The sun is the centre of our solar system. It is a blazing ball of gas which is the source of heat and light. Its great mass creates strong gravity to hold the nine planets in its orbits. The Sun contains more than 98% of all the matters in the Solar System.
Our Sun is an average star of yellow-white color, which indicates it is of medium age and temperature.
The photosphere is the bright visible surface of the Sun. It is a shell of hot gas several hundred kilometers thick. Above the photosphere is a thick layer of cooler gas several thousand kilometers thick. When light passes through this layer, an absorption spectrum of the Sun is formed.
Sunspots occur in elaborate groups. Some are large enough to be visible to the naked eye. Sunspots are dark in appearance compared to the bright solar disk. The sunspot is divided into two regions. The dark inner region is known as the umbra while the light outer region is called the penumbra. The number of sunspots visible changes through time. A spot may be visible for several days or weeks before it is dissolved.
The Chromosphere is about 1500 km thick. It reveals a reddish glow around the rim of the Moon during a solar eclipse. The spectrum we see is referred to as the flash spectrum. The chromosphere is best studied during a solar eclipse but it can also be studied by the aid of an instrument called coronagraph which creates an artificial eclipse.
The corona, meaning crown in Latin, is above the chromosphere. Its total brightness adds up the brightness of a full moon, yet its temperature is incredibly high. The corona changes month to month. Part of the corona is the Sun’s scattered light, another part are few bright emission lines which elements do not occur naturally on Earth. The hypothetical element is known as “coronium”.
The Solar Wind
The solar wind is the flow of protons, electrons and helium nuclei. It is the outer most extension of the sun’s atmosphere. The particles of the solar wind travels along open magnetic field lines through coronal holes but not from all parts of the Sun.