Gemini, known as the “Heavenly Twins”, is one of the easiest constellations to recognise with over 80 stars visible without a telescope. For astronomy it is one of the most examined constellations due to its diversity. It is rich with various types of stars, galaxies, meteor showers and planetary nebulae.
In Greek mythology, Castor was killed and Pollux asked Zeus to share his immortality with his fallen twin to keep them together. Upon request, Zeus made them into the constellation Gemini. So in the night sky they live forever.
The famous pair Pollux and Castor form the heads of the twins and are among the brightest stars in the sky. Pollux is the brightest in Gemini and Castor actually consists of six stars!
We see one dot with the naked eye but through a telescope we can see Castor A and Castor B, the binary system that makes Castor so bright. A binary system is when two stars orbit one another.
The Pollux system also has a planet in its grasp! The planet is thought to be twice the mass of Jupiter and has an orbital period of 590 days. Quite a short orbital period for such a giant planet. Jupiter’s orbit here takes 12 years.
Gemini actually points away from the Milky Way so there are fewer deep sky objects. The Medusa Nebula is a star forming region within the constellation. The Nebula is around 1500 light years from Earth and much much further away from most other objects within the Gemini constellation group.
The Eskimo Nebula is another star forming region but much further away at 4000 light years away. A challenging object to find with a telescope but certainly worth it when you find it!
Geminga is probably the most interesting object in Gemini. It is a tiny neutron star with a rapid rotation. A neutron star is the core of a massive star that has shed its outer layers in a supernova explosion. Neutron stars are made entirely of neutrons which makes them incredibly dense and heavy. A teaspoon of neutron star would weigh 10 million tons!
The Geminids Meteor shower originated from Gemini and is visible in the sky in mid December. It’s always quite hard to see due to lack of clear nights and the almost certain full or half moon that occurs at this time.