Transcript LeVerrier (French)

NEPTUNE
• initial attempts to produce orbit for Uranus unsuccessful
• 1821: Bouvard produces orbit based on contemporary
observations
• includes gravitational influences of Jupiter and Saturn
• deviations between
prediction and observations
(perturbations) increase with
time
• discrepancy possibly due to
gravitational perturbations of an
unknown planet
Problem: use the observed perturbations to predict location of
the unknown
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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)
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
• Leverrier's ephemeris sent to Galle at Berlin Observatory
(Sept. 23, 1846)
• 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
• must be planet - Neptune
The Aftermath
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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
Mercury
• 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
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
Pluto and Charon
• orbit: 39.5 AU, period 248 years
• perturbations of Uranus were not produced by Pluto
MOONS AND MINOR BODIES
• many new moons discovered as telescope resolution improves
Deimos
• 1877 - 2 moons of Mars
Phobos
• 1978 - Pluto's moon Charon
• 2005 - 2 more moons for Pluto
(discovered with HST)
• Jupiter - 63, Saturn - 34
Oort Cloud (1950)
• 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
• Eris (2006) - larger than Pluto
Quaoar’s orbit
Sedna
Dwarf Planets (August 2006)
• round due to gravity
• not heavy enough to clean majority of nearby space
• Pluto, Ceres
Trans-Neptunian Objects