The first telescope was invented by an Italian mathematician Galileo Galilei. Compared with the telescopes we use today, Galileo’s telescope was a very simple instrument. It was a tube with two lenses: the convex primary lens that curved outward and the concave eyepiece lens that curved inward. He built the device after hearing about the newly invented spyglass which was an instrument used by the military to peer into enemy camps.
This first telescope that Galielo came up with used the same principle that all telescopes would eventually rely on. That principle held that the combination of the two lenses gathered more light than the human eye could collect on its own. The lenses would focus that light and form an image. Because the image was formed by the bending of light, or refraction, these telescopes came to be known as refracting telescopes, or simply, refractors.
Galileo’s first telescope magnified objects about thirty times. Because of flaws in its design such as the shape of the lens, the images tended to be blurry and distorted. However, the early telescope was good enough for Galileo to explore the sky. Using this first telescope, he could see shadows and bright spots on the moon. He could also see that the moon had mountains and valleys.
Galileo was an excellent experimentalist, and working with different lenses, he realized that the magnification was proportional to the ratio of the power of the concave (eyepiece) lens to the convex (more distant) lens. In other words, to get high magnification he needed a weak convex lens and a strong concave lens.
The problem was that the opticians only made glasses in a narrow range of strengths, and three or so was the best magnification available with off the shelf lenses. Galileo therefore learned to grind his own lenses, and by August, he had achieved about nine-fold linear magnification.
This was an enormous improvement over everything else on the market. Galileo therefore approached the Senate of Venice to demonstrate his instrument. Many senators climbed the highest bell towers in Venice to look through the glass at ships far out at sea, and were impressed by the obvious military potential of the invention.
With the invention of the first telescope, Galileo sent shockwaves throughout the world, and people began to copy his design to make it better and better. Over the years, technology would improve on Galileo’s first telescope and provide insight into the world that had never before been explored.