Question
Sirius seemed to be blinking a lot in late September. I also think it blinked from green to red and white. Is this some new phase Sirius is in?
Answer
Nothing has changed with Sirius. You just observed an unusual amount of twinkling. Earth’s atmosphere is not uniform, but instead has cells of different densities and temperatures. As starlight passes through the atmosphere, the light beam is constantly redirected by refraction, and since the cells are in motion, the path of light is changing all the time. The jumping around is one aspect of twinkling, called “seeing.” The other aspect, called “scintillation,” is changes in brightness and color.
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