In a 2016 study, it was assumed that there were about 2,000 billion stars in the observable universe. Stars are classified and distinguished according to certain characteristics such as volume, mass, magnitude, temperature and more. The temperature is strictly connected to the color that can take on various shades: from red to blue. The photo uploaded above, taken by the Hubble Space Telescope, perfectly shows the different colors that these celestial bodies can assume. As we mentioned earlier, we can classify stars based on their surface temperature:
- Red Stars: These are the coldest stars of all, on average they have a surface temperature of around 3300K with peaks of around 3700K.
- Orange Stars: These stars have a temperature between approximately 3700K and 5000K.
- Yellow Stars: Yellow-colored stars can get around a surface temperature of 6000 K.
- White-Yellow Stars: Stars of this color have a surface temperature that varies between 6000 K and 7500 K.
- White Stars: In this case the surface temperature ranges from 7500K to 10000K.
- Azure Stars: They are among the hottest stars ever. They can reach temperatures of around 33000 K.
- Blue Stars: They are by far the hottest stars in the universe. These stars have surface temperatures above 33,000 K and can even reach 50000 K!
So, why do we see almost all white colored stars in the night sky? It is due to the fact that the human eye is unable to perceive colors when the light is dim. Even if in reality the light of the stars can be very intense, they are still at a very high distance from the Earth: The closest star to us is Proxima Centauri which is 39736 billion km from our solar system!