Introduction

The 4m ILMT is the first liquid mirror telescope entirely dedicated to astrophysical observations. The ILMT is located in the foothills of the Himalayas, at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), near Nainital in the northern state of Uttarakhand (India). Thanks to a collaboration between Belgium (ULiège), Canada (UBC) and India (ARIES), the ILMT continuously monitors the sky passing at zenith within a narrow band of 22.3 arcmin. in declination down to a limiting magnitude of approximately 22 in the Sloan g, r and i spectral bands.

The principal investigator of the project is Prof. Jean Surdej (Liège University, Belgium). Since the beginning of the ILMT project, Prof. Paul Hickson (UBC) has been acting as the project manager. The project has benefited significantly from the extensive prior research and technical developments carried out by Prof. Ermanno Borra & Prof. Paul Hickson. The astronomer in charge at ARIES is Dr Kuntal Misra.

The International Liquid Mirror Telescope (ILMT) project was motivated by the need for an inexpensive 4 metre diameter optical telescope that could be devoted entirely to astronomical surveys. Its scientific programmes include the detection and study of transients, variable objects, asteroids, comets, space debris and low surface brightness galaxies. To this end, a collaboration was formed between the Institute of Astrophysics and Geophysics (Liège University, Belgium), several Canadian universities (University of British Columbia, Laval University, University of Montreal, University of Toronto, York University, University of Victoria) and the Aryabhatta Research Institute of Observational Sciences (ARIES, India). After several years of design work and construction of the telescope in Belgium the telescope was transported in India on the ARIES Devasthal site in 2012. The telescope saw its first light on 29 April 2022. Its commissioning phase lasted from May 2022 until June 2023 (beginning of the monsoon). The ILMT was inaugurated on 21 March 2023 and has been in regular operation since October 2023. The telescope continuously observes the sky passing at the zenith using the SDSS g, r, and i filters.