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Message started by frankuitaalst on 08/17/07 at 14:41:21

Title: Neptunes discovery
Post by frankuitaalst on 08/17/07 at 14:41:21

Some history : (extract from the Wikipedia , Neptune Discovery )
"In 1821, Alexis Bouvard published astronomical tables of the orbit of Uranus.[13] Subsequent observations revealed substantial deviations from the tables, leading Bouvard to hypothesize some perturbing body. In 1843, John Couch Adams calculated the orbit of an eighth planet that would account for Uranus' motion. .....
Urbain Le Verrier, independently of Adams, produced his own calculations ......
Though still a student at the Berlin Observatory, Heinrich d'Arrest suggested that a recently drawn chart of the sky, in the region of Le Verrier's predicted location, could be compared with the current sky to seek the displacement characteristic of a planet, as opposed to a fixed star. Neptune was discovered that very night, September 23, 1846 within 1 of where Le Verrier had predicted it to be "

It is really astonishing that people in that time were able to predict the location of an undiscovered body !
In order to get some understanding about the influence of Neptune and Pluto upon the orbit of Uranus I ran two simulations with GravSim ...

The first started in 2007 with all known planets , going back in time...
The second was run from 2007 on but without Neptune and Pluto .
Going back in time for about 200 years this yields 2 positions for Neptune : the position it had then and the position it should have had if Neptune and Pluto didn't exist .
So , if 186 years ago (1821) Levivier had the Tables of the orbit this tables should predict the Uranus position without Neptune and Pluto .
In 1846 (164 years ago) he discovered serious displacements from the predicted position and also calculated the predicted position of the disturbing body ...
The plot hereunder gives the differences between the position of Uranus in degrees (X/distance) and (Z/distance) in both cases .( call it "longitude" and "azimuth" ) .
The differences over a timespan of 22 years of observation are about only 0.06 degrees ( equivalent to an angle of 10mm/10 meter) .
It is really amazing that more than 150 years ago people were able to calculate the position of an unknown body with unknown mass out of these differences :-[

Title: Re: Neptunes discovery
Post by frankuitaalst on 08/18/07 at 04:00:11

A correction to the graph above :
The axis of anglez was not visible due to the black background .
Here is the evolution of the difference in position from 2007 on , back in time .
The influence of Neptune / Pluto is max 0.09 degrees in the longitude .
One may say this approach is not fully correct . He is right .
To be correct the simulation has to be done backwards till the year 1821 (time of the "table") and then run again forwards two times ; once with Neptune and once without Neptune till the year of the discovery .
I think the deviations may even be smaller , giving an even bigger value to the work done !

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