What Are Stars? 5 Surprising Facts About Stars | Almanac.com

Discover 5 Surprising Facts About Stars (That You Probably Don't Know!)

Star Cluster NGC 290

Star Cluster NGC 290, October 30, 2019

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All About Stars, What They're Made of, And Their Real Color

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If you’re a stargazer, discover the surprising world of stars. What are stars made of, and what color are they, really? Bob Berman shares five surprising facts about stars. How many do you know?

As an almanac, we often share seasonal star facts. Like, if it’s summer and a single bright star hovers directly overhead, it’s Vega, which, despite its fame, is rarely correctly pronounced as VEE-ga. Endless pleasure and exploration await those who, throughout the ages, take the time to learn the stars.

But for now, let’s simplify by rewinding to the starry ABCs.

Twinkle, twinkle, little star,
How I wonder what you are.

That nursery rhyme asks a reasonable and ancient question. So, okay, what are they?

What is a Star?

Today, we know that stars are big glowing balls of hot gas, mostly made of hydrogen with some helium, as well as small amounts of other elements. Our Sun is a star—one of approximately 200 billion trillion stars in the universe!

But when you look up, what do you see? Stars appear as nocturnal points of light, twinkling in the night sky

Here’s where it gets interesting. Stars have no size, and they are unique in that way. Even if you used the world’s largest telescope with the highest possible magnification, every star would remain just a dot with no diameter or width!

A star (our own Sun), as captured by NASA’s Solar Dynamics Observatory.

Imagine the frustration of early civilizations trying to figure out Nature, like the ancient Greeks. Their ranks included some amazingly keen minds. One of them, Eratosthenes, was put in charge of the world’s greatest repository of knowledge, the Library of Alexandria. He was smart. He correctly figured out not only that Earth is a ball but nailed its true size to within a 3% accuracy, and without ever setting foot outside of Egypt! Yet even he didn’t know the slightest about the distance to the stars, why they shine, and all the other stuff everyone was dying to know.

By the 17th century, we’d figured out that stars are all very far away.

What Does a Star Look Like?

Right now, hold up a finger and alternately blink one eye and then the other. Watch how your finger’s location jumps relative to the background wall with each eye blink. What if we could observe a star from one location and then see it from another place? Would it shift position against more distant stars? 

Several Renaissance astronomers actually did this. They figured out that as we orbit the Sun, we observe a relatively nearby star from one location in January and then see it from a different place in July. Measuring its shift in the sky, called parallax, and knowing Earth’s changing mileage (twice the Sun’s distance from us) during those six months lets simple trigonometry nail its distance.

Which was still off-the-charts super-distant. That’s why in 1835, the French philosopher Auguste Compte said he was sure, “We will never know the composition of the stars!” It really seemed the old “how I wonder what you are” inquiry was a futile yearning for knowledge forever hidden from us. Compte’s pessimism made sense, since at such stupendous distances we’d never be able to sample star material and analyze it.

But he was wrong! In just a few years, physicists figured out that things that glow, like a blacksmith’s red-hot iron or the Sun and stars, give off light whose complex color-pattern when seen through a special prism reveal their exact chemical composition.

A monster star, AG Carinae, surrounded by a glowing halo and gas and dust. Credit: NASA/ESA

What are Stars Made of?

Many millions of years ago, only a few elements existed, including hydrogen and helium. The first stars were mainly made of these two elements.

When the first stars died, the matter exploded into space. This matter created new and different combinations of elements, including new stars, asteroids, and planets—plus water and life on Earth.

Today, “baby stars” are born in a star nursery made of massive clouds of gas and dust. These clouds are very cold, causing clumps to form. As the mass grows, gravitational force strengthens, causing clumps to collapse. When this happens, friction causes the material to heat up, which eventually leads to batches of baby stars!

A star nursery captured by the James Webb Space Telescope. Credit: NASA

Get this. Stars do not contain any substance already found on Earth. Nearly all the elements in our body were made in a star that died and went supernova! Learn about supernovas, which are super cool. Without stars, we humans wouldn’t be here at all. 

The Crab Nebula is what’s left of a massive star that went supernova in 1054. Credit: NASA

5 Surprising Facts About Stars

Stars are glittering cosmic furnaces that make us ponder the mysteries of the universe and gaze up in awe. 

1. Nearly all stars appear white to our eyes, but they come in a rainbow of hidden colors.

Many stars are red, blue, green, orange, etc. But because they are light years away from us, our eye is hardly ever able to distinguish the color. White is what our eyes and brains make us perceive if light contains red, green, and blue, light’s primary colors. If a star emits an excess of some color, like blue, it’ll look bluish-white like Vega—in a word, pastel. If they have any noticeable tint, it can be any color except green. Our eyes can not detect green stars.

