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Explore Companion Castor, Secret Board, and more!

The star Castor in Gemini. You can resolve it into three stars in a small telescope, but each of the stars has a companion. Castor is really a sextuple star system. (The diagram is not to scale.)

Castor, which is actually a sextuple star system, can be seen as is a fine, close double star in small telescopes. (Credit: Damian Peach) Mona Evans, "Gemini - the Celestial Twins"

Procyon, the seventh brightest star in the sky and one of the vertices of the Winter Triangle. It's one of our nearest neighbors at just over 11 light years away in the constellation Canis Minor. Procyon is a binary star system, composed of a white main sequence star and a white dwarf star.

Arcturus – Sun comparison. (Illustration – Bob King) The Sun looks very small compared to red giant Arcturus. Mona Evans, "How Big Are the Biggest Stars"

Quintuplet Cluster. It's most famous star is the Pistol star, the most luminous known star in the Galaxy. On the left is the Hubble image from 1999. On the right is a new one from 2015 - quite a difference in resolving power for the fabulous space telescope.

The nearest stars, their distances in light-years, spectral types and known planets. Only 9 of the stars within 15 light years can be seen with the unaided eye from Earth. (Credit: Karl Tate / Source: NASA)

Open star cluster Messier 50 in the constellation Monceros. (Credit: Canada-France-Hawaii Telescope / Coelum) Mona Evans "Monoceros the Unicorn"

Size comparison of Solar System planets, the Sun, and other stars. (Credit: Dave Jarvis)