What is a liquid mirror?
It has been known for several centuries that the surface of a spinning liquid takes the shape of a paraboloid that could, in theory, be used as a telescope's primary mirror. One can easily verify that by adding the vectors of centripetal and gravitational accelerations, one obtains a parabolic surface. The first known mention of a liquid parabolic mirror was made by the Italian astronomer Ernesto Capocci around 1850.
The focal length f of a liquid mirror is related to Earth's gravitational field g and the angular velocity ω of the turntable by:
For large mirrors of practical interest in astronomy, optimal rotational periods are of the order of 10 seconds, with linear velocities at the edge between 5 and 20 kilometers per hour. The photograph below shows a mercury liquid mirror with a diameter of 3.7 meters that has been extensively tested in our laboratory at Laval University.
If you would like to know more about liquid mirrors, why not download
: Liquid Mirrors: A Review
by Ermanno Borra published in the Canadian Journal of Physics in 1995.
If you're interested in the history of liquid mirrors, download
Brad Gibson's paper: Liquid Mirror telescopes: History
and learn how the concept evolved to give the liquid mirror we know.
Otherwise you might find what you're looking for in our publications.