GALAXIES – MILKY WAY – DARK MATTERS

WHAT IS THE MILKY WAY????

The Milky Way is the white band seen in the sky at night that has puzzled people for centuries. Today, we know that it shines because of the light of millions of stars: The Milky Way is a galaxy. There are many other galaxies in space – and many of them have very fanciful names, such as ‘The Mice’, ’Cigar Galaxy’, or ‘ Antenna Galaxy’. Although we now know about the Milky Way, there are still many mysteries and unanswered questions that baffle the astronomers, for example, the existence of ‘dark matter’.

WHAT IS GALAXY????

A galaxy is a collection of stars as well as dust and gas clouds. Although all these are several light years away, they are bound together by the force of gravitational attraction. A galaxy is a kind of a ‘star system’. Our home galaxy, the Milky Way, has a diameter of about 120,000 light years. It contains several hundred billion stars, and there are billions of such galaxies. They often occur in groups, called galaxy clusters. The cluster to which the Milky Way belongs is called the ‘Local Group’.

WHAT DO GALAXIES LOOK LIKE????

In most of the galaxies, the stars are not uniformly distributed, but instead are arranged in certain patterns. The most frequent ones are spiral galaxies. The centre of such galaxies is thick with several old, red shining stars. A flat disc stretches all around this centre in which the individual arms of the spiral are present. It has a thickness of just about 100 light years, which is very thin as compared to the size of a galaxy. The spiral arms contain a lot of young bright blue stars. If a spiral galaxy has only two arms, it is called barred spiral galaxy. Other types of galaxies are the egg-shaped ‘elliptical galaxies’ and the ‘irregular’ galaxies, which are completely disordered.

WHAT IS DARK ‘MATTER’????

Physicists calculate the total mass available in the universe by different methods. The first method is to measure the movement of the galaxies, which arises as a result of the force of attraction between them. Since this, in turn, depends on the mass of the galaxies, the researchers can determine the mass of the galaxies from their movements. The second method is to measure the luminosity of the stars, and from this determine the mass of the objects in the universe. Both the methods give different results and the missing mass is known as the ‘dark matter’. There is at least five times as much dark matter as the ‘visible’ matter and no one knows what it is…

DID YOU KNOW THAT?????

• THE BARRED SPIRAL GALAXY CALLED 'NGC 1365' MOVES AT A SPEED OF 1600 km/sec..
• THE AGE OF THE OLDEST STAR IN THE MILKY WAY IS ABOUT 13.2 Billion years..
• EARLIER THE CHINESE BELIEVED THAT THE MILKY WAY WAS A HEAVENLY RIVER WITH THOUSANDS OF FISH....THE SIBERIANS BELIEVE THAT THE SKY IS DIVIDED INTO TWO PARTS, HELD TOGETHER BY THE LIGHT BAND.

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