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The Sun and Nuclear Fusion The Sun is the greatest source of energy on the Earth. We would not have been alive if there is no Sun around us, to give us warmth. The Earth would have been very cold frozen place.

It’s the sunlight that makes it fit for organism, by giving warmth. The most basic source of food on Earth- plants make their food in the presence of sunlight. It powers the flow of find and water cycles on the Earth’s surface and sustains all life.

Mass of the Sun is about 1029 tonnes. It has been estimated that the sun has been burning for the last seven to eight billion years. The Sun contains in its core hydrogen nuclei moving at very great speeds. Whenever these nuclei fuse to form a nucleus of a heavier element a large amount of energy is liberated. It is this energy that we receive when the Earth faces the Sun. What Sunlight is Composed of ?

The sunlight is composed of lights of wavelengths ranging from ultra-violet and the visible to the hot light of infrared. The Sun emits lights of different wavelengths. Each wavelength gives us different sensation of colour. If sunlight is allowed to pass through a prism each of these wavelengths is refracted by a different amount. The result is a beautiful band of the colours of the rainbow. Violet has the shortest wavelength (0.4 microns) and red has the longest (0.7 microns). The wavelength of green light (0.53 microns) is midway between that of violet and red. In fact, Plants which prepare their food by photosynthesis mainly absorb the violet and red lights. The remaining wavelengths of light are just reflected back.

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Light whose wavelength is shorter than that of violet is called ultra-violet light. Light whose wavelength is longer than that of red light is called infra-red light. One-third of the light from the sun is infra-red. Infra-red can heat up an object in its path. The heat we feel in sunlight is due to the presence of infrared wavelengths in it. Infra-red light from the Sun heats up the land and the water on the surface of the Earth. Not all energy from the Sun reaches the surface of the Earth. Some of the light energy is reflected back in to space,

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some is absorbed by the water vapour, ozone, dust and carbon dioxide present in the atmosphere. In fact only, 47% of the energy strikes the earth’s atmosphere reaches the earth’s surface and is absorbed. What is the Source of Sun’s Energy – the Nucleus

The atom consists of a positively charge heavy nucleus and negatively charge electrons revolving around the nucleus. The atoms of an element can have different number of neutrons in their nucleus, even if they had the same number of protons in their nucleus. For example – the Uranium atom has 92 protons in the nucleus and 92 electrons revolving around it. However, not all uranium atoms have the same number of neutrons in their nucleus. Some uranium atoms have 146 neutrons while others have 143 neutrons. These two forms of uranium are called the isotopes of uranium. The number of protons and neutrons is called the Mass Number of the atom. The uranium atom with 146 neutrons is designated as U-238(238=92+146) while the uranium atom with 143 neutrons is designated as U-235.

When two particles like two fast moving protons inside the nucleus of an atom collide with one another, the colliding proton changes into a neutron and two new particles are produced. One of these is a positively charged particle of the same mass as an electron and is called positron. The other is a massless neutral particle called neutrino. Also, a lot of energy in the form of different wavelengths is released. These type of nuclear reactions occur in the interior of the sun which liberates so much energy. Nuclei of deuterium which is the heavier isotope of hydrogen, collide in the sun’s interior to produce helium.

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The energy liberated in this reaction fires the sun, which in turn emits light of different wavelengths. The reaction in which hydrogen in the sun is converted into helium accompanied with release of energy is called a Fusion reaction. For fusion to occur, the nuclei have to collide at very high speeds. Such speeds are only possible when the temperature is very high. One gram of hydrogen in the sun releases about 62 x 109 Joule of Energy.