⦁ Earth is almost spherical in shape.
⦁ It’s diameter is about 12000km.
⦁ Earth rotates on its axis.
⦁ The axis around which earth spin is an imaginary line through the center of the planet from the north pole to the south pole.
⦁ Earth has seasons because it’s axis is tilted.
⦁ Earth is considered as the fifth- largest planet in the solar system.
⦁ It is the third- closest planet to the sun
⦁ Earth orbits the sun once every 365 days, or one year.
⦁ It’s average distance is 150 million km from the sun. This distance is termed one Astronomical Unit(AU).
⦁ Below Earth’s surface are layers of rock and metal. Temperature increases with depth, all the way to about 12,000 degrees Farenhite at earth’s inner core.
⦁ Earth consists of land, air,water and life. This land contains mountains, valleys and flat areas. The air is made up of different gases, mainly nitrogen and oxygen. The water includes lakes, oceans, rivers, streams, rain, snow and ice. Life consists of people, animals and plants.
⦁ From space, earth looks like a blue marble with swirls and areas of brown, yellow, green and white.
⦁ The blue is water, the white is swirls are clouds. The areas of brown, yellow and green are land. And the areas of white are ice and snow volcanoes and their smoke.
⦁ Artificial satellites helps scientists predict waether and climate. It also helps public health officials track diseases and famine.
⦁ It helps farmers decide when to plant crops and what kinds of plants. And helps emergency workers respond to natural disasters.
⦁ Areas facing the sun experience day time and areas away from the sun experience night. The north pole and south pole have continuous daylight or darkness depending on the time of year.
⦁ Earth is studied using artificial satellites which look at earth from space.
THE NIGHT SKY
The patterns in the sky have inspired many design markers and poets.
⦁ Clear moonless night in a place far away from the city is best for watching the sky.
⦁ There are hundreds of twinkling stars and moon in the night sky.
⦁ They are distributed all over the sky.
⦁ We see many recognisable patterns of stars.
⦁ There are star-like objects which do not twinkle.
⦁ Occasionally, streaks of light which give the impression of falling stars.
⦁ Objects which shine but do not twinkle are planets.
⦁ Their paths are not uniform.
⦁ Seemingly wandering motion they were called wanderers.
⦁ Stars twinkle but planets do not.
⦁ Stars are self luminous but planets are not.
⦁ Size of a star compared to planets is large.
⦁ They appear small because of their enormous distance from the earth.
⦁ Only four planets are visible to naked eyes. They are Venus, Mars, Jupiter and Saturn.
⦁ We can be able to observe another planet Mercury just before sunrise and just after sunset if the sky is clear.
THE CELESTIAL SPHERE
⦁ Any shining object in the night appears to be located on a huge sphere.
⦁ We appear to be the center of the sphere.
⦁ Objects on celestial sphere are called celestial objects. Direct observations show that most of the celestial objects appear to move from east to west. This observation made many people think that we are at the centre and the universe and all celestial objects move around us.
⦁ The earth was considered as the center of the universe and all other celestial objects moving around us. This model is called ‘Geocentric model’.
⦁ The Geocentric model was not able to explain the changing brightness and the variation in the path of planets.
⦁ Nicholas Copernicus proposed an alternative model called ‘Heliocentric model’. He placed the sun at the center of the observable Universe around which other celestial objects including the earth would revolve.
⦁ Later Galileo Galilee provided scientific evidence for this model by his observations with the telescope. And Johannes Kepler showed that paths of the planets around the sun are elliptical.
⦁ Indian Astronomer Neelakanta Somayaji based on a suggestion of his teacher “Parameshwara” had proposed a model similar to the ‘ Heliocentric’ model. Development of the telescope and mathematical calculation based on gravitational laws by Issac Newton helped to get a better understanding of the movement of planets around the sun.
THE SOLAR SYSTEM
⦁ Solar system is a very small part of the entire universe.
⦁ It has one star that is ‘ sun’ at the centre and planets and other objects moving around it
⦁ The sun is at the centre of the solar system.
⦁ Apart from the planets which are visible to the naked eye namely- Mercury, Venus, Mars, Jupiter and Saturn, there are two more- Uranus and Neptune-which can be seen by a telescope.
⦁ The Asteroid belt between the orbit of Mars and Jupiter.
⦁ Dwarf planet like Pluto, Ceres, Eris and others.
⦁ Satellites of the planets which are also called the moon of the planets.
⦁ Comets such as Halley.
⦁ Artificial objects like satellites and spacecrafts.
⦁ Sun is the centre of the solar system.
⦁ It has radius which is 109 times that of the earth.
⦁ This means it would take 13 lakh earth’s to fill the sun.
⦁ It consists mainly of hydrogen and helium.
⦁ The reaction in the sun release enormous amount of energy.
⦁ A part of energy is received by the earth in the form of heat and light.
⦁ Life on Earth is sustained by this energy.