1. Kepler’s Laws EARTH SCIENCE

2. Early Astronomy The Birth of Modern Astronomy  Johannes Kepler
• Kepler discovered three laws of planetary motion:
1. Orbits of the planets are elliptical.
2. Planets revolve around the sun at varying speed.
3. There is a proportional relationship between a planet’s orbital period and its distance to the sun.

3. 22.1 Early Astronomy The Birth of Modern Astronomy  Johannes Kepler
• An ellipse is an oval-shaped path.
• An astronomical unit (AU) is the average distance between Earth and the sun; it is about 150 million kilometers.

4. Planet Revolution
Makes no sense without caption in book

5. The Solar System Model Evolves
Makes no sense without caption in book

6. Gravity’s Influence on Orbits
Makes no sense without caption in book

7. Note:
The seasons are NOT caused by the distance from the sun.

8. Let’s see some ellipses

10. Not drawn to scale! The shape is more like a circle
Perihelion Jan 3 93,000,000 miles
Aphelion July 4 95,000,000 miles
Not drawn to scale! The shape is more like a circle

11. Kepler’s Laws
1) All planets travel in elliptical orbits with the sun at one focus.
Note: The Earth's orbit is so close to a perfect circle that it can't be distinguished with the human eye.

12. An ellipse: the sun as one foci

13. 2) Each planet travels in such a way that a line joining the planet and the sun sweeps equal areas in equal times.

14. March
April
February
May
June
January
July
August
September
December
October
November

15. 3) Relationship between distance and period: P2 = D3
Where P is the Period in Earth Years
And D is the distance in “AU’s”
An “AU” is an astronomical unit, which is the average distance from the sun to the Earth.

16. Kepler’s Third Law
In this equation P represents the period of revolution for a planet and R represents the length of its semi-major axis.
Kepler's Third Law implies that the period for a planet to orbit the Sun increases rapidly with the radius of its orbit.
Thus, we find that Mercury, the innermost planet, takes only 88 days to orbit the Sun but the outermost object (Pluto) requires 248 years to do the same.