1. Earth Among the Stars Earth Rotates… Earth rotation causes…
15o per hour
From west to east
On its axis tilted 23.5o
Earth rotation causes…
Apparent motion of Sun
Apparent motion of the Moon across sky
Apparent motion of the stars
REMEMBER…they’re not moving, WE ARE!

2. Earth’s Rotation Axis points to Polaris Polaris is the “Pole Star”
Stars close to the pole appear
to move around Polaris
These stars are CIRCUMPOLAR

3. CIRCUMPOLAR STARS

4. CIRCUMPOLAR STARS appear to rotate around Polaris
They never set!

5. Star Apparent Motion Circumpolar constellations go around Polaris
All other stars appear to rise in the East, move across the sky and set in the West

6. More Evidence of Earth’s Rotation
Foucault’s pendulum will appear to change its direction of swing…
If Earth did not rotate it would continue to swing in its normal direction!

7. Even MORE Evidence for Rotation
Coriolis Effect…
Objects moving over the earth are deflected (curve away) from their direction of motion
This is caused by Earth’s Rotation!
Northern Hemisphere – right curve
Southern Hemisphere – left curve

11. Evidence for Earth’s Revolution
Earth revolves 360o in 365 days… about 1o per day!
Causes the change in seasons!
Stars change positions in different seasons!
We see different constellations through the year!

12. Constellations Change Places!

13. What does revolution cause?
In June, we see Scorpio at night
In August, we
See Capricorn

14. Earth’s Orbital Path Earth’s orbit LOOKS circular…but its an ellipse!
The orbits of ALL PLANETS are ELLIPTICAL
Perihelion
Aphelion

15. EARTH’s orbit is SLIGHTLY ECCENTRIC!
EARTH is farther
to the sun
EARTH is closer
to the sun
152 million km
147 million km
When is perihelion?
When is aphelion?
Jan. 4th…WINTER!
July 1st …SUMMER!

16. Appearance of Sun Changes with Varying Distance
BIGGER in
WINTER
smaller in
summer

17. SPEED of EARTH in its ORBIT
EARTH travels faster at PERIHELION…
And slower at aphelion
Perihelion
Aphelion
The gravitational attraction to the sun is greater!

18. ELLIPSE SHAPES Eccentricity: How “out of round” an ellipse is!

19. ELLIPSE ECCENTRICITY Eccentricity = Distance between foci
Length of Major Axis
2.0
Eccentricity =
2.0
4.0
4.0
Eccentricity = 2.0 / 4.0 =

20. ELLIPSE ECCENTRICITY Eccentricity = Distance between foci
Length of Major Axis
Calculate the eccentricity of an ellipse…
Distance between the foci= 2.3cm
Length of the major axis is 9.2cm

21. Planet Eccentricity Check out the ESRT… Planetary Data
Which planet has the greatest eccentricity?
What does this mean?
Which planet has the lowest eccentricity?
Does there seem to be a relationship between eccentricity and a planet’s distance to the sun? Explain…