Read more in my post, “Stars come in every color except green.”

2. Stars do not “burn fuel” to stay hot; they are exploding in a nuclear reaction

For centuries, we still couldn’t fathom why stars shine. By the 19th century, we’d figured out that the nearest star is the Sun, whose closeness made it the easiest to study. Then, almost exactly a century ago, in 1920, the British physicist Arthur Eddington finally revealed how the stars shine. 

It wasn’t intuitive. After all, if a ball of fuel like coal that weighed as much as the Sun (the same mass as 330,000 planet Earths) it would burn out after just 2,000 years. So the Sun and stars just can’t be burning the way normal fire operates.

Eddington had figured out nuclear fusion. In any sun’s core, there is a big glowing ball made of hot gas, mainly hydrogen and helium. The intense temperature and pressure squeeze the hydrogen atoms into each other so that four of them produce one atom of helium. 

This process, nuclear fusion, releases energy, which heats the star and prevents it from further collapsing under the force of gravity. Each pencil-eraser-sized bit of the Sun creates the same power that all the electric lights in the U.S. consume in a week.

3. The dazzling surface of the Sun that we see is not generating light.

The Sun we see is only its 200-mile-thin surface layer where light is escaping! The Sun’s energy comes solely from its core, a small ball in the exact center that’s just 1/50th of the Sun’s size. Each second, this core releases the energy of 96 billion one-megaton H-bombs.

What exactly comes out of the Sun and stars? Half the solar emissions are visible light, the same colors as a rainbow. No star in the universe emits any hue other than those. Almost the entire second half of its energy output is infrared, which our eyes cannot see, but our skin senses as heat. The few remaining percent of the Sun’s emissions are in the form of powerful ultraviolet rays. This UV is what gives us sunburns.

4. Our Sun is not yellow.

Our Sun’s strongest emission is green light, so our eyes perceive green more easily than the others. In the dimming evening twilight, when roses and violets have faded to shades of gray, green grass alone retains its color.

Textbooks state that the Sun is a “yellow dwarf star.” This is strange and incorrect.  While a setting Sun can appear yellow, orange, or even red, a high-up Sun in clean, dry air is a shade of white. Astronauts also report the Sun to appear as white as snow.  To find out for yourself, you can try a very cool experiment.

First, be aware that our blue sky adopts that color because the Sun’s shorter light waves (blue and violet) bounce around among air molecules six times more readily than longer solar waves like reds. This removes some blue light from the Sun’s full-spectrum emissions, leaving its disk with an apparent excess of the other primary colors, red and green.

Interestingly enough, the combination of red and green light creates the sensation of yellow in the human eye. So, the formation of our blue sky is the same process that gives the Sun a slight lemony tint. (Astronauts above the atmosphere see the Sun without any of this blue-removal process). 

To discover the Sun’s true color for yourself, on a clear day in winter, look at a snowy field. The sun’s slight yellowish whiteness is illuminating it and also the blue sky. So all those Sun emissions re-mix on the ground. The snowy surface reflects both the blue sky and the sun’s direct rays to your eyes. The omelet’s eggs are now unscrambled. Result: On a clear day, the snow’s color shows you the Sun’s true appearance as seen by astronauts in space. And it’s neutral white.

This is true of all other stars, too. However, stars with cooler surfaces, like Orion’s famous Betelgeuse, radiate an excess of red light, which makes them look pastel reddish-yellow. Unusually hot stars, like Leo’s and Virgo’s main stars Regulus and Spica, emit extra blue that gives them a diamond blue-white appearance.

5.  Stars do not really twinkle.

The immense starry distance that makes stars mere points means their slim streams of arriving light are easily bent or refracted by dense, colder layers of our atmosphere. 

The lower a star is, the more distorting air layers it must penetrate, making its star point zigzag one way and quickly zag another. 

Result: Twinkling. Yes, it’s just a result of Earth’s atmosphere. If you were above the Earth, the stars do not twinkle.

Planets also look like points to the eye but are actually disks with plenty of size visible through telescopes, which lets them resist such atmospheric mistreatment. 

Read more in my post, “Why do stars twinkle at night.

Now we know what they’re made of, why they shine, why they look the way they do, and how we know their distance. We’ve come a long way since “Twinkle, twinkle….”

About The Author

Bob Berman

Bob Berman, astronomer editor for The Old Farmer’s Almanac, covers everything under the Sun (and Moon)! Bob is the world’s most widely read astronomer and has written ten popular books. Read More from Bob Berman

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