Sky Colors for Exo-Earths

February 03, 2009


Photographer: Ivan Gonçalves
Summary Author: Ivan Gonçalves

This photo montage shows the color of the sky for an exo-earth (earth-like planet orbiting another star) depending on the type of spectrum of its host star - given that the planetary atmosphere is identical to ours. The spectrum of the star is likened to that of a black body, and sky color is calculated by taking into account Rayleigh scattering. Computations are valid for the human eye. The apparent diameter of the host star is calculated according to its actual diameter (function of mass and temperature) and by considering the planet's orbit within the habitable zone of the star.

It can be seen that the sky is blue for a star with temperature above 3,300 K; the sky is white near this temperature (as would be the case for star GL 581, where "super-earths" were recently discovered); the sky is yellow, orange and red for temperatures below 3,300K. The photograph of the landscape is taken near the birthplace of Leonardo da Vinci, between the Tuscan cities of Pistoia and Empoli in north central Italy.