- The Sun, the Moon and all other objects shining in the night sky are called Celestial Bodies.
- The moon, stars and planets cannot be seen during the daytime because the very bright light of the Sun does not allow us to see them.
- Stars are celestial bodies that are very big and hot. They are made up of gases. They have their own heat and light, which they emit in large amounts. The Sun is also a Star.
- Countless twinkling stars in the night sky are similar to the Sun. But we do not feel their heat or light, and they look so tiny because they are very far from us.
- Constellations are various patterns formed by different groups of stars. For example,Ursa Major or Big Bear.
- The Saptarishi constellation is a group of seven stars that forms a part of Ursa Major constellation.
- The North Star indicates the north direction. It is also called the Pole Star. It always remains in the same position in the sky. We can locate the Pole Star with the help of Saptarishi.
- If an imaginary line is drawn joining the pointer stars and extended further, it will point to the Pole Star.
THE SOLAR SYSTEM
- The Sun, eight planets, satellites and some other celestial bodies known as asteroids and meteoroids form the Solar System.
- The Sun is in the centre of the solar system. It is huge and made up of extremely hot gases.
- It provides the pulling force that binds the solar system.
- It is the ultimate source of heat and light for the solar system.
- It is about 150 million Km away from the Earth, so its tremendous heat is not felt so much by us.
- Planets are celestial bodies that do not have their own heat and light. They are lit by the light of the stars. Earth is a planet too. It gets all its heat and light from the Sun, our nearest star.
- There are eight planets in our Solar System- Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
- Mercury, Venus, Earth and Mars are very close to the sun and are made up of rocks. They are called Inner Planets.
- Jupiter, Saturn, Uranus and Neptune are very far away from the sun and are made up of gases. They are called Outer Planets.
- Jupiter, Saturn and Uranus have rings around them. These are belts of small debris.
- The planets move around the Sun in fixed, elongated paths called Orbits.
- Mercury, being the nearest planet to the Sun, takes only around 88 days to complete one round.
- Venus is considered as ‘Earth’s twin’ because its size and shape are quite similar to that of Earth.
- Till the year 2006, Pluto was also considered a planet. But then it was demoted to the status of a ‘dwarf planet‘.
- It is the fifth largest planet by size and is slightly flattened at the poles.
- Its shape is described as a Geoid which means an Earth-like shape.
- It is a unique planet in the Solar System because:
- Conditions favourable to support life are probably found only on the earth.
- It is neither too hot nor too cold.
- It has water and air, which are very essential for our survival.
- The air has life supporting gases like oxygen.
- From the outer space, the Earth appears blue because its two-thirds surface is covered by water. It is, therefore, called a blue planet.
- It is a celestial body that moves around the planets in the same way as the planets move around the sun.
- A human-made satellite is an artificial body. It is designed by scientists to gather information about the universe or for communication.
- It is carried by a rocket and placed in the orbit around the earth.
- The Moon is a satellite and moves around the Earth.
- The only satellite of Earth.
- Its diameter is only one-quarter that of the earth.
- It appears so big because it is nearer to Earth than other celestial bodies.
- It moves around the Earth in about 27 days and takes exactly the same time to complete one spin. Hence, only one side of the moon is visible to us on the earth.
- It does not have conditions favourable for life like water or air.
- It has mountains, plains and depressions on its surface.
- The moon appears at different times, in different shapes and at different positions.
- The Full Moon can be seen only once in about a month’s time on the Full Moon night or Poornima.
- A fortnight later, it cannot be seen at all. It is the New Moon night or Amavasya.
- These are numerous tiny bodies which also move around the Sun-like stars, planets and satellites.
- They are found between the orbits of Mars and Jupiter.
- These are small pieces of rocks which move around the Sun.
- Sometimes they come near the earth and tend to drop upon it.
- During this process due to friction with the air, they get heated up and burn, causing a flash of light.
- Sometimes, a meteor without being completely burnt falls on the earth and creates a hollow.
- It is a huge system of billions of stars, and clouds of dust and gases.
- Our Solar System is a part of the Milky Way galaxy.
- Millions of such galaxies make up the Universe.