3rd December: Telescope Day

Today is Telescope Day, because Galileo invented the telescope on this date in 1621. Here are ten things you may not know about telescopes.

1. Contrary to popular belief, Galileo didn't invent the telescope. Spectacle makers Jacob Metius, Hans Lippershey and Zacharias Janssen are credited as inventors of the first telescopes, and they are said to have got the idea from watching kids playing with lenses in their shop.
2. The first telescopes were a great commercial success, mostly among merchants, who used them to spot ships belonging to their competitors and sailors, who used them to read Semaphore signals at greater distances.
3. Galileo was the first person to think of looking at the stars with one. He improved the design and built his own. He looked at Jupiter and discovered it had moons; he looked at the Moon and discovered it had craters. There was no health and safety in those days, so he also looked at the Sun and this is quite possibly why he went blind in later life.
4. Isaac Newton invented the reflecting telescope, ie one that uses mirrors, in 1668.
5. Most telescopes work by collecting electromagnetic radiation - including visible light. As well as visible light, there are telescopes that collect X-rays, gamma rays, Ultraviolet, Infrared and cosmic rays. Radio telescopes collect microwave radiation.
6. The word "telescope" comes from the Ancient Greek tele "far" and skopein "to look or see"; ie teleskopos "far-seeing". The word was coined in 1611 by the Greek mathematician Giovanni Demisiani for one of Galileo Galilei's instruments presented at a banquet at the Accademia dei Lincei.
7. The Orbiting Astronomical Observatory 2 (OAO-2, nicknamed Stargazer) was a space observatory launched on December 7, 1968 - it was the first space telescope. Putting telescopes in space means astronomers can collect types of radiation which don't pass through the Earth's atmosphere, and even optical telescopes produce better images in space because of something called "astronomical seeing" which makes images blur and flicker - the reason why stars twinkle, in a nutshell.
8. The better known Hubble Space Telescope, named after the astronomer Edwin Hubble, was launched into low Earth orbit in 1990. With a 2.4-meter (7.9 ft) mirror, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared spectra. The mirror had to be polished continuously for a year to an accuracy of 10 nanometers, about 1/10,000 the width of a human hair. However, the polishers didn't quite get it right - they were off by 2,200 nanometers, which meant the images weren't as sharp as they could be - so Hubble had to be fitted with corrective lenses to rectify the problem. An interesting fact about the Hubble Telescope is that it only takes pictures in Black and white. The colours in those stunning pictures are added using filters.
9. There was once a 40 ton telescope in Ireland built by the Earl of Rosse in 1845. It was the world’s largest for seven decades and was nicknamed the “Leviathan of Parsonstown.” However, as anyone who has been to Ireland will know, the weather isn't always that great - the telescope couldn't be used all that much because of wet and cloudy weather.
10. Not all telescopes use glass or mirrors - some use Water as a reflecting surface and there was even one made from 100,000 gallons of dry-cleaning fluid. This was made by physicist Raymond Davis Jr. to detect invisible neutrino particles from the sun. Wacky as it sounds, he won a Nobel Physics prize for it.