Samacheer Class 6 Social Science - The Universe and Solar System

The planets in our solar system can be broadly classified into inner and outer planets, with distinct characteristics. The inner planets, also known as terrestrial planets, include Mercury, Venus, Earth, and Mars. They are relatively small in size, primarily composed of solid rock and metals, and possess dense structures. Their surfaces are often marked by features like mountains, volcanoes, and impact craters, and they generally have few or no moons and no ring systems. In contrast, the outer planets, referred to as Jovian or gas giants, comprise Jupiter, Saturn, Uranus, and Neptune. These planets are significantly larger in size and are predominantly composed of gases like hydrogen and helium, with smaller rocky cores. A notable feature of the outer planets is the presence of extensive ring systems, and they possess numerous moons.

Effects of Rotation:
It is the spinning movement of the Earth on its axis
The time taken by the Earth to complete one rotation is called a day.
The rotation of the Earth causes day and night, As the Earth is spherical in shape, only one half of it is illuminated by the Sun at a time.
The other half remains dark.
The illuminated portion of the Earth experiences day, whereas the darkened part of the Earth experiences night.
Effects of Revolution:
It is the movement of the Earth around the Sun on its elliptical path.
The Earth takes 36514 days to complete one revolution.
It revolves around the Sun at a speed of 30 km per second.
The remaining quarter day is added once in every four years in the month of February.
The inclination of the Earth on its axis and its revolution around the Sun cause different seasons.

Earth is the most suitable planet to support life. It has three major components that we call the realms of the Earth lithosphere, hydrosphere, and atmosphere.
(i) Lithosphere: The word lithosphere is derived from the Greek word Lithos, which means rocky. The Lithosphere is the land on which we live.
(ii) Hydrosphere: The word Hydro means water in Greek. The hydrosphere consists of water bodies such as oceans, seas, rivers, lakes, ice caps on mountains, and water vapour in the atmosphere.
(iii) Atmosphere: The word Atmo means the air in Greek. The atmosphere is the envelope of air that surrounds the Earth. Different types of gases make up the atmosphere. The major gases are Nitrogen (78%) and Oxygen (21%).
(iv) Biosphere: The narrow belt of interaction among the lithosphere, the hydrosphere, and the atmosphere, where life exists is known as Biosphere. Bio means life in Greek. It consists of distinct zones.
J. Picture Study

Mercury is the closest planet to the Sun. Jupiter is the largest planet in our solar system. Neptune is the farthest planet from the Sun. Mars is the second smallest planet. These facts about our solar system help us understand the arrangement and characteristics of the eight planets that orbit around the Sun. Mercury, being closest to the Sun, experiences extreme temperatures and has a rocky surface. Jupiter, the largest planet, is a gas giant composed mainly of hydrogen and helium. Neptune, located at the outer edge of our solar system, is an ice giant with strong winds. Mars, known as the red planet due to iron oxide on its surface, is smaller than Earth but larger than Mercury, making it the second smallest among the eight planets.

The planet identified in the picture is Uranus. The colour of Uranus is green or blue-green. Uranus appears in this distinctive colour due to the presence of methane in its atmosphere. Methane absorbs the red light from the Sun and reflects the blue and green wavelengths, giving the planet its characteristic appearance. Uranus is an ice giant located in the outer region of our solar system, far from the Sun. It is unique among the planets because it rotates on its side, meaning its axis of rotation is tilted at an extreme angle compared to other planets. This unusual orientation may have resulted from a collision with another celestial body early in the formation of the solar system. Uranus has a system of rings and several natural satellites orbiting around it, making it an interesting subject of astronomical study.