You might think of stars as white pinpricks in the sky. If you have a little more astronomy knowledge, you might think of them as burning red balls of gas like the Sun.
The truth, however, is that stars come in many colors. Some are visible to the naked eyes; others can only be observed by telescope. Together, they make up a diverse and dazzling landscape in the night sky, especially when you stretch your gaze beyond the Milky Way Galaxy and into the greater universe.
Are you ready to learn more about stars and star colors? Let's take off!
What Are Stars?
Without going into scientific detail, stars are large, super-hot balls of gas that are held together by their own gravity. They're "born" from clouds of gas and dust in space, and they "die" when they run out of fuel, which is the hydrogen that they burn in their cores.
Stars emit light, have varying sizes and temperatures, and are found across the known universe. You can learn more here:
Types of stars
When talking about types of stars, there are many different ways to categorize them. You can go by size, color, characteristics, location in space, and more.
One of the most common classification methods is the Morgan-Keenan system. This divides stars by temperature, and it assigns them one of the letters O, B, A, F, G, K, and M. O is the hottest while M is the coldest.
There are also numbers for further dividing stars within their given temperature ranges. 0 is the hottest while 9 is the coolest. An A8 star is hotter than an A9 star, and an A9 star is hotter than an F1 star, and so on.
Now that you understand the Morgan-Keenan system, we can take a look at star colors and how they differ based on their classification.
O-type blue stars are the biggest and hottest in the universe. Also known as "blue giants," they shine with an intense, bluish-white ultraviolet light that can reach temperatures of 25000 - 50000 Kelvin (44540°F - 89540°F). They're also quite rare. In our galaxy, it's estimated that only 0.00003 percent of stars are O-type stars.
B-type stars are still big and hot; they're just slightly less monstrous than O-types. They're rare in terms of frequency, but since they're so luminous, they can be seen in quite a few constellations. A well-known B-type star is Rigel, the brightest star in Orion.
Fun fact: When O-type and B-type stars die, the explosion is so massive that it triggers a supernova, and its remnants become either a neutron star or a black hole.
A-type stars are quite common in the universe. In fact, you can see many of them from your own backyard, including Sirius, Vega, and Altair.
Despite being classified as a "blue" star, many A-type stars are white. They tend to be young, only a few million years old, though astronomers estimate that they can live up to 100 million years. They rotate quickly, emit high levels of infrared radiation, and frequently have planets attached to them.
F-type stars occupy a nebulous category where they can be classified as everything from blue stars to yellow stars to white stars. While often white or blueish-white, they can change colors several times during their life cycles. For example, many F-type stars turn into red giants when they start to fuse helium rather than hydrogen, and after collapsing, they can leave behind a white dwarf at the center of their nebula.
Fun fact: F-type stars can have a mass that's anywhere from 10 - 60 percent greater than the Sun.
YELLOW, RED, AND ORANGE STARS
We're getting into familiar territory now. The Sun is a G-type star.
G-type stars are much cooler than blue stars, which is why their color is different. Their temperature range is usually 5200 to 7500 Kelvin. Despite being called "yellow" stars, their colors can range from a blinding white to a sizzling red. The latter takes place when they start running out of hydrogen.
K-type stars are relatively cool. They're still 3500 – 5000 Kelvin, but when compared to the 25000 - 50000 Kelvin of blue giants, they're positively chilly.
Many K-type stars have an orange, yellow, or red appearance. They're pretty common in the universe and have been subject to lots of study. They're of particular interest to the debate about extraterrestrial life since they emit low levels of radiation and are stable for billions of years. If we ever find aliens, they'll probably be close to a K-type star
M-type stars are usually called "red dwarfs." Comprising 75 percent of stars in our solar neighborhood, they're the most common stars in the night sky, and many can be seen with the naked eye.
Brown dwarfs are a special kind of star. Sometimes called a "failed star" or a "star-planet hybrid," they lack the mass to create nuclear fusion, but they otherwise look and function like a star. They aren't actually brown, however. They range from an orange-red to a deep magenta.
Do Stars Change Color?
Stars can change color over time. It happens during different stages of their life cycle as they create, burn, and eventually run out of hydrogen. They can also change form and color when they explode, leaving behind white cores or black holes in place of their former selves.
Another thing that can affect a star's appearance is their distance. If you've ever wondered why stars twinkle, it's because of their distance from our planet and the way that their light refracts when it hits Earth's atmosphere. Their color can appear different to our eyes for the same reason.
Does Age Impact Star Color?
You've already learned about how temperature can determine the color of a star, but that's not all that can. Age is another important factor in star color.
Since younger stars are burning hydrogen at fast rates, they tend to be hotter, brighter, and bluer than others. Meanwhile, older stars start to cool down as their hydrogen is depleted, and this can turn them red or orange. Darker colors are especially common among big, bloated supergiant stars that are dispersing their heat over a large area.
Fun fact: If you want to hold onto a piece of a star forever, you can name a star and have it officially added to the Star Register database.
To Infinity and Beyond
It's been suggested that 150 billion stars are born every year throughout the universe. This translates to 400 million stars per day! Between their colors, sizes, temperatures, and placements in the universe, the world of stars is definitely an assorted one. If you've ever marveled at its magnificence, you aren't alone.