Phys 214 Planets and Life Dr Cristina Buzea

Phys 214. Planets and Life Dr. Cristina Buzea Department of Physics Room 259 E-mail: cristi@physics. queensu. ca (Please use PHYS 214 in e-mail subject) Movie + Lecture 3. Exercise on Kepler’s laws (Page 28 -30) January 11

Lecture 3 Textbook: Pages 28 and 30 • Movie on Kepler’s laws • Kepler`s third law calculations

Movie on Kepler’s laws “We are star stuff!” Cosmos series (Emmy award winning series) By Carl Sagan Part III: The harmony of the world. Episode 8 (35 min)

Kepler’s Third Law Kepler’s third law: More distant planets orbit the Sun at slower average speeds, obeying the precise mathematical relationship. p 2=a 3 where p is the planet’s orbital period in years, and a is the average distance (semimajor axis) from the Sun in astronomical units (AU). 1 AU = Earth’s average distance from the Sun about 149. 6 million km • • • Kepler’s law applies to any orbiting object as long as the following two conditions are met: The object orbits the Sun or another star of exactly the same mass. We use units of years for the orbital period and AU for the orbital distances.

Kepler’s Third Law Kepler’s third law: p 2=a 3 where p is the planet’s orbital period in years, and a is the average distance (semimajor axis) from the Sun in astronomical units (AU).

Kepler’s Third Law Exercise 1. (similar to exam question): The largest asteroid, Ceres, orbits the Sun at an average distance (semimajor axis) of a = 2. 77 AU. What is Ceres orbital period p? Answer: Ceres has an orbital period of 4. 6 years Exercise 2. (similar to exam question): • A planet is discovered orbiting every three month around a star of the same mass as the Sun. What is the planet average distance a? Answer: The planet orbits star at an average distance of 0. 4 AU. 20

Next Lecture Modern science and essential concepts of physics & astronomy Textbook: Pages 33 -43, 81 -88 MOVIE. Hubble - 15 years of discovery (15 minutes) Chapter 5. Monsters in space, black holes, worm holes, gamma rays. Chapter 6. Gravitational lensing