1. Earth in Space

2. How Earth Moves
Earth moves through space in two major ways: rotation and revolution
Rotation – The spinning of Earth on its axis
Axis – an imaginary line that runs through Earth’s center and the North and South Poles
Makes one complete rotation on its axis every 24 hours – we call this a day

3. Revolution Revolution – the movement of one object around another
Earth travels around the sun
One complete revolution around the Sun is called a year (~ 365 Days)

4. Earth’s Orbit Around the Sun
Earth follows a path, or orbit as it revolves around the sun
It follows an elliptical path – (slightly elongated circle – an ellipse)

5. Earth’s Seasons
Most places (besides the tropics and polar regions) have four distinct seasons – but have great differences in temperature
This is due to how sunlight hits the Earth
Direct sunlight (steep angle at equator)
Indirect sunlight (spread out at poles)

6. Earth’s Tilt and the Seasons
Earth has seasons because its axis is tilted as it revolves around the sun
Always tilted at 23.5 degrees
As Earth revolves around the Sun – the North end of its axis is pointed towards the Sun part of the year and away from the Sun part of the year

7. The Seasons
Summer and Winter are caused by Earth’s tilt as it revolves around the Sun
It is not caused by changes in the Earth’s distance from the Sun
( Earth is actually further from the Sun in the Summer in the Northern Hemisphere)

8. Solstices and Equinoxes
Solstice – When the sun is the greatest distance North or South of the Equator
occurs twice a year
When sun is farthest North of the Equator it is our summer solstice ( June 21 )
When sun is farthest South of the Equator it is our winter solstice ( Dec 21 )

9. Equinoxes Equinox – means “equal night “
Day and night are approximately 12 hours long
Occurs halfway between the solstices
March 21 and September 22
The noon sun would be directly overhead at the equator

10. The Role of Gravity Gravity is a force
Force = a push or a pull
The Law of Universal Gravitation – every object in the universe attracts every other object

11. Universal Gravitation
The strength of the force of gravity between objects depends on two things
The mass of the objects
The more mass the more gravity
The distance between the objects
The closer the objects are the more gravity between the objects

12. Inertia and Orbital Motion
If the sun and Earth are constantly pulling on one another – why doesn’t the Earth fall into the sun?
Because of inertia
Inertia – the tendency of an object to resist a change in motion
Newton’s 1st Law of Motion – objects in motion stay in motion, objects at rest stay at rest unless acted upon by an outside force

13. Orbital Motion
Inertia and gravity combine to keep the Earth in orbit around the sun – and the moon in orbit around the Earth