The universe contains billions of stars scattered throughout space. Each one has unique characteristics, and among those characteristics is color. Throughout human history, people have wondered what color stars are.
For this reason, in this article we are going to tell you what color the stars are, how you can tell and how it affects whether they have one color or another.
What color are the stars
In the sky, we can find thousands of stars shining, each with a different brightness depending on its size, age, and distance from us. But if we look at them closely or through a telescope, we see that stars can also have different colors or shades, from red to blue. We find bluer stars and redder stars. Such is the case of the bright star Antares, whose name aptly means "Rival of Mars," as it rivals the intense colors of the red planet.
The color of stars depends primarily on the temperature of their surfaces. Thus, although it may seem contradictory, blue stars are the hottest and red stars are the coolest (or rather, the least hot). We can easily understand this apparent contradiction if we recall the spectrum that almost all of us learned about in school as children. According to the electromagnetic spectrum, ultraviolet light is much stronger than infrared light. Therefore, blue implies more intense and energetic radiation and, consequently, corresponds to higher temperatures.
So, in astronomy, stars change color according to their temperature and age. In the sky, we find blue and white stars, or orange and red stars. For example, the Blue Star Bellatrix has a temperature of over 25.000 Kelvin. Reddish stars like Betelgeuse reach temperatures of only 2000 K. If you want to learn more about the types of stars, you can consult our article on star types or on stars larger than the Sun. It's also interesting to know what color the Sun is, and for that, you can check out this article on what color the Sun is.
Classification of stars by color
In astronomy, stars are divided into seven different classes based on their color and size. These categories are represented by letters and further subdivided by numbers. For example, the youngest stars (smallest, hottest) are blue and are classified as O-type stars. On the other hand, the oldest stars (largest, coolest) are classified as M-type stars. Our Sun is the size of an intermediate-mass star and has a yellowish tint. It has a surface temperature of around 5000–6000 Kelvin and is considered a G2 star. If you want to learn more about the color of our solar system, check out the article on [missing information]. As it ages, the Sun becomes larger and cooler, while also becoming redder. But that's still billions of years away.
The color of the stars indicates their age
Furthermore, the color of stars gives us an idea of ​​their age. As a result, younger stars have a bluer hue, while older stars have a reddish hue. This is because the younger the star, the more energy it produces and the higher the temperature it reaches. Conversely, as stars age, they produce less energy and cool down, becoming redder. However, this relationship between age and temperature is not universal because it depends on the star's size. If a star is very massive, it will consume fuel faster and turn redder in less time. Conversely, less massive stars "live" longer and take longer to lose their blue color.
In some cases, we observe stars that are very close to each other and have very contrasting colors. This is the case with the albino star in Cygnus. To the naked eye, Albireo looks like an ordinary star. But with a telescope or binoculars, we will see it as a single star of a very different color. The brighter star is yellow (Albireo A), and its companion is blue (Albireo B). It is undoubtedly one of the most beautiful and easiest double stars to see. To learn more about these fascinating stars, you can read our article on double stars or on how stars form.
blink or wink
Sirius is one of the brightest stars in the Northern Hemisphere and is easily visible in winter. When Sirius is very close to the horizon, it appears to twinkle in all colors, like party lights. This phenomenon isn't caused by a star at all, but by something much closer: our atmosphere . The different layers of air at varying temperatures in our atmosphere mean that the starlight doesn't travel in a straight line, but is refracted repeatedly as it travels through our atmosphere. This is known to amateur astronomers as atmospheric turbulence, which makes stars appear to twinkle.
You've undoubtedly noticed the wild wobble of the stars, that constant "twinking" or "swinging." You'll also notice that this twinkling becomes more intense as we approach the horizon. This is because the closer a star is to the horizon, the more of the atmosphere its light has to pass through to reach us, and therefore, the more it is affected by atmospheric turbulence. In the case of Sirius, which is very bright, the effect is even more pronounced. Thus, on erratic nights near the horizon, this turbulence makes the star appear to be moving, and we see it as if it were casting different shadows. This is a natural, everyday effect unrelated to stars, and it also affects the quality of observations and astrophotography. To better understand why stars twinkle, check out our article on why stars twinkle or discover more about the color of the universe.
How long do the stars shine?
Stars can shine for billions of years. But nothing lasts forever. The fuel they have for nuclear reactions is limited and is running out. When there is no more hydrogen to burn, helium fusion takes over, but unlike hydrogen, it is much more energetic. This causes the star to expand to thousands of times its original size at the end of its life, becoming a giant. The expansion also causes them to lose heat at their surface and have to distribute more energy over a larger area, so they turn red. The exception is these red giant stars, known as the giant star belt.
Red giants don't last long and quickly consume what little fuel they have left. When this happens, the nuclear reactions within the star are exhausted, failing to sustain it. Gravity pulls on its entire surface, shrinking the star until it becomes a dwarf. Due to this brutal compression, energy becomes concentrated, and the surface temperature rises, essentially turning it white. The corpse of a star is a white dwarf. These stellar remnants are another exception to the rule for main-sequence stars.
