ABSTRACT
This chapter provides a brief chronological development in our knowledge about the Sun as derived historically from the very limited observations of its visible (optical) disk. Many new discoveries were made after telescope was invented in 1610. Visual observations were followed by photography of eclipses. Sunspots, their prolonged disappearance during the Maunder Minimum period of 1645-1715, limb darkening, solar differential rotation, solar flares were the major discoveries from the observations of the photosphere. The next revolution came in solar physics subsequent to the birth of spectroscopy in the nineteenth century. Dark absorption lines, known as Fraunhofer lines, were discovered in the solar photospheric spectrum, and were recognised as the ‘thumb prints’ of the elements present in the solar atmosphere. Solar spectrum obtained during solar eclipse led to the discovery of Helium, and forbidden lines that signified million degree temperatures of solar corona. Presence of strong magnetic fields inferred from Zeeman splitting of spectral lines, and radial out-flows (Evershed flow) from Doppler shifts were the milestones in modern solar physics. From simple observations, combined with laws of physics, this chapter goes on to derive global properties of the Sun, such as, the effective temperature, solar mass, density, diameter, distance, elemental abundances, age and luminosity. It discusses the extended solar system, birth and evolution of the Sun, and the place of the Sun as a star in the Milky Way Galaxy.
