India to use a liquid mirror telescope for astronomy for the first time
You all know what a telescope is, right? If you are a space enthusiast, you’re sure to have seen a telescope first-hand at your local planetarium. Or you at least know extensively about it from the internet, don’t you? For the unversed, a telescope is a monocular optical instrument used to observe distant celestial objects. But how does it work? Well, it is first steered to point towards a celestial body. Once set, it magnifies what’s visible to make them clear to the naked human eyes.
Now, imagine a telescope that does not need to be steered. Instead, it can capture a portion of the sky as a whole at any given point in time and place, on its own. How interesting is that? Well, this is what a liquid-mirror telescope does. Such telescopes existed since 1872 when Henry Skey, a New Zealand-based astronomer, constructed the first functional laboratory-made liquid-mirror telescope (LMT). Since then, liquid-mirror telescopes have come a long way. However, all the liquid-mirror telescopes built so far have been used to track satellites or deployed for military purposes, not for astronomy, until recently.
First liquid mirror telescope for astronomical purpose
In June 2022, India was allowed to use a modern-day international liquid-mirror telescope (ILMT) for astronomical research. According to several sources, ILMT will begin full-scale astronomical operations in October. guess what, this made us the first country in the world to have commissioned its use. It is also the world’s largest ILMT with its four-metre diameter.
ILMT has been set up at the Devasthal Observatory in Nainital, Uttarakhand, amidst the Himalayas at an altitude of 2450 metres. The Aryabhatta Research Institute of Observational Sciences (ARIES) oversees the project. Astronomers believe it can observe celestial bodies, from asteroids and meteorites to supernovae and space debris.
A Joint Mission, for the love of space
India is not the lone developer of ILMT. In fact, four other countries, namely Belgium, Canada, Poland and Uzbekistan, joined hands to construct the International Liquid-Mirror Telescope. It was designed and manufactured at the Advanced Mechanical and Optical Systems Corporation and the Centre Spatial de Liege in Belgium. While Canada and Belgium came together to allocate the funds (INR 30 to 40 crore), the technical operation and maintenance part has been undertaken by India.
How does a liquid mirror telescope function?
Simply put, a liquid-mirror telescope is the one having mirrors carved out of reflective liquid, such as mercury (metal having a high light-reflecting power). This liquid is poured into a parabolic-shaped container and made to rotate at a steady speed around a vertical axis. When this process is on, the mercury spreads as a thin layer floating on a layer of compressed air that is10 microns thin (thanks to gravity and centrifugal forces) until its surface assumes the shape of the container. This then acts as a liquid (read mercury) reflector and serves as the telescope's primary mirror that can both collect and focus light. However, they are so sensitive that even smoke particles can damage their part called air bearings! The four-metre-wide ILMT is also equipped with cutting-edge computational tools such as AI, machine learning and big data analytics for better astronomical research.
Solid vs. liquid
As already m, a traditional telescope needs to be controlled in a way meant to target a particular celestial object that one intends to observe. After that, the light gets reflected, in turn creating relevant images. In contrast, the liquid-mirror telescope can view any celestial object from its stationary fixed position. This means it can survey and observe all kinds of space objects at any time.
Besides, a normal telescope has a solid glass mirror (single or a pair of curved ones) that needs to be cast, grounded and polished, making it expensive to manufacture. On the other hand, as described above, a liquid-mirror telescope is composed of a mirror made from a reflective liquid such as mercury that is cheap and easily available, making the production cost-effective.
Furthermore, there's a striking difference between the operational time of the two. In the case of a normal telescope, it is usually meant to observe a particular celestial object or phenomenon for a short, fixed period. As against this, the liquid-mirror telescope can study the sky all night, for example, in the case of ILMT, every night (starting from twilight) for the next five years. To change the region of the sky you want to see through the ILMT, you have to entirely reposition it!