"Every night before bedtime, I take my dogs outside to do their doggy business, letting them run around in the yard on the eastern side of my house. I live under very dark skies in rural Virginia, and even though I'm a card-carrying astronomer, it's always a shock to look up and see so many stars. In the winter my eyes are usually drawn to the brightest stars such as Betelgeuse and Rigel in Orion and Aldebaran in nearby Taurus."
"They aren't just bright; they're also colorful, standing out against the standard white appearance of most other stars in the sky. Betelgeuse is red-orange, Aldebaran is orange, and Rigel is sapphire blue. As I wrote in a previous The Universe column, The Colors of Stars, Explained, only the brightest stars give off enough light to activate our eyes' cones, the color-sensitive cells in the retinas."
"On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. What you won't see, though, are green ones. The reason for this is both a fault in the stars and in ourselves: we don't see them as green because of the way stars emit light and the way our eyes see colors."
Bright stars can show distinct colors—red-orange Betelgeuse, orange Aldebaran, and blue Rigel—because stellar temperature shapes emitted light. Stars radiate broadly as blackbodies, with cooler stars peaking at red wavelengths and hotter stars peaking at blue. Only the brightest stars stimulate cone cells in human retinas, allowing perceived color; fainter stars appear white. Photographic images reveal stellar colors for many stars. Human eyes rarely perceive stars as green because blackbody spectra that peak in green still emit enough red and blue to produce a white or non-green appearance when combined with cone responses.
Read at www.scientificamerican.com
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