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• Star: Twinkling objects in the night sky
• Planets: Non twinkling objects in the night sky
• Celestial objects: Stars, planets, moon and other objects in the sky
• Full moon day: When full disc of the moon is visible in the sky
• New moon day: When the moon is not visible in the sky
• Crescent moon: Moon appearing partially in the sky on next day of new moon day.
• Moon:
  • Moon does not have its own light. It is visible due to the reflection of sunlight.
  • Different shapes of the moon is visible only because only that part of the moon reflects the sunlight.
  • Surface of moon is dusty and barren
  • Moon has large craters and large number of mountains
  • No air and water is present on moon
  • No life exist on the moon
• Light year: Distance travelled by light having speed on 3,00,000 km/s during one year
• Constellations: The stars forming a group that has a recognisable shape


Constellation: Ursa Major, Orion, Cassiopeia

• Ursa Major:
  • Also known as Great Bear, Saptarishi or Big Dipper
  • Seven stars present in the constellations
  • Appears like a question mark or a ladle
• Orion:
  • Also known as Hunter
  • Seven stars present in the constellations
  • The three middle stars forms the belt of the hunter. The four bright stars of constellations appear to be a quadrilateral.
• Cassiopeia:
  • Appears like distorted letter W or M
  • Located in the northern sky during early night of winter

Click here to watch video on Constellations In The Night Sky

• Our solar system:
  • Solar system is made of sun and celestial bodies revolving around it.
  • Sun is the nearest star for all planets, which continuously emits heat and light
  • There are 8 planets in our solar system. They are Mercury, Venus, Earth, Mars , Jupiter, Saturn, Uranus and Neptune
  • Inner planets: Mercury, Venus, Earth, Mars
  • Outer planets: Jupiter, Saturn, Uranus, Neptune
  • Orbit: Fixed path in which planets revolve around the sun
  • Period of revolution: Time required to complete one revolution in an orbit
  • Period of rotation: Time taken by a planet to complete one rotation around itself
  • Satellites: Celestial body to orbit around the earth or any other planet. Eg. Moon is a natural satellite of earth.
• Planets in our solar system:
  • Mercury: Nearest planet from sun. It can be observed during sunrise and sunset, as the rest of the time it is not visible due to the glare of the sun.
  • Venus: Nearest planet from the earth. Before sunrise it appears in eastern sky, therefore it is called morning star. After sunset is appears in western sky, therefore, it is called evening star.
  • Earth: It is the only planet having life, this is because of good temperature range, presence of water and the favourable atmosphere along with ozone layer. Earth appears blue green from the space. Axis of earth is slightly tilted which is responsible for variations in seasons. Moonis the natural satellite whereas, other satellites are artificial satellites made by man.
  • Mars: Mars appears red therefore known as red planet. Mars has two natural satellites.
  • Jupiter: It is largest planet. Jupiter is 1300 times larger and 318 times heavier than earth. Jupiter has many number of natural satellites revolving around it.
  • Saturn: It is yellow planet with beautiful rings and have a large number of natural satellites. Density of saturn is lowest. Its density is lower than water.
• Asteroids: In between Mars and Jupiter large number of objects revolving around sun are asteroids.
• Comets: Comet is an object with bright head with long tail. E.g. Halley’s Comet appears every 76 years.
• Meteors ( Shooting star ): these are not stars but the random objects having thin, long and bright light.
• Meteorites: When meteors reaches Earth are called as meteorites.
• Artificial satellites: Man made satellites revolving around the earth. E.g. INSAT, IRS, Kalpana-1, EDUSAT, etc.