Transcript Neptune discovery in physics class: activities and simulations

Neptune discovery in physics
class: activities and simulations
Hezi Yizhaq, Environmental High School, DAT Fulbright
Teacher from Israel
Email Address: [email protected]
Matthew Bobrowsky, Department of Physics, University of
Maryland
Email Address: [email protected]
Introduction: Planet Orbits
Kepler's laws of planetary motion are three scientific
laws describing orbital motion, each giving a description of
the motion of planets around the Sun (1619).
Kepler's laws are:
1. The orbit of every planet is an ellipse with the Sun at one of the
two foci.
2. A line joining a planet and the Sun sweeps out equal areas during
equal intervals of time.
3. The square of the orbital period of a planet is
directly proportional to the cube of the semi-major axis of its orbit.
Newton's law of universal gravitation
(1687) explains Kepler’s laws
Every point mass attracts every single other
point mass by a force pointing along
the line intersecting both points. The force
is proportional to the product of the
two masses and inversely proportional to
the square of the distance between them
Uranus –A very badly behaved planet
• Discovered by William Herschel in 1781
• Period of revolution 84 years, average
distance from the Sun is: 19.22AU.
• After 1800 discrepancies started to be
apparent between the planet position as
predicted by theory and as measured in the sky
Discrepancies between calculated
to observed longitudes
Discrepancies between the observed
and the calculated longitudes of Uranus
after known causes have subtracted
An Astronomical Mystery
Two possible explanations:
1. Newton's law of gravity might not hold as
distances as great as Uranus i.e. the law of
gravitation is not universal !!!
2. The law of gravitation is correct but there is
another unseen planet far beyond Uranus
which perturbed its orbit.
Where to look for the new planet?
Bode Titus law (1772)
• An empirical law for the distances of planets
from the Sun rn  0.4  0.3 2n
The Search for the Missing Planet
Independently, two astronomers, John
Couch Adams in England and Urbain Jean
Josef Le Verrier in France, calculated the
position of this yet unknown planet.
Le Verrier was already a know scientist
whereas Adams was a young Cambridge
undergraduate, 26 years old, who seems
to have taken on a own personal quest to
search for an explanation for the apparent
misbehavior of Uranus.
Urbain Le Verrier
John Couch Adams
Neptune Discovery Chronology
• In October 1845, Adams wrote to George Airy,
the Astronomer Royal of Greenwich
Observatory, claiming that he had solved the
problem of Uranus' orbit, and stating the
position where the unknown planet could be
found.
• In December 1845 Le Verrier independently
published a short manuscript on the orbit of
the missing planet.
• Neptune was ultimately discovered by the
German astronomer Johann Galle, on
September 29, 1846, using Le Verrier’s
predictions.
Why Neptune was not discovered in
England?
In October 1845, Adams wrote to George Airy, the Astronomer Royal of
Greenwich Observatory, claiming that he had solved the problem of Uranus' orbit,
and stating the position where the unknown planet could be found. Now, if Airy
had pointed a telescope at that spot, he might have found Neptune (however, not
at the exact spot that Adams had pinpointed).
Although, he tried to conceal it, Airy had a strong negative reaction to Adams
paper. His altitude later turned out to be of critical importance to the fact that
Neptune was not discovered in England. The problem was that Airy was strongly
opposed to theoretical investigations and skeptical of the abilities of younger
scientists. He was not the sort of man to take a leap into the scientific unknown.
“God forgive me for writing in this way – The truth lies on the other
side & Adams is the 1st theoretical discoverer of Neptune. The
whole thing was parried [?] and perverted by Airy’s indefensible
reticence. On him be the responsibility of the (temporary) transfer
of one of the brightest stars in Britain’s Scientific fame to
France. “ British Astronomer John Herschel-1846
Star Map from the Day of Discovery
Who was Neptune’s discover Le
Verrier, Adams or Galle?
Developed Activities
• Finding the year of conjunction by performing
time numerical derivative of the data
MATLAB Numerical Simulations
of Planet Orbits Using
Feynman’s Method
The program can calculate different
Neptune
physical quantities
Uranus
Calculation of the perturbation near
the conjunction
• Assuming: Circular orbits, conservation of
energy and angular momentum of the system
the students will find the perturbed radius of
the planet near the conjunction
Numerical Solution of the Corrected Orbit of Uranus
(unperturbed orbit=19.22AU,R2=38.8AU )
The Discovery of Neptune and the
Dark Matter in the Universe
Rotation Curves in the Solar System
Rotation Curves in the Milky Way
Thank you for attention