A star that looks blue has its peak wavelength in the ultraviolet part of the electromagnetic spectrum.

Here's why:

* Wien's Displacement Law: This law states that the peak wavelength of radiation emitted by a blackbody (like a star) is inversely proportional to its temperature.

* Hotter Stars, Shorter Wavelengths: Blue stars are much hotter than red stars. Since hotter objects emit radiation with shorter wavelengths, a blue star's peak wavelength will be in the ultraviolet region, even though our eyes perceive it as blue.

While we can't see ultraviolet light, the portion of the star's radiation that falls within the visible spectrum is primarily in the blue range, giving it its characteristic color.