Why blue stars are generally hotter than red stars
A star's surface temperature affects the distribution of light it emits. Hotter stars emit a larger share at shorter wavelengths and often appear blue-white, while cooler stars can appear orange or red. Colour is a temperature clue, but apparent brightness also depends on size, distance and intervening material.
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Colour reflects a broad spectrum
Stars emit light across many wavelengths rather than producing only the colour visible to our eyes. Their surface temperatures strongly influence how that energy is distributed.
As temperature rises, the peak of the thermal spectrum shifts towards shorter wavelengths. This helps make hot stars look blue-white and cooler stars look reddish.
Red does not mean a star is barely warm. Even a cool stellar surface is extremely hot by everyday standards.
- Temperature influences the spectral distribution.
- Size affects the total energy emitted.
- Distance affects how bright the star appears to us.
Dust between a star and the observer can also redden its light, so astronomers use more than a casual colour impression to determine stellar properties. A bright-looking red star need not be hotter than a faint-looking blue one.