Comets

• Comets are small pieces of ice and dust that orbit around the Sun, but their paths are not like those of the planets.
• Most comets spend much of their time out of the Solar System, beyond Pluto. However, they can enter new orbits that bring them into the Solar System where they become visible from earth.
• The most famous comet is called Halley’s comet which returns to the center of the Solar System every seventy-six years.
• Every comet has a head and a long tail. The small solid part at the center of the head is called the nucleus.
• The nucleus contains ice and the heat of the Sun causes the ice to melt and give out gas and dust.
• The gas and dust given out from the head of the comet forms the tail. The gas gives out light.
• The tail of the comet always points away from the sun.

Asteroids

• Besides the nine planets there is also asteroid belt.
• The asteroid belt lies between the orbits of Mars and Jupiter.
• Asteroids are small pieces of rocks mixed with metals orbiting round the Sun.
• Asteroids vary in size. Some can be as small as dust particles while some can be a few hundred kilometers in diameter.

 

Natural Satellites

• Natural satellites are the natural objects which orbit around planets.
• The Moon is the Earth’s only natural satellite.
• All the planets in the Solar System have natural satellites expect Mercury and Venus.
• The number of natural satellites is shown below. 

What is Universe?

The universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature.