular rays in the evening over Warwick.
CATCHING SOME RAYS: Crepuscular rays in the evening over Warwick. Terry West

Don’t you love a little ray of sunshine?

WHO loves sunsets and the rays protruding from the point of the sun at sunrise and sunset? Did you know these rays have a name? They are called crepuscular rays.

They stream through gaps in the clouds and other atmospheric conditions and appear to us as rays of sunlight separated by darker regions.

Dust in the atmosphere, water vapour in the form of clouds and aerosols in the atmosphere are just a few of the reasons we see them. They also appear to radiate from one point in the sky where the sun is but this, in fact is not true.

These rays are almost parallel as they stream across the sky.

This is due to a perspective effect. Imagine you are standing on a railway track and you look down the track into the distance.

The two rails appear to converge on the horizon and this is the same effect that we see with crepuscular rays. the name crepuscular comes from the Latin word, "crepusculum" meaning twilight and the hours between dawn and dusk are known as The Crepuscular Hours.

As the rays are most frequently seen at these times, the name crepuscular has been given to these rays. On occasion they can be seen during the day if it is cloudy and the cloud has gaps.

On rare occasions these rays can be seen on the horizon opposite the sun. These are known as anti-crepuscular rays and are not easy to spot.

They appear to converge at the anti-solar point, on the horizon but in reality, they are almost parallel.

Sunrise and sunset crepuscular rays almost always appear red or yellow because at that time the light is travelling through the thickest part of the atmosphere compared to midday.

Dust, water vapour and other objects in the atmosphere scatter the short wavelength light while allowing the longer wavelengths, red and yellow, through.

This is known as rayleigh scattering. It describes the elastic scattering of light by particles much smaller than the wavelength of the light.



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