A telescope that focuses light with a bowl of liquid mercury instead of a solid mirror has opened its eyes to the skies above India. Such telescopes have been built before, but the 4-meter-wide International Liquid Mirror Telescope is the first large one to be purpose-built for astronomy.
The $2 million instrument, built by a consortium from Belgium, Canada, and India, is less expensive than telescopes with glass mirrors. The 3.6-meter, steerable Devasthal Optical Telescope was built by the same Belgian company at the same time and cost $18 million. The director of the University of Lige says that simple things are the best. Liquid mirrors are the perfect technology for a giant telescope on the Moon that could see back to the beginning of the universe.
When a bowl of reflective liquid mercury is rotating, the combination of gravity and Centrifugal force pushes the liquid into a perfect parabolic shape, but without the expense of casting a glass mirror blank, grinding its surface into a parabola, and coating it with reflective aluminum
It was dreamed up in the 1990s. The mercury holding vessel was delivered to India in 2012 but construction of the telescope enclosure was delayed. Researchers discovered they didn't have enough mercury. They were unable to travel to India due to the COVID-19 Pandemic. The team set 50 liters of mercury and created a 3.5 millimeter thick layer. A member of the team says that they are all very happy.
Earth's rotation scans the sky from dusk to dawn and the rotating mirror will show a swath of sky almost as wide as the full Moon. The person says to turn it on and let it run. The objects appear as long streaks in the image and can be combined to create a single exposure. Exposures from many nights can be combined to get extremely sensitive images of faint objects.
Transient objects such as supernovae and quasars can be seen if the image is subtracted from the next one. In this case, the light of a distant object is magnified by the gravity of a cluster. It is possible to estimate the expansion rate of the universe thanks to the sensitivity of the object's brightness. According to a study, there could be as many as 50 lens in the sky.
Survey telescopes such as the Zwicky Transient Facility in California and the Vera C. Rubin Observatory in Chile are used to cover a lot of the sky. They are not likely to go back to the same patch every night to look for changes. There is a niche that we have to have. DOT is equipped with instruments that can quickly scrutinize any fleeting objects discovered by its next-door neighbor. The director of the research institute that runs the Devasthal Observatory says that the approach is more comprehensive and scientifically more rich.
It's an attractive location for future giant telescopes because it's less active than Earth and has no atmosphere. From the planet's rotation, the Coriolis effect warps the motion of mercury in mirrors bigger than 8 meters. Mercury is not allowed in larger liquid mirrors because of the Moon's slow rotation. It is too heavy to travel to the moon at night. More than a decade ago, liquid mirror pioneer Ermanno Borra showed that lightweight molten salts with low freezing points could be made reflective with a thin coating of silver.
The Canadian Space Agency commissioned studies of lunar liquid mirror telescopes in the 2000s, but didn't go any further. The cheap launches offered by private space companies will hopefully spur a revival. A team at the University of Texas, Austin proposed the Ultimately Large Telescope, a 100 meter liquid mirror that would stare at the same patch of sky for years on end from one of the Moon's poles. The first stars that lit up the universe were gathered by a giant. Roger Angel, a veteran mirrormaker at the University of Arizona, says there is a niche for a big mirror that goes beyond what others can do.
All Rights Reserved © 2024
