What is the color of the coolest star?

What Color Are the Really Cool Stars? (Hint: It’s Not Blue!)

Ever looked up at the night sky and noticed how some stars seem a bit… different? They’re not all twinkling with the same white light. Some have a definite color, and that color tells a story about how hot (or not!) they are. Turns out, the coolest stars aren’t the icy blue giants you might imagine. They’re red. Deep, somewhat dull red, in fact. Think of them as the embers in a cosmic fireplace.

These reddish stars are called red dwarfs, and they’re the workhorses of the Milky Way. In fact, they’re the most common type of star out there. Now, when I say “dwarf,” don’t picture something tiny and insignificant. They’re smaller than our Sun, sure, maybe only 7.5% to 50% of its mass. But what they lack in size, they make up for in longevity.

See, red dwarfs burn their fuel incredibly slowly. Their cores are cooler, and nuclear fusion happens at a snail’s pace. This slow burn means they can potentially live for trillions of years – talk about a long-term investment! Their surface temperatures usually range from about 2,000 to 3,500 Kelvin. To put that in perspective, our Sun blazes away at around 5,500 degrees Celsius.

So, why red? Well, it all comes down to temperature and a handy thing called Wien’s Law. Basically, hotter objects glow with shorter wavelengths, which we see as blue or white. Cooler objects? They emit longer wavelengths, which show up as red or orange. Red dwarfs pump out most of their energy in the red and infrared parts of the spectrum. While they do give off other colors, the red is dominant, giving them that signature hue.

You’ve probably heard of Proxima Centauri, right? It’s the closest star to our Sun! Guess what? It’s a red dwarf. You can’t see it with the naked eye, though, because it’s pretty faint. Another cool example is TRAPPIST-1. It’s a red dwarf famous for having seven Earth-sized planets orbiting it! Imagine the sunsets on those planets – probably a lot of red!

Now, here’s a little wrinkle: not all red dwarfs are the same shade of red. Some might lean more towards orange, depending on their exact temperature and what they’re made of. Plus, there’s this thing called interstellar reddening. Basically, dust in space can scatter blue light, making stars look redder than they really are. It’s like looking at a sunset through a hazy sky – everything takes on a reddish tint. So, next time you’re stargazing, keep an eye out for those faint, reddish embers. They might just be some of the coolest – and longest-lived – stars in our galaxy.