Why is the sky blue?

Space is fascinating, isn’t it? At night when you gaze up you can spot planets, glowing stars, and galaxies all against a vast black backdrop. This is doable even without a telescope.  However, when the sun rises, this scenic view of space begins to fade and it makes way for the blue sky of day.  But what gives?!  You know that space hasn’t disappeared. You know it is still there, waiting for you to get past number 3,987 in your star count. Sure, the much brighter sun makes it harder to count the other stars during the day, but why did the sky choose that color? Isn’t sky blue old fashioned, it is so last eon, according to universal fashion standards.  So, why is the sky blue?

The sky is blue because of the combination of Earth’s atmosphere and sunlight. The majority of Earth’s atmosphere is composed of two gasses, oxygen (of course, we need it to breathe) and nitrogen. The two gasses are really small. Sunlight is made of all the other possible colors of light such as red, orange, purple, and blue. Because light travels in waves, every color of light has a different wavelength . Red, on one end of the color spectrum, has a long wavelength, while violet, on the other end, has a short wavelength. When direct sunlight hits the small particles of oxygen and nitrogen, part of that light is scattered. In the scattered light, the shorter wavelengths are diffused more so than the longer wavelengths. This results in more blue light reaching the surface of Earth and our eyes. We don’t see a lot of purple because oxygen absorbs colors with even shorter wavelengths, like violet.

So, it seems that we shouldn’t judge the sky’s style too harshly. Its true colors are determined by what is on the inside …of its atmosphere.  If the atmosphere was composed of different gasses or particles, it would have different colors.  For example, Mars has a much thinner atmosphere than Earth’s and almost all of it is composed of Carbon Dioxide and dust. This combination gives Mars an other-worldly orange and red color.  Spooky!  I don’t know about you, but I think sky blue is more chic than orangish-red. 

By Mark Smith