Earth’s Galaxy: The Milky Way

⇒ We live on the outer edge of a spiral type of galaxy called the Milky Way, which is about 1,00,000 light years in diameter and is rotating slowly.

⇒ The Milky Way is a large spiral-shaped galaxy.

⇒ It spans about 1,00,000 light-years across and is about 10,000 light-years thick at the centre. vody gleA

⇒ It is called the Milky Way because it appears as a soft glowing light of billions of stars. These stars are so far that they can be seen only in constellation, not separately.

⇒ Galileo discovered that this band of light was produced by countless individual stars which a naked eye can not see. It takes about 250 million years to complete one revolution.

⇒ Andromeda is a spiral galaxy and also our closest neighbour. It appears as a fuzzy patch of light and contains millions of stars.

⇒ It is the farthest object that can be seen with the naked eye. Along with the Milky Way, it belongs to a group of galaxies known as the Local Group, which in turn is a part of Virgo Cluster of groups.

⇒ Like stars, galaxies are grouped into clusters. Some clusters contain thousands of galaxies. About 30 galaxies, along with the Milky Way and the Andromeda are grouped together in one cluster called the Local Group.

⇒ Clusters may group together into upper clusters. Super clusters are also spread randomly throughout the universe.

⇒ Nebulae are huge interstellar clouds of gas and dust that appear as faint, misty patches of light scattered all over the sky.

⇒ They appear either as bright luminous clouds or as dark patches against a brighter background.

⇒ A nebula depends for its luminosity upon the presence of stars that have either arisen from it or are contained in it.

⇒ If the stars are extremely hot, the hydrogen in the nebula is ionized and emits a certain amount of light of its own. reflection.

⇒ If a star is less hot, the nebula shines only by reflection.

⇒ If there are no suitable stars, the nebula does not shine EST and remains dark and can be detected only because it blots out the light of the stars beyond.

⇒ There are five types of nebulous objects in the sky 1. Planetary nebulae, 2. emission nebulae, 3. reflection nebulae, 4. dark nebulae and 5. supernova remnants.

Shape of the Earth: Pythagoras (572-500 B.C.), a Greek philosopher and mathematician, was among the first to suggest that the Earth was shaped like a globe.

The Earth is not flat: If the Earth were a flat disc, then the rising Sun would have been seen at all places at the same time. But this does not happen. Places in the east see the rising Sun earlier.

⇒ When a ship approaches land, its funnel or mast is seen first and then the hull. If the Earth had been flat, the whole ship would have been seen at the same time.

The Earth is a sphere: The Earth is rarely oriented in the same position during successive eclipses but it always casts a circular shadow, thus proving that the Earth is a sphere. A sphere is the only solid body that will always cast a circular shadow.

⇒ At the North Pole, the Pole Star can always be observed at 90 degrees in the sky, since the star lies in the line with the axis of the Earth.

⇒ As one travels southwards, the angle of Pole Star decreases. At the Equator the angle becomes zero degree. This observation proves that the path of travel is an arc of a circle.

⇒ The Sun, Moon and all the heavenly bodies appear to be spherical when viewed from different positions. It seems logical to conclude that the Earth is no exception.

⇒ The photographs of the Earth taken from the space prove beyond any doubt that the Earth is a sphere.

The Earth as an Oblate Spheroid : Refined measurements of the Earth have proved that the true form of the Earth resembles a sphere that has been compressed at the poles and made to bulge at the Equator. This form is known as an oblate spheroid.

⇒ The earth has all the essential elements like carbon, hydrogen, nitrogen and oxygen, which act as building block for the origin of life.

⇒ The earth is neither too hot nor too cold. It has the right temperature range for carrying out the life-sustaining chemical reactions.

⇒ The earth has a lot of water in the form of lakes, rivers and oceans for the growth and Composition of Earth (%) survival of life.

⇒ The earth has enough oxygen gas in its atmosphere for the survival of living beings through breathing.

⇒ The earth has a protective blanket of ozone layer high up in its atmosphere to save life from harmful ultraviolet radiations coming from the sun.

⇒ Biodiversity changes increase towards equator. Biodiversity is the degree of variation of life. It is a measure of variety of organisms present in different ecosystems. It is richest in the tropics.

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