Telescope Mirrors

Mirrors are truly amazing devices. You can see your face in a mirror.  If you put a few mirrors in a tube, you can make telescope mirrors that will help you examine the Universe at a more advance level. But the bigger the mirror the more expensive it becomes and this equation is not proportional.  If you double the size of a mirror, you make the mirror 10 times more expensive. But studies show that you can make a 2.5 metre mirror for less than the price of a new family car - using liquid mercury!

People have always like the concept of a mirror, ever since they saw their own reflections in water some 5,000 years ago.  Beyond this the Greeks taught people how to make different types of mirrors and by 100 BC, the Romans had glass telescope mirrors with a reflective layer of silver behind the glass.

Isaac Newton was the person who really worked out how to use telescope mirrors. These days the standard amateur telescope might have a 15 cm mirror, a more serious amateur telescope might have a 40 cm mirror and the professional astronomical mirrors begin at around 1 meter across, right up to approximately 4 to 8 meters.

So how can telescope mirrors be made so inexpensively? Easy really!  The shape of a telescope mirror is not the shape of a sphere but instead a shape called a parabola. A parabola brings incoming parallel rays of light to a single point - which is exactly what is required for a sharp, crystal clear image. Now while it's fairly easy to grind a mirror to the shape of a sphere, it's complicated and expensive to grind it to a parabolic shape.
But in an act of complete coincidence when you spin a liquid in a container, the surface of that liquid takes on the shape of a parabola. This naturally means that liquid is the optimal solution for making telescope mirrors in the most inexpensive manner and one professor at the University in Quebec, has been making spinning liquid mercury mirrors for telescopes for decades.