Earth - A Place to Call Home
Earth is known for its green and blue appearance. The radius of Earth is 3,959 miles, and its mass is 5.972E24 kg. There is one moon, and Earth is known for its vast oceans.
The seasons are caused as the Earth, tilted on its axis, travels in a loop around the Sun each year. Summer happens in the hemisphere tilted towards the Sun, and winter happens in the hemisphere tilted away from the Sun. As the Earth travels around the Sun, the hemisphere that is tilted towards or away from the Sun changes.
Rotation is when a planet or moon turns all the way around or spins on its axis one time. The axis of rotation is an imaginary line going from the north pole to the south pole. When a planet or moon travels once around an object this is considered a revolution. On Earth, a rotation is pretty short - it happens once a day! It is the rotation that makes the sun appear to come up in the morning and set at night. On Earth, a revolution is quite a bit longer - one year!
In nuclear physics, nuclear fusion is anuclear reaction in which two or more atomic nuclei come very close and then collide at a very high speed and join to form a new nucleus. During this process, matter is not conserved because some of the matter of the fusing nuclei is converted to photons (energy)
Why is everything spherical? It all comes down to gravity. All the atoms in an object pull towards a common center of gravity, and they’re resisted outwards by whatever force is holding them apart. The final result could be a sphere… but not always, as we’re about to learn.
A light year is a unit of astronomical distance equivalent to the distance that light travels in one year, which is 9.4607 × 1012 km (nearly 6 trillion miles).
Gravity is responsible for the formation of the solar system.
Earth is the only planet whose English name does not derive from Greek/Roman mythology. The name derives from Old English and Germanic. There are, of course, hundreds of other names for the planet in other languages. In Roman Mythology, the goddess of the Earth was Tellus - the fertile soil (Greek: Gaja, terra mater - Mother Earth).
It was not until the time of Copernicus (the sixteenth century) that it was understood that the Earth is just another planet.
Earth, of course, can be studied without the aid of spacecraft. Nevertheless it was not until the twentieth century that we had maps of the entire planet. Pictures of the planet taken from space are of considerable importance; for example, they are an enormous help in weather prediction and especially in tracking and predicting hurricanes. And they are extraordinarily beautiful.