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

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

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

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

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

Notes on Sunspot Observations
John Winthrop's 1739 notes, from the collected papers of Fredrick Kilgour.
http://www.oclc.org/pdemo/kg/p012.htm

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

Is Mars Habitable?
"
http://www.wku.edu/~smithch/wallace/S730.htm

The Face of the Moon
A catalog for an exhibition of rare books and maps. Includes sample pictures from Galileo to the Apollo missions.
http://www.lindahall.org/events_exhib/exhibit/ex_face_moon.shtml

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