National Large Solar Telescope

NLST serve as a crucial ground-based counterpart to India's space-based solar mission, Aditya-L1, allowing for multi-wavelength, multi-perspective observations of the Sun.

In 2010, the initial proposal for the Merak NLST was made, but Ministry of Defence granted the security clearance only around 2016, and the telescope was installed at Merak in 2018 to study the solar chromosphere. The 2026 Indian budget also proposed multiple upgrades to NLST at a cost of about to be realised by 2030 for it to serve as a complement to the Aditya-L1 spacecraft.

NLST is an on-axis alt-azimuth Gregorian multi-purpose 2-meter-aperture open telescope with the provision of carrying out night time stellar observations using a spectrograph. It aims to resolve features on the Sun of the size of about 0.1 arcsec. The focal plane instruments include a high-resolution polarimeteric package to measure polarization with an accuracy of 0.01 per cent, a high-spectral-resolution spectrograph to obtain spectra in 5 widely separated absorption lines simultaneously, and high-spatial-resolution narrow-band imagers in various lines. The NLST project is a cornerstone of India's long-term strategy in solar physics. Its location in a longitudinal gap between major solar observatories in Europe and Japan is important for providing continuous observation of the Sun. The NLST complements the space-based missions like the Aditya-L1 and ground-based facilities, providing critical data for understanding the Sun's magnetic field and its influence on space weather. Project also includes the construction of the main dome, control rooms, housing for scientists and support staff, power generation facilities, and possibly a satellite communication link for data transfer. In November 2023, and also during the May 2024 solar storms, the relatively rarer Stable Auroral Red (SAR) arcs caused by the solar wind were observed in Merak.