Stars, the luminous points of light in our night sky, display a surprising array of colors, from fiery reds to brilliant blues. These varied hues convey important information about a star’s characteristics, allowing astronomers to understand more about these distant celestial objects.
The Science of Star Color and Temperature
A star’s color is directly linked to its surface temperature. Hotter stars emit light at shorter, bluer wavelengths, while cooler stars emit light at longer, redder wavelengths. As an object heats up, the peak wavelength of the light it emits shifts from red, through orange, yellow, and white, to blue.
The hotter a star’s surface, the more energy it radiates, with a significant portion concentrated in the bluer part of visible light. Conversely, a cooler star radiates less energy, and its peak emission falls within the red or infrared portions of the spectrum. This relationship means that color serves as a reliable indicator of a star’s surface temperature. For instance, a star around 40,000 Kelvin appears blue, while one at 3,000 Kelvin appears red.
Identifying the Coolest Stars by Color
Based on the relationship between color and temperature, the coolest stars appear red or orange. Red stars, such as red dwarfs, typically have surface temperatures ranging from 2,400 Kelvin to 3,900 Kelvin. Larger, evolved red giant and supergiant stars also exhibit these cool temperatures, despite their immense size.
Prominent examples of red stars include Betelgeuse and Antares. Betelgeuse, a red supergiant in the constellation Orion, exhibits an orange-red hue and has a surface temperature of 3,300 to 3,700 Kelvin. Antares, another red supergiant in the constellation Scorpius, appears distinctly reddish with a surface temperature of 3,400 to 3,660 Kelvin. These stars radiate most of their visible light at the longer, red end of the spectrum, signifying their lower surface temperatures.
Orange stars represent the next step up in temperature from red stars, with surface temperatures typically between 3,500 Kelvin and 5,200 Kelvin. Aldebaran, the brightest star in the constellation Taurus, is a notable orange giant. Its surface temperature is 3,900 Kelvin, giving it a clear orange appearance. Both red and orange colors indicate stars significantly cooler than our Sun, which has a yellowish-white appearance and a surface temperature of 5,778 Kelvin.