PLANET EARTH
Earth is solid, spherical, rocky body with oceans and an atmosphere. It is unique in our Solar system because it has large amounts of surface water, an oxygen containing atmosphere, a temperate climate, and living organisms. It is an oblate spheroid, not a perfect sphere, so shaped due to its rotation on its axis. The average diameter is 12,900 km., with that at the equator being about 43 km. greater than that at the poles. An exercise in finding the diameter of the Earth as done by Eratosthenes, a Greek mathematician and astronomer is explained below. Click.
The Earth has three motions.
1. Rotation about its own axis, a complete rotation every 24 hours. We can prove that the earth rotates using a "Foucault" pendulum. This experiment works best at the poles although results could be obtained anywhere except at or very close to the equator.
For Details of the Pendulum and its operation click below.
2. The second motion is the revolution of the Earth around the Sun. Earth revolves eastward around the Sun and sweeps out a plane called the orbital, or ecliptic plane. This motion of the Earth produces an apparent annual westward motion of the Sun. This takes 365 days, 5 hours, 48 minutes, and 46 seconds or 365.2422 days. This can be proved using Stellar Parallax. Parallax of a star is the apparent displacement of a nearby star with respect to more distant stars. For a more complete explanation with a figure, click below.
3. The third motion is Precession of the Earth's axis. The Earth's axis is presently pointing toward the star Polaris, also known as North or Pole star. In approximately 12,000 years, the axis will be pointing toward the star Vega in the constellation Lyra. The Earth wobbles like a top, the period of precision being 25,800 years. This is called a Platonic Year. For a more detailed explanation with a figure click below.
For another explanation, click below
For other motions of the Earth, click here: Earth's movemnets
The fraction of the incident sunlight reflected by an object is called its albedo. Earth's albedo is 0.33. It reflects more light because the clouds and water areas are good reflectors. As a comparison, the moon has a albedo of 0.07, while Venus has one of 0.76. For more details about Albedo, click here: Albedo
Milutin Milaankovitch predicted two other movements of the earth.
1.Variations in the Earth's orbital eccentricity—the shape of the orbit around the sun.
2.Changes in obliquity—changes in the angle that Earth's axis makes with the plane of Earth's orbit.
For details of the Earth click below
Details of Earth
Details of Earth
For more information of the Earth's movements: Earth's Movements
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