Question

Visit the sites of the institutes ISRO (www.isro.gov) and NASA (www.nasa.gov) and collect information about the various celestial bodies in the solar system and universe, and discuss the same in the class.

Answer 1

Celestial bodies are objects present in space.

Celestial bodies in the solar system

1. Sun: A yellow star at the centre. Its surface temperature is about $$6000^\circ\mathrm{C}$$. It has a huge gravitational force, so planets, asteroids, comets and other bodies revolve around it.
2. Planets: There are eight planets.
   • Mercury: Closest to the Sun and the fastest-moving planet. Its surface has many craters.
   • Venus: Brightest and hottest planet. It rotates from east to west.
   • Earth: Third planet. It has life, one moon and a magnetic field.
   • Mars: Red Planet. It has the largest mountain, Olympus Mons.
   • Jupiter: Largest planet. It is called the stormy planet.
   • Saturn: Sixth planet. It has bright rings and very low density.
   • Uranus: Seventh planet. Its axis is greatly inclined, so it looks like it is rolling on its orbit.
   • Neptune: Eighth planet. It has a deep blue colour and very high-speed winds.
3. Satellites: Bodies that revolve around planets. Earth has 1 moon; Mercury and Venus have 0; Mars has 2; Jupiter has 64; Saturn has 33; Uranus has 27; Neptune has 13. Earth's Moon has no atmosphere.
4. Asteroids: Small rocky bodies found mostly in the belt between Mars and Jupiter.
5. Comets: Bodies of ice, frozen matter and dust. They form a tail when near the Sun. Long-period comets take more than $$200,\text{years}$$ to revolve; short-period comets take less than $$200,\text{years}$$ to revolve. Halley's comet takes $$76,\text{years}$$ to revolve.
6. Meteors and meteorites: Rocky pieces that burn in the atmosphere are meteors; they look like falling stars. Those reaching the Earth are meteorites. The Lonar Lake in Maharashtra is believed to be formed by a meteorite.
7. Dwarf planets: Small bodies revolving around the Sun. Pluto is a dwarf planet.

Celestial bodies in the universe

1. Stars: Huge glowing objects made of gases. Their surface temperature ranges from 3500°C to 50000°C. Blue stars are hotter than red stars.
2. Types of stars: Sun-like stars, red giants, supernovae, binary stars and variable stars. Red giants are much bigger than the Sun. Binary stars are two stars revolving around each other. Variable stars, like Polaris, change in brightness.
3. Nebulae: Clouds of dust and gases where new stars are born.
4. Star clusters: Groups of stars found in galaxies. Dead stars and newly born stars are also found in the Milky Way.
5. Galaxies: Large groups of innumerable stars and their planetary systems. The Milky Way is our galaxy. Andromeda is the nearest galaxy to the Milky Way. The Milky Way is in the Local Group of galaxies. Galaxies are spiral, elliptical, barred spiral or irregular.
6. Universe: It contains innumerable galaxies, space between them, stars, planets, gases, dust, nebulae and energy.