One of the pleasures of stargazing is noticing and enjoying the multitude of stars in the dark skies. You may notice that while most stars, especially the fainter ones, appear white, many stars display different colors. Why is this?
Why Do Some Stars Have Colors?
The different hues offer direct visual evidence of how stellar temperatures vary. A good many of the winter luminaries —such as most of the bright ones in Orion—are blue, but we can easily find other contrasting colors there as well.
Look at reddish Betelgeuse, orangish Aldebaran, and yellowish Pollux. And considerably removed from this winter grouping is the brilliant topaz Arcturus holding forth in solitary splendor in the east. Even as you observe these stellar colors, do you notice that they’re recognizable only for the brightest stars? This is due to the physiology of the eye, more specifically, the fact that the color sensors on the retina – the cones – are insensitive to faint light.
Under dim illumination, the retinal rods take over. But their greater light sensitivity is offset by their color blindness. This is why we see all faint stars as white. However, if we look at them through binoculars or a telescope, their amplified brightness stimulates the cones, which detect their color.