Why are blue stars thought to be hotter than red stars?

Blue stars are thought to be hotter than red stars primarily due to their temperatures and the spectral classification of stars. Blue stars emit light at shorter wavelengths, indicating higher energy and temperature, typically ranging from about 10,000 to 50,000 Kelvin. In contrast, red stars have longer wavelengths and lower temperatures, generally between 2,500 and 4,000 Kelvin. This difference in color is a direct result of the stars' temperatures, with hotter stars appearing blue and cooler stars appearing red.