Star light, star bright. Twinkle, twinkle, little star. We are all made of stars...
Stars are one of the most enchanting parts of nature. Some have existed for billions of years; others have had spectacular births and fiery, explosive deaths. Some can be seen with nothing more than an amateur telescope. Others have only revealed themselves to mankind after years of searching and state-of-the-art equipment.
What do you know about stars? What do you want to know? Let's talk about stars, their origins, their characteristics, and why they matter.
What Are Stars? The Definition of Stars
In simple terms, stars are big balls of gas. They're held together by their own gravity and compromised mostly of hydrogen and helium. Nuclear fusion happens at their core, which produces heat and other elements like oxygen, nitrogen, and carbon.
Stars are incredibly hot. The hottest stars in the universe can reach temperatures of 40,000 Kelvin or more, which translates to around 71,540°F. However, even the coldest stars are hotter than us and our planet.
Starlight can take millions and billions of years to travel across the sky. Because of this, we often "see" stars that are no longer there!
How Far Away Are Stars?
Stars are spread throughout the universe, so some are farther from Earth than others.
The closest star is Proxima Centauri. It's 4.24 light-years away, and since a light-year is 5.88 trillion miles, that's almost 25,300,000,000,000 miles.
For a long time, the farthest star was believed to be Icarus, which was nine billion light-years away. However, NASA was able to use the Hubble Space Telescope and find the light of a star even deeper in the cosmos: Earendel. It's measured at 28 billion light-years away, and it's actually long gone. It exploded millions of years ago; it's just taken awhile for the light to reach Earth.
Do Stars Die?
Stars aren't truly alive, so they can't die. However, it's common for people to talk about the "birth" and "death" of stars. You'll also hear phrases like "the life cycle of a star," but rather than a true birth and death, it's referring to their formation and destruction.
Stars die when they run out of fuel. This fuel is the hydrogen that keeps their nuclear fusion going. If you remember, the nuclear core is held together by the star's gravity, so when it isn't able to perform this function anymore, it collapses.
What happens next depends on the size of the star. If it's a large one, its outer layers will explode as it collapses and form a supernova. The supernova will eventually explode as well, creating either a neutron star or a black hole depending on the amount of leftover mass
Smaller stars die less dramatically. They swell, turning into red giants as their hydrogen is used up and their helium fuses in their cores. The outer layers become planetary nebula, and the inner core becomes a white dwarf, a super-heated mass that slowly cools off over the years.
How Are Stars Formed?
Stars are formed from gigantic clouds of gas and dust in space. Their gravity makes them collapse into themselves, heating up as they go, and stars are born from that mass. This is called star formation theory.
What Are Stars Made Of?
Stars are made primarily of hydrogen and helium, but they can contain many elements overall, including carbon, iron, oxygen, and nitrogen. When they die, this material gets ejected back into space, and new stars can be born from the remnants of old ones. It's space recycling!
Why Do Stars Twinkle?
It's more than just a nursery rhyme. Stars really do seem to twinkle in the night sky. So what's really happening up there?
Simply put, stars twinkle because of the way that the Earth's atmosphere bends and refracts light. A common way to conceptualize this is by imagining straight lines and zig-zagged lines. If Earth didn't have an atmosphere, we could see starlight in a straight, direct, and unblinking line. Since the Earth's atmosphere is distorting it, however, starlight appears to travel in a zig-zagged line, which is also what gives it a winking or twinkling appearance.
Distant stars twinkle more than closer ones since their light has even farther to travel before it reaches us.
Different Types of Stars
There are many different types of stars, and people have spent their entire lives studying and categorizing them!
If you just want the basics, however, here's a simple rundown of star classifications:
Blue giants: Blue giants are the biggest and hottest stars in the solar system. On the stellar classification scale with the letters O, B, A, F, G, K, and M, blue giants are typically O and B.
Red dwarves: Red dwarf stars are the most common in the universe. They're smaller and cooler than other types, so they're ranked K and M. Additionally, since they don't overheat to the point of explosion, they live longer. Some astronomers estimate that red dwarves can survive up to 10 trillion years.
