Constellation

The stars which appear in the form of closed groups and forms recognizable shapes and patterns, are known as constellation. There are 88 constellation known so far. Out of them, twelve constellations are considered as sign of zodiac. These are Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Sagittarius, Scorpio and Aquarius. Some of the important constellation are:

1. Ursa major
2. Ursa minor
3. Orion
4. Scorpio
5. Pledies
6. Cassiopeia

1. Ursa major constellation

It contains seven bright stars arranged in the form of a big spoon. It is called the Big Dipper. This name is derived from the word "dipper" which in olden days used to mean a large spoon used for drinking water. It is also called the Great Bear because, along with several other fainter stars, it forms the picture of a bear The Nepali name of Ursa Major constellation is Saptarishi.

2. Ursa minor

This is also a group of seven bright stars similar to the Ursa Major. The pole star, a star that is visible towards the north and always remains stationery in the sky, is a part of this constellation. This, Ursa Minor constellation is also known as little bear constellation. This is less bright than the Ursa Major. Since it contains Pole Star, so it is also known as the Pole star constellation. It is called "Dhurba Matsya", “Laghu Satarishi" in Nepali.

3. Orin

Orin is also called the Hunter. It has seven bright stars and several faint ones. Four bright stars mark the shoulder and legs of the hunter and three stars marks its belt. Other fainter stars complete the picture. The arrangement of stars in this constellation resemble a hunting man. This constellation is visible in the winter and is easy to locate.

4. Scorpio

This constellation contains seven bright stars. Along with other faint stars, it forms the shape of a scorpion. It is visible during the summer season. Its shape is just like W. It is seen in the northern hemisphere. The distance between of Cassiopeia and Big Dipper is nearly the same from the polar star.

Measuring distance in the Universe

The distances between heavenly bodies in space are very large. Measuring those distances in km would be mean dealing with very large numbers. Astronomers, therefore uses special units to measure the distance in space. Instead of km, they use light year to measure the distance between two heavenly bodies. A light air is the distance that light travels in one year.

1 light year = 9.5 x 1012 km

Astronomers also use another unit for measuring large distances which is called parsec. Parsec is an astronomical unit of distance which is equal to 3.26 light years. That is 1 parsec = 3.26 light years.

Comets

A comets is a collection of gas and dust which appears as a bright ball of light in the sky with a long glowing tail. Comets are also the members of our solar system. They revolve round the sun like the planet do. The period of revolution of comets round the sun is very large. The comet has bright head, probably made up of an enormous swarm of rocks of various sizes, dust and a tail, many millions kilometers long. Some comets through our solar system once, they disappear. They become visible only when they approach the sun. Some comet appear in our solar system at regular intervals. Halley Comet is one of them. It appears every 76 years since then. It was last seen in 1986.