Coronal spectroscopy - Past, Present and Future

After the beginning of photography of solar corona during the eclipses in the year 1860, efforts began to carry out spectroscopic observations of solar corona. During the total solar eclipse of 1868 August 18 at Guntur, Madras state, the observation of emission line 5875Å by Janssen lead to the discovery of Helium. Next year, during the eclipse of 1869 August 7, Charles Young and William Harkness discovered green emission line around 5310Å (later measured as 5303Å). It was interpreted as due to Coronium, an unknown element. The identification of this green line in 1939 due to [Fe xiv] ion showed the corona to be hot at 10 6 K. High resolution spectroscopic observations indicated that width of emission lines to be more than expected. The excess line width was interpreted in terms of existence of non-thermal velocity. Recent spectroscopic observations have indicated a complex nature of variation of emission line parameters with height above the corona. The spectroscopy of solar corona is also performed in other wavelengths, such as UV, EUV, X-rays, visible, infrared, and radio part of the spectrum. Here, we discuss the past spectroscopic observations of solar corona, present observations with various instruments, such as Visible Emission Line Coronagraph onboard Aditya-L1, and need for the spectroscopic observations in future.