Here's why:
* Star Color and Temperature: The color of a star is related to its surface temperature. Red stars are cooler than blue stars. Betelgeuse's reddish color indicates a relatively cool surface temperature of around 3500 Kelvin.
* Wien's Displacement Law: This law states that the peak wavelength of radiation emitted by a blackbody is inversely proportional to its temperature. Cooler objects emit more radiation at longer wavelengths (infrared).
Therefore, Betelgeuse emits a significant amount of infrared radiation, with its peak emission wavelength being somewhere around 900 nanometers. This is longer than the visible spectrum, making it invisible to the human eye.
It's important to note that Betelgeuse also emits radiation across a wide range of wavelengths, including some visible light, which is why we can see it as a red star. However, its peak emission is in the infrared.
