Why is the sky blue? Light and other electromagnetic waves can interact with particles smaller than the wave itself creating a phenomenon called Rayleigh scattering. Light waves travelling from the sun to the earth interact with particles in the atmosphere to create diffuse sky radiation giving the sky its blue color and the sun a yellow hue. Nearby, only 100 light years away, the exoplanet GJ 3470b shows blue skies, signs of Rayleigh scattering. Astronomers know that GJ 3470b is a transiting in front of a nearby star, enough to change the amount of light we receive from that star. After taking a spectrum of the wavelengths created by the light traveling through the atmosphere of this planet researchers were able to determine what the atmosphere looked like in terms of color and opacity. From this they were able to determine that the atmosphere surrounding the planet was a blue color. This is significant for a couple main reasons, one being that this planet is the smallest exoplanet for which a blue, complete atmosphere is found, about 4 times the size of Earth. This is exciting because there is now reason to believe there is a hydrogen rich atmosphere. 
More information can be found at phys.org | dailymail.co.uk
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