Today’s Question
Why do some stars in the night sky look blue and others look red?
Hyeongseop was gazing at the stars scattered outside Byeol-maru’s window when he noticed something odd. Usually he just thought of them all as plain white twinkles, but today the colors seemed unusually vivid. Some stars glowed white, some glowed red, and others shimmered with a faint blue tint.
“Byeoli, the stars are all different colors. I thought stars were all just white or yellow.”
“A star’s color actually shows how hot it is. It’s a bit like building a fire, when it first starts it glows red, then as it gets hotter it turns white, and if it gets hot enough, it can even glow blue.”
“So blue stars are the hottest ones?”
“Exactly. Blue stars have the highest surface temperature, followed by white, then yellow, then orange, with red stars sitting at the relatively coolest end. Our Sun is a yellow star, right in the middle of that temperature range.”
Hyeongseop looked out at the stars again. Moments ago he’d seen them as nothing but similar twinkling dots, but now each color seemed to carry its own story.
“Then why is our Sun yellow?”
“The Sun isn’t quite as hot as blue or white stars, but it’s not as cool as red ones either. Actually, the Sun’s own light is almost white. As it passes through Earth’s thick layer of air, some of the blue light gets scattered off in every direction, leaving more yellow light to reach our eyes, which is why it looks yellow to us.”
“So the same air that makes the aurora also affects how we see the Sun’s color?”
“Exactly right, that same layer of air does a lot of jobs. It blocks the solar wind, colors the sky, and even filters starlight a little, all at once.”
“But why does temperature change the color at all?”
“Hotter objects give off shorter, stronger wavelengths of light. Blue light has a short wavelength, so it shows up strongly from very hot stars, while red light has a longer wavelength, standing out more from relatively cooler stars.”
“So we can actually tell how hot a star is just by its color?”
“Exactly. Scientists study the color of starlight to estimate a star’s temperature, age, and even how much longer it might keep shining. A single color carries hints about that star’s whole life story.”
“Do the hottest blue stars just stay hot like that forever?”
“Actually, no, blue stars tend to have surprisingly short lives. They burn through their fuel far too hot and far too fast. Red stars, on the other hand, burn cooler but can shine steadily for a much, much longer time. A bright, fast, dazzling life and a quiet, long-lasting one, both fill up the universe in their own way.”
Hyeongseop stared for a long while at one glowing red star. Maybe, he thought, it had once burned hot and young, and had since cooled with age. And somewhere far off, that shimmering blue star was probably living through its hottest, most dazzling days right now. The night sky, Hyeongseop decided, was really just a huge village filled with stars of every age, all living together.
“A star’s color reveals its surface temperature, blue is hottest and red is coolest, and the hottest blue stars actually burn out the fastest.”
How Much Did You Guess Right? (Mixed True/False)
- (True/False) Blue stars are cooler than red stars.
- What color star is our Sun?
- (True/False) The Sun looks yellow because it is yellow light itself.
- What can star color tell scientists?
- (True/False) Blue stars have shorter lifespans than red stars.
(Answers: 1. False, blue stars are hotter. 2. Yellow. 3. False, Earth’s air scatters blue light so it looks yellow. 4. Temperature, age, and lifespan. 5. True.)
Curious why stars twinkle but planets don’t? Read Why Do Stars Twinkle But Planets Don’t? And for the stardust inside you, see There’s a Star Inside You.
답글 남기기