The sun is a star in the Milky-Way galaxy. The sun was formed about 5 billion years ago. The sun is a middle-aged star having average brightness. It appears bigger and brighter than the nighttime stars because it is so much closer to us. It is the nearest star to the earth; it is 300,000 times closer to us than any other star. Though the sun is the nearest star to the earth, it is 150 million kilometres away from the earth. Light takes about 8.3 minutes to reach us from the sun. The light from the next nearest star, Alpha Centuri, takes about 4.3 years to reach the earth.
Chemically he sun is a gaseous mass of hydrogen that is continuously being changed into helium at extremely high temperatures. This nuclear reaction liberates a tremendous amount of energy. A part of this energy reaches the earth is responsible for sustaining life on it.
The sun contains about 99 per cent of the mass of the solar system. The sun is 109 times wider than the earth and is 330,000 times heavier than the earth. Like the earth, the sun rotates on its axis once every 25 days. The sun is travelling in our galaxy along with the other members of the solar system at a speed of about 70,000 kilometres per hour.