Earth in Space - PowerPoint by 62I0JCj

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```									Earth in Space

Section 19.1
Earth’s Shape

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

• Rotation – spinning on an axis
- causes day and night
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
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).
Earth’s Motions

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

- Revolves once every 365.25 days (year)
need leap years
- elliptical shaped orbit
- Jan. 3 - 147 million km from sun
- July 4 - 152 million km from sun
Seasons on Earth

o
• Earth’s axis is tilted 23.5
• The area tilted towards sun has longer
days and more radiant energy (summer)
• The area tilted away from
the sun has shorter days
Vernal equinox    Solstice – the sun
March 20 or 21    reaches the greatest
distance north or
south of the equator

Summer solstice
June 21 or 22                             Winter solstice
Longest day                               Dec 21 or 22
Shortest day

Equinox- the sun
is directly above
the equator.
Equal daylight
and night time
Autumnal equinox
hours all over the
Sept 22 or 23
world
Earth’s Motions
• Precession –
Earth’s wobble
Earth’s Orbit

• Law of
universal
gravitation:
every object in
the universe
attracts every
other object.     Isaac Newton
• Attracts all objects towards each other.
• Depends on two factors:

MASS                      DISTANCE
The amount of
matter (stuff)
in an object
STRONGER
MASS           VS      WEIGHT
• The amount of         • Force ( a push
matter (stuff)          or pull) of
in an object            gravity on an
object.

• Does not              • Changes
change                  depending on
where you are.
265 lbs

=120 x 1.6
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
Earth’s Orbit
Inertial force
Newton
concluded that       Gravitational
2 forces         force

(inertia, gravity)
combine to keep
Earth in orbit
around the sun

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