Size shape and motion

Earth size

EARTH SIZEEarth is largest of

the terrestrial planets. its volume is also is also the

largest. Chemically , Earth is composed of 34.6%

Iron, 29.5 % Oxygen, 15.2% Silicon, 12.7%

Magnesium, 2.4% Nickel, 1.9 Sulfur

and 0.05% Titanium

EARTH SHAPE

Earth shape is not really a perfect sphere. It has bulges in the center or around the equator. This bulging effect is due to the rotation of the earth, and with this bulge the Earth is described as having a shape of oblate spheroid

Motion of the earth

The equatorial bulge at at Earth’s Equator is

measured at 26.5 miles and caused by the

Earth’s rotation and gravity

The equatorial bulge at at Earth’s Equator is measured at 26.5 miles and caused by

the Earth’s rotation and gravity. According to Tiller (2005) there are three motion that are independent of motion of

the Sun and the galaxy

1. A yearly revolution around the sun 2. A daily rotation on its axis 3. A slow clockwise wobble of its axis

Earth has three different kinds of motion:

1

•Rotation

2

•Revolution

3

•Precession

Rotation

> is the movement of the earth as it rotates from west to east on its axis . Earth’s rotation appears to rise from the east moves to west.

Earth’s rotation can be measured in two ways:

1. Near solar day – it is the time interval from one noon to the next noon day because it’s the time when the sun has reached its highest point in the sky

2. Sidereal day – it is the time which takes the earth to make one complete rotation with respect to a star other than the sun. The earth rotates 360 degree in 24 hours or 15 degree per hour

Revolution

> Revolution is one

complete orbit of the Earth to the Sun, in about 365.25 days. The direction of revolution is counter clockwise as viewed down from the north

Earth orbit can be classified in two ways:

1. Perihelion – It is the point in which the earth is closer to the sun, and It is the time where the earth moves fastest this usually happens during summer season.

2. Aphelion – It is the point in which the earth is farthest to the sun, and it is the time where the earth moves slowest, this usually happens during rainy season.

Precession > is the reaction of earth to the gravitational pull of the

moon and the sun on its equatorial bulge, however, the results in a slow wobbling of the earth as it turns on its axis.

Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In other words, the axis of rotation of a precessing body itself rotates around another axis. A motion in which the second Euler angle changes is called nutation. In physics, there are two types of precession: torque-free and torque-induced.