Sunset

by Marc Cornwall (photos by Errol Rickmann)

Sunsets. They are an amazing sight. The sunset sky's fine blend of violet through pink pastels and striking oranges eclipse the canvases of Earth's greatest artists - present, past, and probably future. The Sun itself transforms from a searing yellow white hot source of light and heat into a large elliptical cauldron of orange boiling lava, massaging you senses with a gentle heat. Almost like it undergoes billions of years of its evolution from a G class star into a an M class red giant in the space of a few hours!

Sunset in Kingston, Jamaica. Credit: Errol Rickmann

What is going on here?

The Sunset's divine tapestry is caused by the interaction of sunlight with Earth's atmosphere and... by us! Yes, you and I.

First, let's discuss the colours. As the sun travels across the sky from close to the zenith to the horizon, sunlight increasingly encounters more atmosphere. The particles in the atmosphere scatter the shorter wavelengths of sunlight, leaving only the red wavelengths to end up in our eyes. (Ever seen a rainbow? The violet to green light is is shorter wavelength, the yellow to red light is longer wavelength.) The scattering is called Rayleigh scattering. If you're feeling brave you can read bout it and more here. Notice in the picture below how the "sunset line of sight" travels a longer distance than the "midday line of sight" through the (blue) atmosphere. The Earth rotates anticlockwise from "you at midday" to "you at sunset."

The "sunset line of sight" travels a longer distance than the "midday line of sight" through the (blue) atmosphere. The Earth rotates anticlockwise from "you at midday" to "you at sunset."

Now let's discuss how you and I affect the sunset. To be more precise we're going to discuss how the way we see the world makes us see the Sun bigger on the horizon, than when it's high in the sky. (The same thing happens with the Moon by the way.) This known usually as the Moon Illusion. See nice descriptions of it here and here but if you prefer pictures, which are worth 1000 words, then just take a look at the pictures below, and then say "wow!"

Which of these spheres is the bigger sphere? Chosen your answer? See answer below.

None of these spheres are bigger. Check for yourself. Use something to measure. This is the essence of our perceiving the Sun as bigger on the horizon.

So next time you see a sunset, like the ones pictured here, remember how they come about and say "wow."

Sunset in Kingston, Jamaica. Credit: Errol Rickmann