1. Earth in Space
Section 19.1

2. Earth’s Shape Considered to be ellipsoid Oblate spheroid
Earth is wider
than it is tall
Bulges at equator,
flattened at poles

3. Earth’s motions
Rotation – spinning on an axis
- causes day and night

4. Earth’s Motions 1. sidereal day The time it takes the Earth to
rotate once with respect to a
reference star.
One 360° Rotation
Time = 23 hr. 56 min.
1-2: Globe rotates 360° - sidereal
1-3: Globe re-points to sun - synodic

5. Earth’s motions 2. solar (synodic) day = 24 hours
The time it takes Earth to rotate once with respect to the sun.
(Sun’s Highest point in sky to the
next highest point in sky).

6. Earth’s Motions
Revolution – movement around a fixed point (sun)

7. Earth’s Motions - Revolves once every 365.25 days (year)
need leap years
- elliptical shaped orbit
- Jan million km from sun (perihelion)
- July million km from sun (aphelion)

8. Seasons on Earth Earth’s axis is tilted 23.5o
The area tilted towards sun has longer days and more radiant energy (summer)
The area tilted away from
the sun has shorter days
and less radiant energy (winter)

9. Vernal equinox
March 20 or 21
Solstice – the sun reaches the greatest distance north or south of the equator
Summer solstice
June 21 or 22
Longest day
Winter solstice
Dec 21 or 22
Shortest day
Equinox- the sun
is directly above
the equator.
Equal daylight and night time hours all over the world
Autumnal equinox
Sept 22 or 23

10. Earth’s Motions
Precession – Earth’s wobble

11. Earth’s Orbit
Law of universal gravitation: every object in the universe attracts every other object.
Isaac Newton

12. Attracts all objects towards each other.

13. Depends on two factors:
MASS
DISTANCE
The amount of
matter (stuff)
in an object
STRONGER

14. MASS WEIGHT The amount of matter (stuff) in an object Does not changeVS
The amount of matter (stuff) in an object
Does not change
Force ( a push or pull) of gravity on an object.
Changes depending on where you are.

15. 265 lbs
=120 x 1.6
About 45 lbs

16. Earth’s Orbit
Inertia – the tendency of an object to resist change in motion
Newton’s first law of motion
An object in motion will stay in motion, in straight line, at a constant speed unless acted upon by an outside force

17. Earth’s Orbit Newton concluded that 2 forces (inertia, gravity)
Inertial force
Newton concluded that
2 forces
(inertia, gravity)
combine to keep
Earth in orbit
around the sun
Gravitational
force
Earth’s motion around the sun,
Not as easy as I thought