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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 the observed and the calculated longitudes of Uranus
after known causes have subtracted
Dis
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anci
es b
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calc
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long
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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 Sun 0.4 0.3 2nnr
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 physical quantities . Neptune
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
