Asked by AlexChemistry ⚛️

Why is the sky blue?

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Rima Ranu

4 years experience working in primary schools and SATS tutoring.

The sun emits light and this travels to our earth in a straight line. The light contains the entire spectrum of colours and each colour has a wavelength. When the light reaches earth, the shortest wavelength blue gets reflected off of gas molecules like oxygen in our sky. We see this blue when the blue light that the molecules reflected get scattered in different directions. The longer wavelengths like red and orange pass through and don’t bounce off any molecules so we don’t see the colour in the sky. This is called Rayleigh scattering after the physicist who came up with this idea.

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Rima Ranu

4 years experience working in primary schools and SATS tutoring.

The sun emits light and this travels to our earth in a straight line. The light contains the entire spectrum of colours and each colour has a wavelength. When the light reaches earth, the shortest wavelength blue gets reflected off of gas molecules like oxygen in our sky. We see this blue when the blue light that the molecules reflected get scattered in different directions. The longer wavelengths like red and orange pass through and don’t bounce off any molecules so we don’t see the colour in the sky. This is called Rayleigh scattering after the physicist who came up with this idea.

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Joseph John Fernandez

I love maths and physics, but I love helping people understand them even more!

Due to Rayleigh scattering. When sunlight enters the atmosphere it encounters small air molecules. In summary, when light encounters the particles it changes the direction of the beam. The effect depends on 1/wavelength ^4, a strong inverse dependence. Blue light has the smallest visible wavelength, hence its photons are scattered the most. Therefore, it seems like blue light comes from all over the atmosphere!

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Mike Jones

PhD at University of Oxford in Theoretical Physics

Light from the Sun appears white but it actually consists of many different colours. We can see these different colours of light in a rainbow or when white light passes through prism. As the white light from the Sun travels through the Earth’s atmosphere, it collides with particles of air.  The different colours, or wavelengths, of light are scattered by these collisions by different amounts.  Blue light (shorter wavelengh) is scattered more than red light (longer wavelength). So, when the Sun is high in the sky, blue light is scattered in all directions as sunlight passes through the atmosphere and we see the sky as blue

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