How far away is the sun?
In which one of Darwin's correspondents compares Darwin's famous moth prediction with the prediction of the orbit of the planet Neptune.
400 years ago today, on 26th July, 1609, the early English scientist Thomas Harriot pointed his new-fangled telescope at the moon and made a drawing.
'Popular Scientific Recreations, Profusely Illustrated' on the subject of Mars.
Amazing space photo.