1. Effects of Planetary Motion

2. What do you see in the sky?
Sun & Moon
Both rise in the east and set in the west
Stars, constellations and asterisms
Most rise in the east and set in the west
Why do they appear to rise in the east and set in the west?
Moon
Each night rises 1 hour later than previous night
Changes phases
Full moon rises exactly at sunset
Never see the backside of the moon
Sun
Rises earlier and farther north each morning from end of December to end of June
Through summer and fall rises later and sets earlier a little farther south each day

3. THE EARTH ROTATES!

4. Rotation Rotation is the spinning of an object around its axis.
The Earth’s axis:
Imaginary line joining North and South pole
If continued northward into space it would pass through Polaris (North Star)
Earth takes 24 h or 1 day to rotate once
Model rotation on the spot

5. Revolution The movement of one object travelling around another
How does this relate to the Earth?
Earth takes 365 days or 1 year to revolve once around the sun
What does this affect?
Causes the seasons
Model revolution around desk
Desk = sun
Revolution combined with earth’s tilt cause seasons

6. Retrograde Motion
Planets that appear to change their path in the sky relative to the background stars.
Instead of traveling West to East, they appear as though they are travelling East to West.
Only the planets beyond Earth will experience this Retrograde Motion

7. Do both planets & stars move in the sky?
NO!
Stars
Don’t move, they only appear to move because the Earth is moving
Planets
Appear to “wander” through the constellations because they are also revolving around the sun (retrograde motion)
Planets
Wander eastward (opposite westward motion of stars) against their starry background
Greek for wanderer
They called these objects planets, meaning wanderers, and named them after Roman deities - Jupiter, king of the gods; Mars, the god of war; Mercury, messenger of the gods; Venus, the god of love and beauty, and Saturn, father of Jupiter and god of agriculture.

8. Homework
Would it be a good idea to use stars to indicate direction when travelling?
Explain why a constellation:
Appears to change position during the night (i.e. from hour to hour)
Is at a different location at the same time on different nights No
Stars cannot be seen in the day
Earth rotates during the day and revolves over the year so stars appear to move in the sky
Polaris one good star to use as it is in line with earth’s axis and does not move….can only use it if u r North of the equator
Only constellations we see all year are those near polaris
Due to rotation on axis
Due to revolution around sun