Are There Green Stars? Navigating the Colors of Space

Looking at any image from a telescope, you immediately notice a universe full of color. The purple and blue swirls of galaxies or the flaming red bursts from suns are iconic against the blackness of space. All colors seem possible in space. So, are there green stars? Pictures would suggest this is a possibility, but there is more to this phenomenon than meets the eye, especially if you’re not an astronomy student.

Are There Green Stars?

No. Stars take many colors, but there are no green stars in recorded history, and there likely never will be. Some immensely strange occurrences would have to happen to make this manifest. Why is this so hard to imagine?

Stars’ colors are determined, mostly, by temperature. The thermal radiation it emits solidifies its color. If the star gets hotter, things could change as the light surrounding it radiates at different frequencies. Though it seems like reverse logic, hotter stars appear white or blue, much like the hottest flames for candles. Cooler temperatures are warmer colors, like red.

Human eyes prohibit stars from appearing green. Light is possible in many colors, but the spectrum emanating from a star is vast. Eyes see a collection of them simultaneously and the strongest wins out. Dominant colors across the spectrum — those that are hotter and burning brighter — will carry more weight than colors in cooler temperatures. Therefore, the hot, blue frequencies will overpower the cooler red ones buried in there somewhere. 

Any colors in the middle of the spectrum get lost in translation to human eyes. Green never stands a chance to cut through and be the main attraction in space. This is why all stars are red, blue, or white. Some can even appear orange or yellow. Light pollution could also affect our perception of how these colors come across.

How Do You Classify Stars?

Experts place stars in classes, using references like the Hertzsprung-Russell diagrams. These show metrics like luminosity and surface temperature, which point to the color the numbers correlate with. The classes are as follows:

• O: Blue in color with a temperature of 30,000 K or more.
• B: Blue-white in color with a temperature of 10,000-30,000 K.
• A: White in color with a temperature of 7,500-10,000 K.
• F: Yellow-white in color with a temperature of 6,000-7,500 K.
• G: Yellow in color with a temperature of 5,200-7,500 K.
• K: Orange in color with a temperature of 3,700-5,200 K.
• M: Red in color with a temperature of 2,400-3,700 K.

There is no temperature region that can produce green as the primary color for a star. You may notice other colors are omitted. 

What About Green Galaxies?

This is a different story. Green galaxies could make any curious mind forget about the prospect of a green star. Photos from the University of Alabama, Tuscaloosa of NGC 5972 show a galaxy surrounded in an almost nuclear-green shade — why? Doubly ionized oxygen and temperatures of 50,000 K achieve this effect, creating one of the rarest pigments in space. Some of them don’t even have stars within them.

Most people actually see this phenomenon on Earth without needing a telescope. The famous Northern Lights, or the Aurora Borealis, sport a green coat much like these rare galaxies for the same reason.

Some other celestial bodies, like comets and nebulae, can also have a greenish tint because of those oxygen emissions. However, this is not what happens around stars, so the effect is not likely to happen. If a star looks green, it’s likely a trick of the eye.

Frequently Asked Questions About Star Colors

Now that you’ve uncovered the simple reason why green stars don’t exist — everyone can blame the rods and cones in the eyes — unearth a few other tidbits about their mystique.

What Is the Rarest Color of Star?

If it isn’t green, what is it? Blue stars are the most uncommon. As mentioned, the color spectrum surrounding a star is full of colors. However, when astronomers classify them, they use the “peak” color as the characteristic for categorization. Blue stars indicate the hottest temperatures, making them the hardest to find in the night sky.

What About Purple Stars?

There are no purple stars for a similar reason there are no green stars. The way humans perceive color would not be able to pick up purple distinctly enough from its surrounding colors to identify it as such. It is also not part of the Hertzsprung-Russell, which also omits pink. The closest you will get to seeing purple is a saturated blue.

Isn’t Beta Librae Green?

There is a famous star named Zubeneschamali, or Beta Librae. Many call its color green, though this is hotly debated. It is part of the Libra constellation, which has been viewed by astronomers old and contemporary. Older researchers claimed it was green, which has translated to the modern age. However, many combat this by correcting this fact, suggesting it is blue.

A Dark Sky Full of Color

Are there green stars? You may wish there could be, as it would make the night sky even more mysterious and interesting. However, physics and our eyes make it impossible for it to happen. The fact there are no green stars should only make humanity even more curious about the strange textures and colors we see in space. You never know what it could indicate or unlock about the unknown.