What is the universe? Give the unit to measure the distance between any two heavenly bodies.

The family of sun, including all planets and their satellites, meteors, comets, asteroids, etc. is called the solar system.
We know,
        Speed of light = 3 x 10⁸ m/s.
        Time = 1 year.
We have,
Distance travelled by light in 1 year = speed of light * time
                                         ...

Planets are the heavenly bodies which revolve around the sun in elliptical orbits.
Those planets which are present inside the asteroid belt are called inner planets.
Those planets which are present outside the asteroid belt are called outer planets.

The rocks and metal objects which are present in between the orbits of Mars and Jupiter that revolve around the sun are called asteroids or minor planets.

The pieces of stone or metal which enters the earth's atmosphere are called meteors.
A meteors lasts for very short time and completely finished in atmosphere because the small rock pieces burn and vaporize completely due to the excessive heat produced by the atmospheric friction.

The big meteors which do not burn completely and reach the surface of the earth are called meteorites.
Its types are:
        - Stony meteorites.
        - Iron meteorites.
        - Stony iron meteorites.

Any three purposes of launching artificial satellites are:
        - For the communication of radio, TV and telephone signals across the world.
        - For weather forecasting.
        - To study space and different regions of earth.
        - For the study of cosmic rays and solar radiation.
        - For spying or military purposes.

A galaxy is a vast system of stars, dust particles and gases isolated from a similar system in space.
Its types are:
        - Spiral galaxies.
        - Elliptical galaxies.
        - Irregular galaxies.

Our solar system is situated on Milky-way galaxy.
It has the spiral shape.

A group of stars in the sky which resemble the animal, god or materials is called a constellations.
Any four constellations are:
        - Ursa major.
        - Ursa minor.
        - Orion.
        - Cassiopeia.

A broom shaped shining object with a bright head is called a comet.
When a comet approaches the sun, some of its frozen matter begins to evaporate into gases due to the heart of the sun. These gases rush out by rapid vaporization in the form of jets carrying solid particles with them. In this way, a long tail of a comet is formed due to the motion of comet and effect of the solar wind. Therefore, the tail of a comet become longer as it approaches...

A fast moving star radiating radio frequency is called pulsar.
The star can't be seen but sends out regular rapid radio signals.

According to Big Bang theory, all the matter in the universe was originally concentrated in one vast lump called a primeval atom. About 15 billions years ago, this super dense and extremely hot body having neutrons and protons exploded with Big Bang and all the matter started flying in all directions through space leading to the formation of galaxies and other heavenly bodies.

a.    Synodic month and sidereal month.

b.    Asteroids and planets.

We all know, both earth and mars revolve around the sun in a fixed orbit. They have the specific numbers of satellites that revolves around them. So earth & mars are called planets.

Though there is the presence of water, oxygen, carbon dioxide on both Earth and Venus, life is not possible in Venus because its surface temp. is very high (about 865f) which is not suitable for the survival of living beings. But the temp. of earth is favorable for living beings. So, life is possible on Earth but not on Venus.

Pluto has been removed from the list of planets because:
        - The size of the Pluto is very smalt compared to the average size of other planets.
        - The orbit of Pluto coincide with orbit of Neptune.
        - The orbit of Pluto doesn't lies on the same plane to the plane of other planets.

When a comet approaches the sun, some of its frozen matter begins to evaporated into gases due to the heat of the sun. These gases rush out by rapid vaporization in the form of jets, carrying solid particles with them. In this way, a long tail of comet is formed due to the motion of the comet and effect of solar wind.

The tail of the comets are made up of ice and dust particles. When the comet comes closer to sun, the ice vaporizes and a long tail is formed due to high speed of comet. But when the comet moves away from the sun, the ice doesn't vaporizes due to low temp. and finally tail disappears.

We know, star are the luminous huge heavenly bodies with very strong gravitational force. But the comet are the non-luminous small object revolving around the sun with very less gravitational force. So, comet is not actually a star.

A meteor lasts only for a few minutes because the small rock pieces burn and vaporize completely due to the excessive heat produced by atmospheric friction.

Neptune: Planet
Milky Way: Galaxy
Venus: Planet
Enke: Comet
Andromeda: Galaxy
Phobes: Satellite
Ursa major: Constellation
Titan: Satellite

Ursa Major is seen in summer season in northen sky.

The twelve special constellations of solar path are called zodiacs.
Any three examples are:
        - Aries.
        - Cancer.
        - Leo.
        - Pisces.

Any three superstitions about zodiacs are: 
        - Astrologers match the zodiacs and stars of the bridge and groom before marriage.
        - There is no scientific evidence about travel and starting work according to the zodiac, names and days.
        - Astrologers believe that the nature and behavior of a person differ according to his/her zodiac.

The heavenly bodies that have their own sources of light are called stars.
Any two features of stars are:
        - They are luminous.
        - They consists of hydrogen, helium and dust particles.