How to use "astronomer" in a sentence

Towards midnight on 12 August, one astronomer noticed a great cloud of hot gas on the surface of the planet

I do not think I would have known anything about it myself if I had not met Ogilvy, the well-known astronomer

Denning, our greatest astronomer, said that the height of its first appearance was about one hundred and fifty kilometres

One astronomer has given excellent reasons for supposing that the Martians have actually landed on Venus

Emily is an astronomer - a scientist who studies the stars in the sky