Galileo: seeing stars to magnitude 12

In Sidereus Nuncius (1610), Galileo writes that his telescope allows him to see a further six orders of magnitude. The Greek astronomer Hipparchus devised the magnitude system in about 150 BC. The brightest stars were first nagnitude and the faintest visible to the naked eye sixth magnitude. A first magnitude star emits 100 times the light of a sixth magnitude star. Ptolemy uses this convention in the Almagest.

Galileo's telescope showed stars frommag 7 to mag 12. The light from a mag 12 stars is 10,000 times fainter than mag 1. Galileo described the 7 - 12 mag stars as "so numerous they are almost beyond belief.

Source of this information: follow the links in yesterday's blog