- Introduction to Earth Science (pressbooks.lib.vt.edu)
Introduction to Earth Science is designed to provide a comprehensive introduction to Earth Science that can be freely accessed online, read offline, printed, or purchased as a print-on-demand book. It is intended for a typical 1000-level university introductory course in the Geosciences.
- Messier 90 (Wikipedia)
Messier 90 (also known as M90 and NGC 4569) is an intermediate spiral galaxy exhibiting a weak inner ring structure about 60 million light-years away in the constellation Virgo. It was discovered by Charles Messier in 1781.