Mercury is a dead planet and the most heavily cratered object in the solar system. It is a world of black starry skies, gray craters, no moon and not enough gravity to hold an atmosphere.

Later, Heraclides (330 B.C.) developed the first Solar System model, placing the planets in order from the Earth it was is now called the geocentric solar system model and the beginning of the geocentric versus heliocentric debate.

Galileo

Venus is very similar to Earth in size and mass – and so is sometimes referred to as Earth’s sister planet – but Venus has a quite different climate. Venus’ thick clouds and closeness to the Sun (only Mercury is closer) make it the hottest planet – much hotter than the Earth.

The idea of a second sun in our solar system is not as bizarre as it might sound. Binary star systems (two stars orbiting the same center of mass) are quite common. In fact, Alpha Centauri, our solar system’s nearest neighbor, is a binary system.

The name “Earth” is derived from both English and German words, ‘eor(th)e/ertha’ and ‘erde’, respectively, which mean ground. One interesting fact about its name: Earth is the only planet that wasn’t named after a Greek or Roman god or goddess.

Layers of the atmosphere: troposphere, stratosphere, mesosphere and thermosphere. Earth’s atmosphere has a series of layers, each with its own specific traits. Moving upward from ground level, these layers are named the troposphere, stratosphere, mesosphere, thermosphere and exosphere.

Sol

ellipsoid

Many people think that the Earth is perfectly round; however, it is actually pear shaped! The top pushes in while the bottom bulges out. The southern hemisphere is slightly larger than the northern hemisphere, giving the odd pear shape. The poles are also slightly flattened.

The geoid is a shape like the surface of the Earth. For many practical purposes, a simpler shape is used because that makes calculations easier. That shape is called a reference ellipsoid. In basic education, the shape of the Earth is described as being like an orange, a sphere but wider round the equator.

The oblate spheroid, or oblate ellipsoid, is an ellipsoid of revolution obtained by rotating an ellipse about its shorter axis. It is the regular geometric shape that most nearly approximates the shape of the Earth. A spheroid describing the figure of the Earth or other celestial body is called a reference ellipsoid.

The geoid (/ˈdʒiːɔɪd/) is the shape that the ocean surface would take under the influence of the gravity and rotation of Earth alone, if other influences such as winds and tides were absent. This surface is extended through the continents (such as with very narrow hypothetical canals).

A geoid is the irregular-shaped “ball” that scientists use to more accurately calculate depths of earthquakes, or any other deep object beneath the earth’s surface. If Earth were a perfect sphere, calculations of depth and distances would be easy because we know the equations for those calculations on a sphere.

The geoid is defined as the surface of the earth’s gravity field, which is approximately the same as mean sea level. It is perpendicular to the direction of gravity pull. A spheroid is a three-dimensional shape created from a two-dimensional ellipse. …

The geoid approximates mean sea level. The shape of the ellipsoid was calculated based on the hypothetical equipotential gravitational surface. A significant difference exists between this mathematical model and the real object.

More accurately, the Earth is an ellipsoid, sometimes referred to as a spheroid. While ellipsoids are round and smooth like spheres, they are not symmetrical when divided in all directions.

The easiest way this may be calculated is by selecting a location and calculating the mean sea level at that point and use it as a datum. For example, a period of 19 years of hourly level observations may be averaged and used to determine the mean sea level at some measurement point.

Planet Earth has been called the “Blue Planet” due to the abundant water on its surface. Here on Earth, we take liquid water for granted; after all, our bodies are mostly made of water. However, liquid water is a rare commodity in our solar system. Liquid water covers most of the surface of our planet.