Discovering the Outer Planets
Until 1781 Saturn was thought to be the outer edge of the solar system
The known planets M, V, M, J, S are all:
easy to see
On one clear bright night in March (13th) this all changed
William Herschel (1738 - 1822) a German immigrant and professional musician / amateur
astronomer thought he had found a comet.
He was systematically measuring the brightness and positions of
stars that he could view w/ a
small (?) telescope (serendipity?)
IT IS VISIBLE WITHOUT A TELESCOPE!
He reported it to other astronomers as a comet, but no tail appeared and the brightness
So he named it Georgium Sidus - George's Star
Why? He didn't want "On the Road Again" to remain his theme song
Other Major Works
Built big telescopes
Double (binary) stars - 1803
Clockwork Universe w/ son
Other Happenings in 1781?
Yanks beat Brits in 11th at Yorktown. French relieve Kosciusko for the save
Kant publishes Critique of Pure Reason
Sister Caroline his older sibling (13 yrs) - A victim of a "women's place"?
Son John - Cape of Good Hope (1834 - 1848) -star catalogs
1st person to use the word photography (1839) in print - considered a brilliant
So now all the astronomers are asking . . .?
In 1821 Uranus is not where it is supposed to be
Old star charts from 1600s are discovered with Uranus on them and the positions
long revolution - 84 yrs. so you now have data from 1.5 revolutions
Mathematicians have had the Principia
for over a 100 yrs so you know what they've been doing - refining celestial
Yes, perturbation is rearing its ugly head.
1843 - John Couch Adams a student at Cambridge comes up with a solution that puts
an unknown planet in Aquarius
He writes John Airy, the Royal Astronomer of Great Britain
and guess what?
1846 - Urbain Leverrier publishes his independent solution and guess what?
Now Airy hops to it and tells the Cambridge Observatory to search the sky at this
and guess what?
September 23, 1846 - Johann Galle (and his proverbial student) at the Berlin Observatory
are the first to observe Neptune and know it is a planet
A triumph of MATHEMATICS? I think not
Assumptions that both Adams & Leverrier made
Orbit is 2x > than Uranus (Uranus 2x> Saturn)
This means 38AU and has orbital period of 217 yrs
Eccentricity of .1 (which is large) and
at perihelion in 1820
almost circular orbit ( .010 - only Venus smaller)
So the only time the model fit the reality was in 1846 +
and maybe it would not have been found
Remember Percival Lowell and his telescope in Tucson?
He is now searching for a new planet!
He predicts that it will be 6x> earth mass at 43 AU and it can be found in the Gemini
Problem - the Gemini star field is heavy populated. He searches from 1905 until
his death in 1916.
His last wish of a wide-angle telescope is fulfilled by his brother in 1927 at a
cost of $10,000.
1929 Clyde Tombaugh uses the new scope with a camera
2 plates a week apart
number of stars / plate >100,000
February 18, 1930 - he finds the new planet just 6o from Lowell's predicted position
Another victory for mathematics?
Luck favors the prepared mind?