While working to correct an extreme case of myopia (otherwise known as short-sightedness), Dutch optician Hans Lippershey stumbled upon the fact that a particular arrangement of lenses seemed to magnify distant objects.
This was the birth of the modern telescope.
Lippershey’s first telescope, or ‘dutch perspective glass’ as it was first known, came with a whopping magnification of 3x! Galileo took the design and made a better one which gave 5x magnification -- this may not sound much compared to even the most modest amateur telescope today offering at least 50x, but it was historic.
Today’s amateur astronomers routinely operate at magnifications in excess of 200x or more. The story of the invention of the telescope has been sketchy, but before Lippershey or even Galileo hit the headlines, there were other discoveries long before that were key to its invention.
Anyone who has studied a telescope will know that its main component is a lens or mirror depending on the design. Refracting telescopes use lenses to refract or bend starlight to a focus; reflecting telescopes use mirrors to reflect and focus it.
Before the telescope could be invented, glass had to be readily available. Glass, such as obsidian, occurs naturally and is produced through volcanic processes. The first evidence for a manmade process producing glass goes back to around 3000 BC where tiny glass beads were produced in northern Syria and Egypt as a by-product of metal work.
Glass-making technology started to take off in parts of Asia and Egypt around 1500 BC and soon led to production of glass vessels and beads for jewellery. Glass production continued around the world at varying paces but while this was happening other crucial discoveries were being made.
As early as the 8th Century BC ancient Romans and Egyptians had been experimenting with glass spheres that were filled with water in an attempt to increase the power of sunlight to help start fires.
Just a hundred years later, lenses were being polished from crystals and quartz -- such as the well known Nimrud lens. This beautifully ground piece of rock was found in what is now Iraq is oval in shape and had a focal length of about 11 centimeters. It is thought it may have simply been a piece of jewellery but there is growing support that it may have been used to magnify the sunlight for fire lighting.
Records are a little hazy around the first use of glass lenses but there are various mentions in historic literature. For example, a play by Aristophane in 424 BC references a 'burning-glass' that is believed to be a lens used to start fires.
Much later, around the 12th Century, 'reading stones' were used by monks and scholars to help illuminate text. These lenses were made by cutting a glass sphere in half. Experimentation showed that different sized spheres which had different curves produced more or less magnification.
By the 13th Century, glass lenses finally became commonplace in spectacles and were ground from glass specifically for that purpose.
However, it would be another 4 centuries before Lippershey made the discovery for which astronomers today will be forever grateful.