Earth’s Stucture and Motion

Origin of the Solar System

• Nebular hypothesis – 4.6 billion years ago a great cloud of gas and dust collapsed from its own gravity and spun into the center which compressed the material so much that hydrogen fusion occurred creating the sun.

• Planets formed from remaining material from around the sun by collecting loose materials through the pull of gravity

Earth is Spherical

• Travel long distances north-south and watch the stars. Suppose you see a star low on the southern horizon, and then walk or sail many hundred miles south. The star will now appear to be higher in the sky, well above the horizon, as Aristotle knew from the accounts of sailors. If the Earth were flat, this would not happen; a star which was low on the horizon would remain so as you traveled.

Earth is Spherical

Earth is Spherical

• Watch a boat sail away from shore. Of course, it gets smaller in appearance by virtue of its increasing distance, but it also seems to disappear over the horizon as though it is going down the far side of a hill. The hull disappears first, and soon only the tops of the masts and flags are visible.

Earth is Spherical

Earth is Spherical

• Watch eclipses: One can notice, as did Aristotle, that whenever there is a lunar eclipse, the edge of the Earth's shadow (which we see projected onto the lunar surface) always looks like the arc of a perfect circle.

Earth’s Shape and Size

• Oblate Spheroid: The Earth's True ShapeThe Earth is not a perfect sphere. Due to it's rotation, the Earth (like all rotating planets) has a slightly distorted shape. The rotational momentum tends to force the matter to bunch up in the middle. In the case of the Earth, this "middle" is the equator.

• One of the most important things to remember about the Earth's shape is that it is only very slightly oblate. The diameter from the North Pole to the South Pole (the shortest diameter) is approximately 12,714 km. The equatorial diameter (the longest diameter) is approximately 12,756 km. This is not a big difference, but it does make the Earth not quite a sphere.

Exaggeration of the bulging at the equator of the earth

Earths Formation 4.1

One Theory:-Early Molten Earth

-Denser Materials Sunk to the center

-Lighter Materials floated to the

outside

Inner Core• solid

• 6371 km from surface

• Radius about 1,100 km

Outer Core• liquid

• 5150 km from surface

• About 2400km thick

Mantle• solid with

liquid properties

• 5-65 km from surface

• 1500–3200 km thick

Crust• solid

• 0–65 km from surface

Layer Composition

Inner Core – Solid Iron NickelOuter Core –Liquid Iron NickelMantle – Iron, Silicon, MagnesiumCrust

Ocean Crust – BasaltContinental Crust - Granite

Lithosphere

The outer shell of the Earth consisting of the crust and uppermost portion of the mantle.

Asthenosphere

The partially melted layer of the mantle that underlies the lithosphere.

Crust

Mantle

Lithosphere

Asthenosphere

Rotation

The turning of a body, such as Earth, on its axis.

23.5°

Orbital plane

Effects of this rotation include the Coriolis effect, Foucault pendulum behavior, day and night, and sunrise and sunset.

standard time zones

Areas roughly defined by twenty-four 15° sections of longitude, each centered on a time meridian that establishes the hour of the day.

Begins at Prime Meridian

The prime meridian

SUNLIGHT

A time meridian

A standard time zone is 15° wide.

International Date Line

The imaginary line placed at roughly 180° longitude where the new calendar day begins, moving east to west.

revolution

The movement of one body around another, such as the Earth in its orbit around the sun.

parallax

The apparent shift in one object’s position relative to another caused by a change in the location of the observer.

summer solstice

The first day of summer in the Northern Hemisphere, which occurs on or about June 21 each year when the noon sun appears to reach its most northern point in the sky.

winter solstice

The first day of winter in the Northern Hemisphere, occurs on or about December 21 each year when the noon sun appears to reach its most southern point in the sky

Sun’s rays

vernal equinox

Start of spring in the Northern Hemisphere, occurring on or about March 21 each year when the noon sun is directly over the equator; one of two days each year when day and night are of equal length in both hemispheres.

autumnal equinox

Start of fall in the Northern Hemisphere, occurring on or about September 22 each year when the noon sun is directly over the equator; one of the two days each year when day and night are of equal length in both hemispheres.

Sun’s rays