Monday, 9 November 2020

Astrognome 100 Great Stars No 66 Pollux

 

Pollux

Together with Castor, Pollux are the two brightest stars in the zodiacal constellation of Gemini the Twins. In mythology Castor and Pollux were twin boys with the same mother, the immortal Leda, but different fathers. Pollux was immortal while Castor was not. When Castor was killed Pollux was so distraught that he pleaded to be allowed to share his immortality with his brother. His wish was granted and both boys were placed in the sky forever.



Pollux which is labelled by the Greek letter beta is actually brighter than Castor which is labelled with alpha. The Greek letter system was introduced in 1603 by Johannes Bayer. Curiously ancient observers ranked them as the same brightness where today Pollux is clearly the brighter.

Ptolemy in 150, Al Sufi in 960, Ulugh Beigh in 1430 and Tycho Brahe in 1590 ranked them as the same brightness. So too did Bayer in 1603 when he gave Pollux the letter beta. Castor is a mag 1.6 blue star while Pollux is a 1.1 orange star. Either all the ancient astronomers were wrong or one of the stars has changed in brightness the prime suspect would be Pollux due to its colour.


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