What is the color of the hottest star? A. blue B. orange C. red D. yellow
The correct answer and explanation is:
Correct Answer: A. blue
The color of a star is directly related to its surface temperature, with blue stars being the hottest. The reason behind this lies in the physics of blackbody radiation, which describes how objects emit electromagnetic radiation based on their temperature.
Stars behave approximately like blackbodies, emitting a spectrum of light. As the temperature of a star increases, the peak of its emitted light shifts to shorter wavelengths. Cooler stars emit most of their light in the red or infrared part of the spectrum, while hotter stars emit more in the blue or ultraviolet region.
Red stars, such as Betelgeuse, are relatively cool with surface temperatures around 3,000 Kelvin. Orange and yellow stars, like Arcturus and our Sun respectively, are hotter, with the Sun’s surface temperature being about 5,800 Kelvin. Blue stars, such as Rigel or Sirius B, are the hottest, often exceeding 10,000 Kelvin and reaching up to 50,000 Kelvin in some extreme cases.
The apparent color seen from Earth is a result of this distribution of emitted wavelengths. A blue star emits a high amount of energy, particularly in the shorter wavelengths of the visible spectrum, which makes it appear blue. The human eye perceives this high-energy output as a bluish hue, indicating the extreme temperatures present on the star’s surface.
This color-temperature relationship allows astronomers to classify stars into spectral types using the Harvard Spectral Classification. These types range from O (blue and hottest) to M (red and coolest). Thus, when observing a blue star, it signifies one of the highest surface temperatures among all stellar types, confirming that blue is the color of the hottest stars in the universe.