Gemini star map
Copyright: Melbourne Planetarium
Highlights of the tour:
- the twin stars
- a bright open cluster M35
The constellation of Gemini, the Twins, contains the two bright stars Castor and Pollux. In ancient Greek mythology, they were twin brothers, sons of the god Zeus and the mortal woman Leda. They were identical in all aspects except that Pollux had an immortal soul, while Castor was mortal. When Castor died Pollux pleaded with the gods for the brothers to be reunited, and they were placed in the sky together. Gemini is visible in our northern summer skies and is one of the constellations of the Zodiac, in which we find the Sun, Moon and planets.
Stop 1
Castor and Pollux easily fit into the same field of view with binoculars. Though their mythical namesakes were said to be absolutely identical, these two stars are not. Pollux is the brighter of the two and has a clear orange colour, while Castor is white. Pollux is 36 light-years away, while Castor is 46 light-years. Castor is also a multiple star system, though it appears to be a single star through binoculars. Through a small telescope it can be seen as two stars, while a more powerful instrument reveals a third companion. Furthermore, each of these stars has been found to be a binary star system, so Castor actually consists of six stars.
Stop 2
Here at the edge of the constellation is the open cluster M35. It is one of the brightest open clusters and is visible to the unaided eye on dark nights. With binoculars it appears as a large misty spot surrounded by a rich star field. The cluster itself is only partly resolved into individual stars with binoculars. M35 contains 120 stars and is half a degree across.