1. initial attempts to produce orbit for Uranus unsuccessful 1821: Bouvard produces orbit based on contemporary observations includes gravitational influences of Jupiter and Saturn discrepancy possibly due to gravitational perturbations of an unknown planet deviations between prediction and observations (perturbations) increase with time Problem: use the observed perturbations to predict location of the unknown NEPTUNE

2. Adams (English) approximate method to determine location and mass (1843) used Newton's laws of Mechanics and Gravitation assumed circular orbit, twice the radius of Uranus' dropped assumptions when more accurate data obtained calculated orbit and mass of the unknown (1845) orbit presented to Challis and Airy at Cambridge Observatory search delayed due to concerns of Challis and Airy LeVerrier (French) determined size of perturbations very precisely by examining effects of Jupiter and Saturn assumed orbit fit T-B law (38.8 AU) also used Newton's Laws produced ephemeris (August, 1846)

3. The Race Adams becomes aware of Leverrier's work, requests Challis begin search for object Challis begins observing (July 1846) Cambridge lacked detailed sky maps of region necessitates large amount of data analysis, Challis reluctant uses new Star Map of the Berlin Academy (created in response to discovery of asteroids) locates a new object within 52' of prediction Galle and Enke confirm object moves Leverrier's ephemeris sent to Galle at Berlin Observatory (Sept. 23, 1846) must be planet - Neptune

4. The Aftermath British had observed Neptune on Aug. 4 and 12 didn't analyse the observations until after discovery at Berlin controversy over credit Galileo may have observed it in 1612-13 Neptune's orbit has radius of 30.1 AU, period 164 years T-B law discredited discovery added credence to Newton's theories LeVerrier examines Mercury's orbit perihelion advance (1.5° per century) gravitational perturbations account for all but 40" of the advance suggested existence of another planet (Vulcan)- never found Mercury

5. PLUTO Uranus' orbit apparently still had unaccounted perturbations Lowell predicts position of another unknown object Clyde Tombaugh searches for planet at Lowell Observatory uses blink comparator Feb. 1930: discovers object within 6° of Lowell's prediction – Pluto perturbations of Uranus were not produced by Pluto Pluto and Charon orbit: 39.5 AU, period 248 years

6. MOONS AND MINOR BODIES many new moons discovered as telescope resolution improves 1877 - 2 moons of Mars Jupiter - 63, Saturn - 34 1978 - Pluto's moon Charon 2005 - 2 more moons for Pluto (discovered with HST) Phobos Deimos

7. collection of rocky/icy bodies out to 50,000 AU home of long-period comets Kuiper Belt (1951) rocky objects beyond Pluto, out to 500 AU home of short-period comets Quaoar, Sedna - similar to Pluto Sedna Quaoar’s orbit Eris (2006) - larger than Pluto Oort Cloud (1950)

8. round due to gravity not heavy enough to clean majority of nearby space Pluto, Ceres Trans-Neptunian Objects Dwarf Planets (August 2006)