When looking up on a cloudless night, do you notice that stars can sometimes show as different colors? You may even notice yellow, red, orange, and blue stars — not just white.
A star’s color can range from yellow to blue, but you’ll never see a green star in the night sky. And there are reasons behind their coloring. Learn more about why stars shine different colors and the best way to see some of the brightest.
What Determines a Star’s Color?
A star’s surface temperature dictates its color. These colors typically range from hottest to coldest: blue, white, yellow, orange and red, similar to fire. Blue stars, the hottest, usually have a surface temperature range of about 10,000 to 50,000 Kelvin (K).
The sun in our solar system is a yellow star, with a surface temperature of nearly 6,000 K, even though its actual color is white. Because of Earth’s atmosphere, the sun often appears yellow to us.
This isn’t the only thing Earth’s atmosphere disrupts. Have you ever wondered why some stars appear to twinkle? Earth’s atmosphere distorts light that passes through it, and gives some stars a twinkling effect.
Read More: If the Color of the Sun Is White, Then Why Does it Appear Yellow?
Where and When to Spot Colorful Stars
If you want to see a red star, look for Betelgeuse in the constellation Orion. If you want to see blue stars, look for Rigel, also in Orion. Capella, the sixth brightest star seen from Earth, shines a bright yellow in Auriga. And Antares burns a reddish-orange color in the heart of Scorpio.
Before you head outside in the middle of the night to try and spot these stars, there are few things you need to know. The first being is that you need to get away from light pollution if you want the best chance of seeing these stars.
The second, while you may be able to notice stars with the naked eye, having a telescope or binoculars is a great way to enhance your viewing experience.
Lastly, and probably most importantly, you need to know when these stars are going to be in the sky near your location. Depending on the time of year, it may be more difficult to see these stars. According to the BBC, winter skies often offer the brightest stars, so viewing during that season may increase your chances of getting a good glimpse at them.
Why We Don’t See Green Stars
While looking for colorful stars, the one color you won’t see is green. This is related to the way our eyes perceive color.
Human eyes contain light-sensitive cells called rods and cones. Rods are the brightness detectors and are blind to color. Our eyes have three kinds of cones that help us see color: red cones, blue cones, and green cones. When light hits them, each gets triggered by a different amount; red light — say, from a fire truck — really triggers the red cone, but the blue and green cones stay rather calm.
Most objects don’t emit (or reflect) a single color, so the cones are triggered by varying amounts of light. The color orange, for example, triggers the red cones to respond about twice as much as the green cones, but leaves the blue ones unaffected. When the brain receives the signal from the three cones, it says, ‘This must be an orange object.’ If the green cones receive as much light as the red cones, and the blue cones receive no light, we interpret this as yellow. And so on.
Therefore, the only way to see a star as green is for it to emit almost exclusively green light. However, stars are always producing more than one wavelength of light. Any star emitting mostly green will also be emitting a significant amount of red and blue, making the star appear white. Changing the star’s temperature will make it appear slightly orange, yellow, red, or blue, but you just can’t get green. Our eyes simply won’t see it that way.
This article is a republished version of this previously published article.
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