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° - sidereal1-3: 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 (perihelion)

- July 4 - 152 million km from sun (aphelion)

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)

Winter solsticeDec 21 or 22Shortest day

Summer solsticeJune 21 or 22Longest day

Vernal equinoxMarch 20 or 21

Autumnal equinoxSept 22 or 23

Solstice – the sun reaches the greatest distance north or south of the equator

Equinox- the sunis directly abovethe equator.Equal daylight and night time hours all over the world

Earth’s Motions

• Precession – Earth’s wobble

• Law of universal gravitation: every object in the universe attracts every other object.

Earth’s Orbit

Isaac Newton

• Attracts all objects towards each other.

• Depends on two factors:

MASS DISTANCE

The amount of matter (stuff) in an object

STRONGER

MASS

• The amount of The amount of matter (stuff) matter (stuff) in an objectin an object

• Does not Does not changechange

WEIGHT

• Force ( a push Force ( a push or pull) of or pull) of gravity on an gravity on an object.object.

• Changes Changes depending on depending on where you are.where you are.

VS

265 lbs

About 45 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

Gravitationalforce

Newton concluded that

2 forces (inertia, gravity) combine to keep

Earth in orbit around the sun

Earth’s motion around the sun,Not as easy as I thought