1. 22.1 Early Astronomy

2. Solar System Models Geocentric model: Geo= Earth Center=Middle
Previous model of the universe that states: Earth is the center of the universe (NOT TRUE!)
believed until 1600’s

4. Helio= Sun Center= Middle
Heliocentric model:
Helio= Sun Center= Middle
Current model of the solar system that states that the sun is the center of the solar system and the planets revolve around it

6. The stars don’t seem to move in our sky; BUT planets do because:
they are much closer than stars!

7. The planets move in an eastward movement
Sometimes planets appear to move in a backward movement amongst the stars, this is called retrograde motion (westward)
This loop occurs because each planet travels around the sun at different speeds

8. Watch retrograde motion!

9. The path a planet follows around the sun is called its orbit
Is the sun at the center?

10. Elliptical Orbits
The Sun isn't at the center of a planet's elliptical orbit! An ellipse has a point a little bit away from the center called the "focus". The Sun is at the focus of the ellipse- not the center

11. Kepler’s Laws of Planetary Motion
1st law : planets orbit the sun in a path called an ellipse
2 focal points = foci

12. Planets move closer to and further away from the Sun every orbit.
Perihelion
Peri= near
Sun
Planets move closer to and further away from the Sun every orbit.
Aphelion
Ap= away

13. AU-astronomical unit: the average distance between Earth and the sun
150 million km
which is: 150 BILLION meters

15. 2nd law: Planets don’t travel a the same speed
2nd law: Planets don’t travel a the same speed. They move fastest when they are closest to the sun.
Why?: Gravity of the sun!

16. 3rd law: The period of revolution of a planet is related to the planet’s distance to the sun
(The farther away a planet orbits, the longer the planet takes to revolve around the sun.

18. Protons, Neutrons, and Electrons
What makes an atom?
Protons, Neutrons, and Electrons
TRILOGY