Beyond Earth

When we look up at the sky, we see many objects — the Sun by day, and the Moon and countless stars by night. All the natural objects in the sky are called celestial bodies (or heavenly bodies).

• Stars — huge balls of hot, glowing gas that make their own light and heat. They look like tiny points because they are extremely far away. The Sun is also a star — the nearest one to us.
• Planets — large bodies that move around the Sun. They do not make their own light; they shine by reflecting sunlight. Earth is a planet.
• The Moon — a natural satellite that moves around the Earth. It also has no light of its own and shines by reflecting the Sun’s light. Its changing shapes through the month are called phases.

Stars appear to twinkle because their light passes through the moving air of our atmosphere, while planets, being much closer, usually shine steadily without twinkling. Groups of stars that seem to form a pattern or picture are called constellations (for example, Orion and the Great Bear, Saptarishi). The Pole Star appears almost fixed in the north and has helped travellers find direction for centuries.

The Sun and the family of bodies that move around it together form the solar system. The Sun is at the centre and is by far the largest member; its gravity holds all the other bodies in their paths. The Sun gives us light and heat and is the main source of energy for life on Earth.

Eight planets move around the Sun along fixed paths called orbits. In order of distance from the Sun they are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Mercury is the closest and Neptune the farthest. Jupiter is the largest planet, and Earth is the only planet known to support life, because it has the right temperature, water and air.

The solar system also contains smaller members:

• Satellites (moons) — bodies that move around planets, like our Moon.
• Asteroids — small rocky bodies, most found in a belt between Mars and Jupiter.
• Comets — icy bodies that develop a bright, glowing tail when they come near the Sun.
• Meteors — ‘shooting stars’; bits of rock that burn up brightly as they enter Earth’s atmosphere.

For thousands of years people could only watch the sky. Today we can study it closely and even travel into space. Space exploration is the study of outer space using telescopes, satellites and spacecraft.

• A telescope is an instrument that makes faraway objects in the sky look bigger and clearer, so we can study stars and planets.
• A rocket is a powerful vehicle that carries spacecraft and satellites into space by overcoming the Earth’s gravity.
• An artificial satellite is a human-made object placed in orbit around the Earth. Satellites help with weather forecasting, television and phone signals, the internet, and finding our location (navigation).
• An astronaut is a person trained to travel and work in space.

India’s space agency is the Indian Space Research Organisation (ISRO). It has launched many satellites and famous missions such as Chandrayaan to the Moon and Mangalyaan to Mars. In 1969, humans first walked on the Moon. Robotic vehicles called rovers now drive across the surface of other worlds, like Mars, to explore them. Space exploration helps us understand the universe and brings many useful technologies into everyday life.