The Sun is the central star of our Solar system, and has a diameter of approximately 1,392,000 kms. This massive star itself forms about 99.86% of the entire Solar System's mass, leaving less than 1% of the solar system to be made up of the planets, asteroids, comets, meteoroids, etc. Thus, from this one can get an idea about the vastness of this star.
What is the Temperature of the Sun?
In 1837, Sir John Herschel at the Cape of Good Hope, and Claude-Servais-Mathias Pouillet in France observed that the temperature of water, 1.8 cm deep would rise by 1°C/minute if the vertical rays of the Sun were to be completely absorbed. Thus, emerged the problem of atmospheric absorption.
However, this problem was solved in 1881, when astronomers compiled unknown information for solar radiation of various wavelengths from the already known data, so as to determine the intensity of each one in the absence of intervening air. This helped to measure the temperature of this star. The temperature varies at different layers and regions of the Sun.
The surface of the Sun is also called the photosphere, which is 340 miles thick and gives off Sun's energy in the form of light and heat. One can view some dark spots, also known as Sunspots that happen to be the only activity visible to us by the naked eye. In fact, most of the sunlight we see is from this photosphere only.