Double Stars

Colored double stars are one of the most beautiful sights observable through a telescope. These are pairs of stars that appear close together in the sky and show distinctly different colors. The color contrast between the two stars is what makes them spectacular.

The most famous colored double is Albireo in the constellation Cygnus. Through even a small telescope, Albireo resolves into a golden-yellow star and a sapphire-blue companion. The contrast is stunning. Stars can appear in surprising color combinations that seem almost artificial.

The colors are real. They’re caused by the different surface temperatures of the stars. Blue stars are hotter, typically around 10,000 to 30,000 Kelvin. Yellow or orange stars like our sun are cooler, around 5,000 to 6,000 Kelvin. Red stars are the coolest, below 4,000 Kelvin. When you see a blue and gold pair like Albireo, you’re looking at two stars with very different temperatures orbiting each other or just happening to lie in the same line of sight.

Not all double stars are true binary systems. Some are optical doubles - they just happen to appear close together from Earth but are actually at completely different distances. Albireo itself might be an optical double, though there’s still debate about this. True binary stars orbit around their common center of mass, bound together by gravity. These orbital periods can range from hours to thousands of years.

Observing colored doubles doesn’t require expensive equipment. A basic telescope with 60-80 mm aperture is enough to split most famous pairs. Albireo splits easily even at low magnification. Other beautiful colored doubles include Almach in Andromeda (orange and blue), and Ras Algethi in Hercules (orange and green).

The color contrast depends partly on human visual perception. Human vision tends to exaggerate color differences, especially when two contrasting colors appear next to each other. This is called simultaneous contrast. A slightly blue-white star next to a yellow star will appear more intensely blue than it would alone. But the colors are still real - just enhanced by how our eyes work.

The greenish tint some observers report seeing in certain double star companions is particularly interesting. True green stars don’t exist because of how blackbody radiation works. But when a white or blue-white star appears next to an orange or red companion, the eye can perceive it as greenish due to color contrast. It’s a trick of perception, but it makes the view even more beautiful.

Colored double stars remain excellent targets even when the atmosphere is unsteady. Turbulence makes tight binaries harder to split, but the well-separated colored pairs—like Albireo or Almach—still show their beautiful color contrast even in mediocre seeing. Their brightness allows them to cut through light pollution, moonlight, and less-than-perfect transparency.