What is the Visible Emission Line Coronagraph (VELC)?

About Visible Emission Line Coronagraph (VELC):

• It is the primary payload of the Aditya-L1 Mission-India’s first mission to observe the Sun from a vantage point 1.5 million kilometres from the Earth.
• It is an internally occulted solar coronagraphcapable of simultaneous imaging, spectroscopy, and spectro-polarimetry close to the solar limb.
• It is built by the Indian Institute of Astrophysics (IIA) at its CREST (Centre for Research and Education in Science and Technology) campus at Hosakote, Karnataka.
• The VELC consists of a coronagraph, spectrograph, polarimetry module, and detectors, aside from auxiliary optics.
• Purpose:
• It will observe the solar corona, which is the tenuous, outermost layer of the solar atmosphere. 
• VELC can image the solar corona down to 1.05 times the solar radius, which is the closest any such payload has imaged.
• It will analyze the coronal temperature, plasma velocity, density, etc.
• It will also study Coronal Mass Ejections (CMEs) and the solar wind. 

What is a Coronagraph?

• It is a specialized instrument designed to block out the light of the sun so that researchers can glimpse the burning star's hot, thin, outermost layer, called the corona. 
• The French astronomer Bernard Lyot invented the coronagraph in the 1930s.
• The sun's corona is normally visible only during solar eclipses when the moon's shadow covers the bright central layers of our parent star and allows its dimmer corona to appear.
• A coronagraph mimics this natural phenomenon with a circular mask that sits inside a telescope and selectively blocks the bulk of the sun's light.
• The specialized coronagraphs act as filters on the central star, allowing the tiny fragments of planetary light to shine through.