It's important to note that twilight refers to the whole time period between sunset and darkness, not just the early part. You can keep playing baseball, tennis, cricket, etc outside in the early twilight, but by dusk it would be really hard to see the ball without artificial lights. It refers to this entire time period, while dusk specifically and only refers to the last part of this time period, eg when it is starting to get really dark. So twilight is after the sun sets and before it gets dark. The period of the evening when twilight is visible, between daylight and darkness. These effects are a cause of Rayleigh Scattering.The soft glowing light from the sky when the sun is below the horizon, caused by the reflection of the sun’s rays from the atmosphere. The shorter wavelength blue light is scattered further, as the sunlight passes over a greater distance, and we see the longer wavelength yellow and red light.
However, at sunset, light has further to travel through the atmosphere. Reaching Earth's atmosphere, it is scattered in all directions, therefore we see blue sunlight. Blue is scattered more than other colours because it travels as shorter, smaller waves. The diagram below shows that at midday, light has less atmosphere to travel through.
This means that there is relatively more yellow and red light left for us to see. Because blue light is scattered more strongly by the atmosphere, it tends to be scattered several times and deflected away in other directions before it gets to us. Why is the sunset red or orange?Īt sunrise and sunset, the Sun is very low in the sky, which means that the sunlight we see has travelled through a much thicker amount of atmosphere. For example, blue has a short wavelength, while red is created by longer wavelengths. Light that looks white to us, is actually made up of many different colours of differing wavelengths. Light travels from the Sun and through the atmosphere in invisible waves.
To begin, we need to understand how we see colour.
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