Yellow and orange dwarves: These are hotter than red dwarves but colder than blue giants. The Sun is considered a yellow dwarf star. It's rated G: right in the middle of the scale.
Brown dwarves: Brown dwarves are sometimes called "failed stars." They're too cold to generate nuclear fusion like regular stars, and they don't always emit light. They're often mistaken for planets.
In addition to letter and color classifications, there are many, many ways to group stars together according to their characteristics. For example, binary stars are pairs of stars that are gravitationally bound in the same orbit. Protostars are "baby stars" that are still forming. Neutron stars are the remains of gigantic stars that collapsed into themselves and exploded.
What's the Difference Between a Star and a Planet
The subject of stars vs. planets can be a tricky one. However, there are a few key differences that can help you understand the distinction.
The biggest difference between stars and planets is that planets revolve around stars and not the other way around. The Earth revolves around the Sun; the Sun doesn't revolve around the Earth.
Another difference is light. Stars generate and emit their own light thanks to the nuclear fusion going on in their cores. Planets have no fusion, so they don't create light; they only reflect what they receive from their stars.
If you're looking at objects in the night sky and wondering which are stars and which are planets, see if they twinkle. Planets are close enough to Earth that their light doesn't refract when it hits the atmosphere, so they appear steady. Stars are much farther away, so they appear to twinkle.
What's a Shooting Star?
Have you ever made a wish on a shooting star? Have you ever wondered what a shooting star actually is?
You might be surprised to learn that shooting stars aren't really stars. Instead, they're dust and space rocks that are streaking through the sky at extremely high speeds. They move so fast that they pick up a heated glow as they enter the Earth's atmosphere, and that's why they appear to leave a trail behind them.
Another word for shooting stars is meteors. They're also known as falling stars.
How Many Stars Are There in the Entire Universe?
No one knows the exact number of stars in the universe. We lack the technology to count every one, and furthermore, we're still unsure how far and deep the universe actually goes. We're still discovering far-flung stars that lived and died billions of years ago on the edges of the observable universe!
We can make rough estimates of star counts, however, especially for stars close to home. Astronomers estimate that there are roughly 100 billion stars in the Milky Way Galaxy.
What Are the Most Famous Stars?
You're probably familiar with some stars. Even if you aren't an astronomer, they've been subjects of myths, legends, and religions for centuries. They've also entered pop culture as everything from astrological trends to fictional character names.
Though this list is far from comprehensive, here are just a few famous stars:
Polaris: Also known as the North Star, Polaris is commonly thought of as the brightest star in the sky, but it's actually the 45th brightest! It's still quite luminous, however, and since it's close to the north celestial pole, it's been used as a navigational tool for millennia. This is where it gets its reputation as a guiding light.
Sirius: The actual brightest star in the sky is Sirius. Also known as the Dog Star, it's located within the constellation Canis Major or "The Big Dog." Fun fact: Sirius is technically a binary system of two stars, but it appears to the naked eye as a single point in the sky.
Pleiades: Pleiades is more commonly known as the Seven Sisters. Like its name suggests, it's a star cluster with seven bright, visible stars, though there are quite a few more than that if you have the right equipment to view them.
Vega: Vega is a bright blue star that can be seen with the naked eye. It's part of the Lyra constellation, and in ancient times, it was actually considered the North Star.
Betelgeuse: Pronounced "Beetlejuice," this is one of the brightest stars in the Orion constellation. It has a distinctive reddish color, and it's a favorite of amateur stargazers with telescopes.
There's one more famous star that we can't forget: the Sun! Though many schoolchildren mistake it for a planet, it's really a star, and our actual planet Earth depends on it.
Can You Name a Star?
Yes, you can. If you'd like to put a special name in the night sky to join Sirius and Betelgeuse, you can name a star. You can do it for yourself, give it as a gift, or perform it as an act of charity. The possibilities are endless!