Definition of Sun
The sun is a typical star which is about 150 million km away from the Earth. Solar ennergy provides virtually all the heat & light which are received by our planets & it therefore sustains every living entity. The character of our own environment is strongly influenced by solar radiation which has been a major factor in determining the course of natural evolution on earth. The Sun is important to Astronomers & physicts because it enables them to investigate physical conditions, which are typical of most stars, in detail. Historically, the study of the sun led to significant advances in atomic physics, nuclear physics, magnetohydrodynamics & plasma physics. An understanding of solar processes is therefore of biological & physical interest & several several fundamental areas of scientific research are furthered by observing this local astrophysical laboratory. Satellites have enabled space scientists to probe more closely the interaction between the Sun & the earth, especially the influence of the sun on the magnetic field of the Earth.
Before describing the Sun in detail we must issue an important warning about observing the Sun: imtense solar radiation permanently damages the tissue of the human eye. The Sun must never be viewed directly with a telescope, whcih would have the effect of concentrating a massive dose of radiation on to the delicate tissue. The solar filters sold with many cheap telescopes are not an adequate safeguard because they may admit a dangerous dose of invisible ultraviolet light or may shatter unexpectedly. They should be destroyed in order to remove the temptation to use them. With a little experimentation, good images of Sun can be produced by projecting through an eyepiece on to a piece of stiff card. This arrangement is adequate for viewing sunspots or the progress of an eclipse. An eclipse may also be observed by the unaided eye by looking at the Sun through a really dark filter or looking at the reflection in a dark container of still water, but even these methods require caution.