When you buy through links on our articles, Future and its syndication partners may earn a commission.Why do stars shine different colors in the night sky?. | Credit: zhengshun tang via Getty ImagesOne of the pleasures of stargazing is noticing and enjoying the various colors that stars display in dark skies.Star colors are always interesting to observe, since they add so much to the character of the constellations. These hues offer direct visual evidence of how stellar temperatures vary. A good many of the luminaries of the summer season — such as brilliant Vega, which stands about halfway up in the east-northeast sky as darkness falls — are bluish white. Still, we can easily find other, contrasting colors there as well. Look at the reddish Antares and the yellowish-white Altair. And at the top of the line of this summer’s retinue, brilliant orange Arcturus holds forth in solitary splendor high toward the south.AdvertisementAdvertisementEven 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 faint stars tend to appear white to our eyes. However, if we look at them through a binocular or a telescope, their amplified brightness stimulates the cones, which detect their color.Colors by contrastOne of the best ways to see star colors is by contrast. Let’s return to Arcturus for a moment. The classic procedure for locating this star is to follow the arc of the Big Dipper’s handle southeastward. Back in the 1950s, a very popular lecturer at New York’s Hayden Planetarium was Henry M. Neely (1879-1963), who had a favorite ditty for locating Arcturus and another bright star of late spring/early summer: “Follow the arc to Arcturus and speed to Spica.”Spica shines with a distinct bluish tint. Move your eye rapidly back and forth between Arcturus and Spica to see the great difference in their respective orange and blue hues.Spica shines with a distinct blue hue near a blood red moon during a lunar eclipse. | Credit: Nick Chill via Getty ImagesAnother very effective procedure is to observe a double star with contrasting tints. Probably the most colorful double star in the night sky can be found about halfway up in the eastern sky at 11:30 p.m. local daylight time: Albireo in the constellation of Cygnus the Swan, also known as the Northern Cross. Albireo supposedly marks the swan’s beak.AdvertisementAdvertisementA small telescope or even a pair of steadily held binoculars will readily split Albireo into two tiny points of light of beautiful contrasting colors: the brighter one a rich yellowish orange, the other a deep azure blue, both placed very close together. A stunning view will come with a telescope magnifying between 18x and 30x.Stars hot and coolEarlier, we referred to Antares as being reddish, which is how it’s always described. But actually, that isn’t correct. What we regard as “red” stars (which are catalogued as spectral class M) are really yellow-orange and approximately the same color as an old-fashioned incandescent light bulb. Both it and M stars have about the same 3,000 Kelvin color temperature.Our eyes evolved to take advantage of the radiation emitted by the sun, which is an average star as far as temperature and color are concerned. Very hot and cool stars, on the other hand, are strongest in the ultraviolet and infrared ranges, respectively.The bright red star Antares shines beside the Milky Way’s central regions in this image captured from A …
