Draco

Draco is a constellation in the far northern sky, its name Latin for dragon. It was one of the 48 constellations listed by the 2nd century Greek astronomer Ptolemy and remains one of the 88 modern constellations today. The north pole of the ecliptic lies in Draco, and the constellation is circumpolar from northern latitudes, meaning it never sets and can be seen at any time of year. Its brightest star is Gamma Draconis, an orange giant of magnitude 2.2 located 148 light-years from Earth, also known by its traditional name Etamin or Eltanin. In 1728, James Bradley discovered the aberration of starlight while observing this star. Another notable star is Thuban, or Alpha Draconis, a blue-white giant that served as the northern pole star from 3942 BC to 1793 BC; the ancient Egyptians aligned the entrance passages of their pyramids so that Thuban would be visible at night. Due to precession, it will again become the pole star around the year AD 21000. Beta Draconis, called Rastaban, is a yellow giant of magnitude 2.8, and its name, like Thuban’s, means "head of the serpent." Draco contains numerous double and binary stars, including Eta Draconis, a double with a yellow primary and white secondary, and Mu Draconis, a binary with two white components orbiting each other every 670 years. The constellation also features the red Mira-type variable star R Draconis, discovered in 1876, which varies between magnitudes 7.6 and 12.4 over roughly eight months. Among its deep-sky objects is the Cat’s Eye Nebula, a planetary nebula discovered by William Herschel in 1786, named for its complex shape as seen by the Hubble Space Telescope. Draco also hosts several faint galaxies, including the Draco Dwarf Galaxy, one of the least luminous known, discovered in 1954.