The sun is a star. It is the star round which the earth and other planets revolve. In a way, we can say that sun is the head of solar family or solar system. Compared with the millions of other stars, the sun is a medium sized star and of average brightness. The sun appears to be larger and brighter because it is much more nearer to the earth than any other star. Thus, the star nearest to the earth is the sun. Though sun is the nearest star to the earth, even then it is at a distance of 150 x 106kilometres from the earth and light, travelling at a great speed of 300,000 kilometres per second, takes about 8 minutes to reach us from the sun.The sun is not a solid body. It consists mostly of hydrogen gas. In the centre of the sun, hydrogen atoms are continuously combining to produce atoms of helium. Each time an atom of helium is formed, tremendous amount of energy is released in the form of heat and light. It is this energy which makes the sun shine. The planets and other objects in the sky reflect a part of the sunlight falling on them due to which they become visible to us.

Even our earth reflects a part of the sunlight falling on it. So, if the earth is seen from a spaceship or moon, the earth will also appear as a bright object in space, just like other planets. The planets travel with the sun through millions of stars in our galaxy at a speed of about 70,000 kilometres per hour. The sun has nine major planets revolving round it.

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The Sun is the star at the center of the Solar System. It is almost spherical and consists of hot plasma interwoven with magnetic fields. It has a diameter of about 1,392,684 km (865,374 mi),[5] around 109 times that of Earth, and its mass (1.989×1030 kilograms, approximately 330,000 times the mass of Earth (M)) accounts for about 99.86% of the total mass of the Solar System.[14] Chemically, about three quarters of the Sun's mass consists of hydrogen, whereas the rest is mostly helium. The remaining 1.69% (equal to 5,600 M⊕) consists of heavier elements, including oxygencarbonneon and iron, among others.

The Sun formed about 4.567 billion years ago from the gravitational collapse of a region within a large molecular cloud. Most of the matter gathered in the center, whereas the rest flattened into an orbiting disk that would become the Solar System. The central mass became increasingly hot and dense, eventually initiating thermonuclear fusion in its core. It is thought that almost all stars form by this process. The Sun is a G-type main-sequence star (G2V) based on spectral class and it is informally designated as a yellow dwarf because its visible radiation is most intense in the yellow-green portion of the spectrum. The Sun's color is white, with a CIE near (0.3, 0.3), when viewed from space or when high in the sky; when low in the sky, atmospheric scatteringrenders the Sun yellow, red, orange, or magenta. Despite its typical whiteness, most people mentally picture the Sun as yellow; the reasons for this are the subject of debate. In the spectral class label, G2 indicates its surface temperature, of approximately 5778 K (5505 °C, 9941 °F), and V indicates that the Sun, like most stars, is a main-sequence star, and thus generates its energy by nuclear fusion of hydrogen nuclei into helium. In its core, the Sun fuses about 620 million metric tons of hydrogen each second.[18][19]