Earth was very inhospitable for life for quite some time. In the future, it could become barren again. What’s to say that Venus wasn’t once harboring life? We don’t know anywhere near enough of its geology to even guess that.
The science which treats of the celestial bodies, of their magnitudes, motions, distances, periods of revolution, eclipses, constitution, physical condition, and of the causes of their various phenomena.
A treatise on, or text-book of, the science.
From the GNU version of the Collaborative International Dictionary of English.