Astronomy was the science dealing with space and stars. An astronomer was an individual who studied astronomy.
When the Master talked about Earth's Sun, the Third Doctor joked about already knowing "a little basic astronomy". (TV: Colony in Space)
Ian Chesterton described Vicki Pallister Earth's sky according to his memories about astronomy. He said that in ancient times, astronomers didn't know the difference between planets and stars. (PROSE: Byzantium!)
In the 19th century, Sir George MacLeish was said to be steeped in astronomy. (TV: Tooth and Claw)
Wilfred Mott was an amateur astronomer. (TV: Partners in Crime)
Henrietta Goodheart, a friend of Mott's, was an astronomer at Greenwich observatory. (PROSE: Beautiful Chaos)
Neverglade was an astronomer who spent some time on Traken; however, he was actually an illusion created by Viola. (PROSE: The Astronomer's Apprentice)