- Distance wise from the Sun Earth occupies third position after Mercury and Venus and if we compare size of the eight planet of the Solar System then it occupies fifth position after Jupiter, Saturn, Uranus and Neptune. However in terrestrial planet it is the largest of all. There are few characteristics of terrestrial planets like:
- These planets lie in the first region of the Solar system. (regions of Solar system are Terrestrial planets, Gas giant Planets, Kupier belt, and Oort cloud region).
- Four Planets namely Mercury, Venus, Earth and Mars lies in the terrestrial region of the Solar system and are known as terrestrial planets.
- Terrestrial planets are made up of rocks and are highly dense.
- They have metallic cores.
- All terrestrial planets have volcanoes from which gases comes out during volcano eruption and with this gases atmosphere forms. Due to which all four terrestrial planets have their own atmosphere of different composition. Mercury which is very near to the Sun doesn’t have any atmosphere because pressure of Sun’s light and Solar flare pushes Mercury’s atmosphere into space. Mercury’s gravitational pull is also weak due to his small size; this adds another reason for Mercury’s having no atmosphere.
- Mercury and Venus which is nearer to the Sun is called interior planets.
- Distance from the Sun to the Earth in astronomy is referred as Astronomical Unit (AU) which is equal to 93 million miles or 150 million km.
- Earth is the densest planet among the solar planets. Its density is about 5.51 g/cm³.
- Earth suitability for existence of life on it: Physical conditions like Average Temperature and atmospheric pressure on the Earth are most suitable for existence of water on its surface and hence suitable for life. Moreover combination of Earth’s atmospheric Nitrogen, Oxygen and the Earth’s magnetic field protects its inhabitants from harmful solar radiation.
- Earth a Blue Planet: Due to the presence of water in liquid form in Earth’s large portion of 3/4th of its part it looks blue in colour from the space. Hence it is also called as blue planet of the Solar system.
- Earth’s twin: Venus, is considered as Earth’s twin because size, mass and density of Venus is almost equal to the Earth.
- Earth’s revolution: It revolves around the Sun in a elliptical orbit and completes one revolution around the Sun in 365.25 days.
- Shape of the Earth: Earth is not a perfect sphere however its shape is an oblate spheroid i.e., having a spherical shape which is flattened at the poles and oblates at the equator. This Oblation or bulging out at the equator is due to the rotation of the Earth. Because as the Earth rotates the centrifugal force causes object to move outward from the centre of gravity. Centrifugal force is largest at the equator hence it slightly bulges out at the equator making equator a great latitudinal circle with largest circumference and diameter. Geoid is the word which is used to denote the shape of the earth. Scientists have observed this fact by observing gravitational strength at the poles and equator. They observed that gravitational strength at the pole is greater than gravitational pull at equator. With this fact they have come to the point that equator is farther from the centre of the Earth than the pole which clearly indicates the bulging out shape of the Earth at the Equator. So weight of same object is more at pole than at equator. Some facts which clearly shows that Earth is slightly bulges out at the equator are mentioned below:
- Diameter of Earth from pole to pole is 12714 km
- Diameter of Earth at Equator is 12756 km
- Perimeter of the Earth pole to pole is 40008 km
- Perimeter of the Earth at Equator is 40075 km
- Earth’s Rotation: Earths rotates around its axis from west to east due to which sun rises in the east and sets in the west. There are only two planets in the Solar system which rotates from east to west they are Venus and Uranus. Hence on these two planets sun rises in the west and sets in the east. Earth’s rotational speed is highest at the equator and slowest at the pole. Hence centrifugal force is highest at the equator than any other point on the earth. One fact to be remember that though centrifugal force is highest at the equator however Coriolis force is zero at the equator and strongest at the pole. This Coriolis force is a force which acts on a moving object on a rotating system perpendicular to the direction of motion and perpendicular to the axis of rotation. This force is the main cause of deflection of moving winds towards right in the northern hemisphere and towards left in the southern hemisphere. Because this Coriolis force is zero at equator cyclones, hurricanes and tornadoes do not form between 5 degree N-S area.
- Solar & Sideral Day: When the duration of the earth’s rotation is calculated by measuring the time of crossing of Sun over a meridian twice is called solar day. It is 24 hours and Sideral day is calculated by calculating the time which is taken by earth for crossing a distant star over the meridian twice. It is 23 hours and 56 minutes and 4 seconds. Hence solar days are measured with respect to sun and sidereal days are measured in respect stars.
- Revolution of the Earth: Earth revolves around the sun in an elliptical orbit. Earth rotates around the sun with an average velocity of about 18.5 miles per second which is equal to 29.6 km/s. As we know that earth oribits around the sun in an elliptical orbit it is closest to the sun on about 3rd January and farthest to the sun on about 4th July. The position when earth is closest to the sun is called perihelion and the point when it is farthest is called aphelion.
- Tropical Year: The period of time from one vernal equinox to another vernal equinox is called tropical year. It is equal to 365.25 average solar days. For balancing this tropical year with calendar year one full day is added to the calendar after four year (Leap year).