1. What is the universe Part 2 Motion in Space

2. The Heliocentric Model
From 5,000 ago until the 1500s, a geocentric view of planetary motion was widely accepted
Polish astronomer Nicolas Copernicus developed the first heliocentric model in which the planets orbit the sun in circles

3. Problems with the Geocentric Model
Assumed that planets and stars orbited a stationary Earth
Could not explain the apparent retrograde motion of some planets (Mars)
Retrograde motion= planets further from the sun move slower in their orbit due to less gravitational pull and appear to move backwards

4. From Circles to Ellipses
Danish astronomer Tycho Brahe studied the movement of Mars taking nightly measurements WITHOUT a telescope
Accurately measured the elliptical orbit within a matter of degrees
Died in 1602, seven years
before the telescope was
invented

5. Brahe’s Apprentice
Johannes Kepler (Brahe’s apprentice) was in the right place at the right time and used Brahe’s data to proposed the first of a set of three laws that are named after him

6. Kepler’s Laws The planets move around the sun in ellipses
The imaginary lines connecting the sun to each planet sweeps equal areas in equal time
The relationship between a planet’s ellipse and its orbital period is: P2 = a3 (where P equals the orbital period and a equals the length of the semi-major axis)

7. Eccentricity
Due to its elliptical orbit, a planet is not at a constant distance from the Sun
Perihelion = closest to
Aphelion = farthest from

8. Kepler’s Second Law

9. Kepler’s Third Law
The farther a satellite is from the object it is revolving aroung:
1. The longer it will take to complete an orbit
2. The greater the distance it will travel to complete the orbit
3. The slower its average speed of motion

10. Newton’s Laws (physical science review!)
An object in motion tends to stay in motion UNLESS an outside forces acts upon it
An object accelerates in the same direction of the force applied
For every action, there is a equal and opposite reaction

11. Kepler + Newton Gravity pushes planets towards the sun
The gravitational force holding the planets on their orbit is continuously changing the planets’ velocity creating elliptical orbits
When planets are closer to the sun, they speed up!

12. Why does the night sky change?
Parallax
Precession
An apparent change in the direction of an object, caused by a change in observational position that provides a new line of sight.
Earth’s wobble on its tilted axis
It takes the Earth about 26,000 years to wobble
It is caused by a tug of war on Earth by the Sun and Moon, but the Moon’s pull is stronger due to proximity

13. Our Motion & the Moon
Nutation
Barycenter