Visible Emission Line Coronagraph (VELC)

Why in news?

Scientists from the Indian Institute of Astrophysics (IIA) and NASA have used the Visible Emission Line Coronagraph (VELC) aboard India’s Aditya‑L1 spacecraft to make the first spectroscopic observations of a coronal mass ejection (CME) close to the Sun. By analysing the light emitted by the ejection, the team measured the electron density, temperature, mass and speed of the CME, demonstrating the instrument’s unique ability to study the Sun’s inner corona.

Background

The VELC is the primary payload on Aditya‑L1, India’s first dedicated solar observatory launched by ISRO to the L1 Lagrange point between Earth and the Sun. Developed by the Indian Institute of Astrophysics with contributions from ISRO and other research institutions, it is an internally occulted coronagraph designed to block the bright solar disc and image the faint solar corona. The instrument performs imaging, spectroscopy and polarimetry over a range of 1.05–3 solar radii and can measure the Stokes parameters to infer the magnetic field structure.

Features and capabilities

• High‑resolution imaging: VELC provides continuous images of the inner solar corona with a fine spatial resolution. It can capture changes in the corona that take place over minutes, which is essential for understanding how CMEs originate and evolve.
• Spectroscopy and polarimetry: The instrument disperses light into its component wavelengths to measure the temperature, density and velocity of coronal plasma. Polarimetric measurements help infer the orientation and strength of magnetic fields near the Sun.
• Lagrange‑point advantage: Aditya‑L1 is stationed around the L1 point, about 1.5 million kilometres from Earth, allowing VELC to continuously view the Sun without Earth’s shadow interrupting observations.

First spectroscopic CME observation

In the recent observation, the VELC recorded a coronal mass ejection carrying about 270 million tonnes of plasma. Analysis showed that the electron density at the eruption site was roughly 1.4 × 10⁸ electrons per cubic centimetre, the total energy was about 9.4 × 10²¹ joules, and the CME travelled at around 264 km/s with a temperature near 1.8 million K. These measurements will help scientists model space‑weather events that can affect satellites, power grids and communications on Earth.

Source: Vocab24; Indian Institute of Astrophysics