When Did the asteroids Become Minor Planets?
- Discusses the discovery of the first asteroids, their designation as planets, and their reclassification.
- http://aa.usno.navy.mil/hilton/AsteroidHistory/minorplanets.html

The Struggles to Find the Ninth Planet
- A paper by Clyde Tombaugh relating his discovery of Pluto.
- http://perso.orange.fr/olivier.granier/meca/vulga/pluton/pluton.htm

The Planet Mars: A History of Observation and Discovery
- On-line version of the book by William Sheehan.
- http://www.uapress.arizona.edu/onlinebks/mars/contents.htm

Is Mars Habitable?
- A. R. Wallace's 1907 critique of Lowell's Book "Mars and Its Canals"
- http://www.wku.edu/~smithch/wallace/S730.htm

Neptune's Discovery
- Article in Astronomy Magazine.
- http://www.astronomy.com/Content/Dynamic/Articles/000/000/000/119ipise.asp

Exploring The Planets-Discovery
- The five known in antiquity, three more since the telescope, and Ceres.
- http://www.nasm.si.edu/ceps/etp/discovery/etpdiscovery.html

Exploring the Moon
- Timeline of Lunar exploration.
- http://www.space.edu/moon/

Orbits and Gravitation
- The development of the mathematics of planetary motion.
- http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/Orbits.html

Neptune and Pluto
- Mathematical discovery of planets
- http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/Neptune_and_Pluto.html

Asteroid Discovery Circumstances
- For each minor planet: Where and when found, and by whom.
- http://ssd.jpl.nasa.gov/dc_home.html