Transcript Neptune discovery in physics class: activities and simulations

Discovery of Neptune:
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: Orbits of Planets
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 mass attracts every other mass by
a force pointing along the line intersecting both
masses. 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 AU.
• 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 at
distances as far away as Uranus; i.e., the law of
gravitation is not universal !!!
OR
2. The law of gravitation is correct but there is
another unseen planet far beyond Uranus
whose gravity pulls on Uranus.
Where to look for the new planet?
Bode-Titus law (1772)
• A rule for the distances of planets from the
n
r

0.4

0.3

2
Sun
n
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 known scientist,
whereas Adams was a young Cambridge
undergraduate, 26 years old, who seems
to have taken on a 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 (just two months after
Adams), 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?
Adams wrote to George Airy, providing 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, Airy had a strong negative reaction to
Adams paper. The problem was that Airy was
strongly opposed to theoretical investigations and
skeptical of the abilities of younger scientists.
Star Map from the Day of Discovery
Who was Neptune’s discover
Le Verrier, Adams or Galle?
Classroom Activities
• Finding the year when Uranus lines up with
Neptune.
MATLAB Numerical Simulations
of Planet Orbits Using
Feynman’s Method
The program can calculate different
Neptune
physical quantities.
Uranus
Simplifying Assumptions
• Assuming circular orbits, conservation of
energy and angular momentum, the students
will find the distance to Uranus when it lines
up with Neptune.
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