What is a galaxy?

A galaxy is a massive group of hundreds of millions of stars, all held together by gravity, orbiting around a common center.
The milky way is the galaxy in which our Sun, Earth, and planets exist. All stars visible to the naked eye from the earth also belong to our galaxy, the Milky way. Our sun is just a star in the Milky way.
There are billions of galaxies in the Universe. Some galaxies are small having only a million stars, while some others could have as many as 500 billion stars, or even more.

Why is the Milky way special to us?



Why is the Milky way special to us?
The Milky way is the galaxy in which our Sun, Earth, and planets exist. The Milky Way is shaped like a huge whirlpool or spiral that rotates once every 200 million years. It is made up at least 100 billion stars, as well as dust and gas. It is so big that light takes 1,00,000 years to cross from one side to the other!
Scientists think that the center of the galaxy contains a super massive black hole that swallows anything passing too close. The Sun and its planets, including our Earth, lie in the quiet part of the Milky Way, about half way out from the center.

What is a solar system?

The solar system consists of the Sun, and everything that revolves round it. The Sun, eight planets including our Earth, on which we are living, their moons or satellites, asteroids or minor planets, and millions of comets and meteoroids make up the solar system. The Sun is the giant of the solar system. The mass of the Sun is much more than the masses of all the planets put together. Therefore, it occupies the centre, and is said to be the parent of the solar system. The word 'solar' means 'related to the Sun'. There may be many solar systems in the Universe.

How are galaxies born?

Scientists believe that clumps of gas joined together to form young galaxies called protogalaxies. These protogalaxies developed in different ways. Some had huge clumps of gas at the centre, which formed massive explosions. Many massive explosions forced the left over gas out of the galaxy. So, only the stars formed from the gas remained. Protogalaxies formed in this manner become elliptical galaxies.
Sometimes, a protogalaxy will contain only small clumps of gas. Since its centre will be smaller, there will be fewer massive explosions. Most of the gas is retained along with the stars that have formed, and the galaxy becomes a spiral galaxy.
Irregular galaxies are probably protogalaxies in which explosions are still going on.

Which is the oldest living tree?

Bristlecone pine trees dot the rocky landscape of the White Mountains in California. There must be something special about these mountains, for the two oldest trees in the world have been found there.
The oldest living tree till 2013, was 4845 years old! It was a bristlecone pine, which was lovingly named Methuselah. The exact location of this tree was kept a secret, for its own protection.
Then researchers found an even older tree in the same mountains. It is also a bristlecone pine, and it is believed to be 5062 years old ! In Sicily, the Tree of O ne Hundred Horses is an enormous chestnut near the Mount Etna volcano. It is thought to be about 4,000 years old. Its unusual name comes from an old legend where 100 drenched knights and their wet steeds sought refuge from a thunderstorm beneath the tree's protective branches.

What is unique about the creosote bush?

The creosote bush, also known as greasewood, is found in the warm deserts of the world. In spring and summer, these plants produce yellow flowers. But what makes the creosote bush truly unique, is its leaves. The leaves are small, and are coated with natural oils and wax to conserve water through slower evaporation. During dry periods, creosote leaves fold in half to cut their exposure to the sun. If there is a severe drought, the creosote bush sheds its leaves entirely, and remains somewhat dormant until the rains arrive. These leaves have a distinctive pungent smell that grows stronger as soon as the summer rains start. Creosote bushes produce a large number of seeds at each flowering. It takes decades for creosote bushes to grow. Even a thirty centimetre high plant is probably at least ten years old.

Why is the Narmada an important peninsular river?

The Narmada rises from Amarkantak, in the Maikal ranges of Madhya Pradesh. It runs for 1312 km, and is the third longest river which has a course that is entirely within India. The river flows from east to west, across the Indian peninsula, into the Arabian Sea. It merges into the ocean at the point called 'Bharonch'. The Narmada flows through the states of Madhya Pradesh and Maharashtra, as well as along the border of Maharashtra, and Gujarat. As a result, millions of people, including the tribal population such as Gonds, Bhils, Santhals and Kurkus are heavily dependent on its water. The Narmada basin has numerous dams. They provide water for irrigation and hydroelectric power to both rural and urban areas .