The sun and the solar atmosphere, known as solar corona have been studied in detail for centuries but still lot need to be understood about the sun. In the late 19th and earlier 20th century, the information gathered about the solar corona was from the brief moments available during the total solar eclipses. In the later part space observations provided a large body of information about the solar corona. We obtained systematic high resolution spectroscopic observations in [Fe x] 637.4 [Fe xi] 789.2, [Fe xiii] 1074.7, and [Fe xiv] 530.3 nm emission lines during the period of 1997-2007 with the 25-cm coronagraph at Norikura, Japan. The variation in line widths with height above the solar limb implies that one pair of lines indicate that top of coronal loops are hotter where as other pair of lines shows that loop top is cooler. To explain these results, we proposed an empirical model as all these results are difficult to explain using the existing models. With this background we planned and designed a visible emission line coronagraph (VELC). This instrument is in advance stage of fabrication and is expected to be launched in 2019-20. The challenges and required technical development for this mission are discussed.
The Sun-Spectroscopic Observations of the Coronal Emission Lines and ADITYA-1 Mission