Why Antares Looks So Red
Antares is a red supergiant, a star in a late stage of its life whose outer layers have expanded enormously. Those layers are cooler than the surfaces of hotter stars such as the Sun. Cooler stars emit a larger share of their visible light toward the red end of the spectrum, giving Antares its distinctive color.
The redness is not a cloud or a glow surrounding the star. It is the color of the starlight itself, traveling across space before it reaches our eyes. Antares also gives off much of its energy as infrared light, which human vision cannot see.
A Star That Outgrew Its Original Shape
As a massive star uses up fuel in its core, its structure changes and its outer layers swell. Antares has grown so large that, if it were placed where the Sun is, its surface would extend beyond the orbit of Mars. Its great size helps make it conspicuous despite its distance: it is one of the brightest stars in the constellation Scorpius.
That combination—a vast, relatively cool surface and a bright point of light against a dark sky—makes Antares’ red color easy to notice. The same hue that can seem startling to the naked eye is a visible clue to the star’s physical state.
