Why do stars have different colors?

The diverse colors of stars in the night sky offer a captivating spectacle, with each hue revealing crucial information about a star's temperature and composition. Brighter stars, in particular, showcase a more pronounced range of colors, allowing observers to appreciate the celestial palette.

Notable examples include Vega, which shines with a brilliant bluish-white light, and Antares, appearing reddish. Altair presents a yellowish-white glow, while Arcturus is distinctly orange. This variety creates a stunning spectrum across the constellations, though fainter stars often appear white to the human eye because our photoreceptors, the cones, are less sensitive to dim light.

A striking illustration of color contrast is found in Albireo, a double star in the constellation Cygnus. Even with binoculars, Albireo appears as two distinct points of light: one a vibrant yellow-orange and the other a deep blue. This pairing offers a particularly mesmerizing display.

The underlying physics of stellar color relates to black-body radiation. A star's temperature dictates the peak wavelength of the light it emits. Hotter stars radiate more energy and their spectral peak shifts towards the blue end of the spectrum, while cooler stars emit less energy, with their peak emission in the red or infrared parts of the spectrum. Our Sun, considered an average star, emits light across a spectrum to which human eyes are adapted.