Beginner’s Guide to Astronomy – Refractor Telescopes

If you ask someone to describe or draw a telescope, nine times out of ten it will be a refractor.

The refractor telescope is quite possibly the most common or easily recognized telescope. It is a very simple design, which has been around for hundreds of years.

The history of the refractor is that it was first invented in the Netherlands in 1608, and is credited to 3 individuals; Hans Lippershey, Zacharias Janssen – spectacle-makers and Jacob Metius.

In 1609 Galileo Galilei heard about the refracting telescope and made his own design, publically announcing his invention and further developing it through extensive experimentation. Galileo’s friend Johannes Kepler further experimented with the design, introducing convex lenses at both ends, improving the operation of the telescope.

Many advances were made and the refracting telescope became the primary instrument for astronomical observations, but there was one problem; they were huge and some were many tens of feet long!

But now, after more than 400 years and — luckily — through advances in know-how and technology, the refractor has become much more powerful and compact than some of the behemoths in the early days.

Refractors or refracting telescopes employ a simple optical system comprising of a hollow tube with a large primary or “objective lens” at one end, which refracts light collected by the objective lens and bends light rays to make them converge at a focal point.

Light waves which enter at an angle converge on the focal plane. It is the combination of both which form an image that is further refracted and magnified by a secondary lens which is actually the eyepiece. Different eyepieces give different magnifications.

The larger the size of the objective or primary lens = more light gathered. So a 6 inch refractor gathers more light than a 2 inch one. This means more detail can be seen.

There are two main types of refractor telescopes: “Chromatic” – entry level and upwards with 2 lens elements and “Apochromatic” – premium, advanced and expert level telescopes with 3 or more very high quality lens elements with exotic mixes of materials.

Chromatic refractor telescopes are particularly good for observing bright objects such as the moon, planets and resolving things like double stars, but many astronomers who image deep sky and other objects use very high quality apochromatic refractors, due to their superior optics.

Refractor telescopes are very low maintenance due to being a sealed system and it is a simple case of setup and enjoy, without the fiddling lengthy setup times you may get with other telescopes.

Refractors give clean and crisp views due to the sealed nature, unlike other telescopes like Newtonians which are subject to cooling and air turbulence issues.

Due to their small size they are very portable and can also be used for terrestrial observations the same as binoculars, which are basically two refractors bolted together.

Christie’s to Auction off 1st Edition Works by Newton, Galileo


It’s too bad that they missed Black Friday, but you’ll at least be able to get a few gifts for that astronomy enthusiast friend of yours for Christmas (or even for yourself!). The auction house Christie’s will be putting on the block 160 pieces from Edward Tufte’s rare book collection December 2nd in New York City.

Among the works are original 1st edition copies of such books as Isaac Newton’s Opticks (1704), and Galileo Galilee’s Sidereus nuncius (1610) which is better known in English as The Starry Messenger. Galileo famously reported some of his early telescopic observations in this book, discovering the moons of Jupiter and craters and mountains on the Moon. There will also be a copy of RenĂ© Descartes’ Principia philosophiae (1644) and various works by other famous astronomers, philosophers and scientists.

Edward Tufte is a Professor Emeritus of Political Science, Statistics, and Computer Science at Yale University. According to his bio on their site, “His research concerns statistical evidence and scientific visualization.” Looking through the Christie’s catalog, his interests in science history and visualization are well-represented, and the collection is quite impressive.

Of course, all of these items come at a price, rare and famous as they are. Would you expect anything less from such a notable auction house? Opticks is billed to sell for $30,000 – $40,000, Principia philosophiae for $6,000 – $8,000 and Siderius nuncius – the most expensive of the entire lot – is valued at between $600,000-$800,000 (all amounts in US Dollars). Here are a few other items for sale, accompanied by their expected fetching price:

– John Snow – On the Mode of Communication of Cholera (1849) $10,000 – $15,000 This is an important book that revolutionized our understanding of disease transmission. Steven Johnson’s book Ghost Map is based on this work, and is a fascinating read.

– Euclid – Elements $400 – $600 A 1589 copy of this important mathematical work that underlies our understanding of physics and math today. Euclid was born around 300 BC, and the oldest fragment of the Elements only dates to 100 AD.

– Thomas Hobbes – Leviathan, or The Matter, Forme, & Power of a Common-Wealth(1651). $15,000 – $20,000 A very influential work in the history of political philosophy and social contract theory. You may recognize this quote from chapter 12 of the book, “…and the life of man, solitary, poor, nasty, brutish and short.”

– Christiaan Huygens – Systema Saturnium (1659) $25,000 – $35,000 This is a digest of Huygens’ observations of the Saturnian system, and contains one of the first drawings of the Orion nebula.

– Edmund Halley – A description of the passage of the shadow of the moon, over England, in the total eclipse of the sun, on the 22nd day of April 1715 in the morning. (1715) $15,000 – $20,000 An illustrated broadside of Halley’s prediction of the shadow cast by the lunar eclipse on April 22nd, 1715. There are a few other works from Halley for sale as well.

I suggest sifting through the catalog – there are a lot of detailed photos and descriptions of the books for sale, many of them rare gems from the history of philosophy and astronomy and science.

Tufte is also selling a piece of his own artwork for $50,000 – $70,000 titled, Pioneer Space Plaque: A Cosmic Prank (2010). A digital print that uses animation electronics, it is a redesign – and parody – of the original plaques that still fly aboard the Pioneer 10 and 11 probes. For a picture, visit the auction page.

Source: Scientific American, Christie’s

Who Invented the Telescope

The history of the telescope dates back to the early 1600s. Galileo Galilei is commonly credited for inventing the telescope, but this is not accurate. Galileo was the first to use a telescope for the purpose of astronomy in 1609 (400 years ago in 2009, which is currently being celebrated as the International Year of Astronomy). Hans Lipperhey, a German spectacle maker, is generally credited as the inventor of the telescope, as his patent application is dated the earliest, on the 25th of September 1608.

Lipperhey combined curved lenses to magnify objects by up to 3 times, and eventually crafted sets of binocular telescopes for the Government of the Netherlands.

There exists some confusion as to who actually came up with the idea first. Lipperhey’s patent application is the earliest on record, so this is usually used to settle the debate, although another spectacle-maker, Jacob Metius of Alkmaar, a city in the northern part of the Netherlands, filed for a patent for the same device a few weeks after Lipperhey. Another spectacle-maker, Sacharias Janssen, also claimed to have invented the telescope decades after the initial claims by Lipperhey and Metius.

Regardless of the inventor, most of the earliest versions of the telescope used a curved lens made of polished glass at the end of a tube to magnify objects to a factor of 3x. To learn more about how a telescope lens works, read our article on the telescope lens in the Guide to Space.

Galileo heard news of the telescope, and constructed his own version of it without ever seeing one. Instead of the initial 3 power magnification, he crafted a series of lenses that in combination allowed him to magnify things by 8, 20 and eventually 30 times. You can obtain a version of Galileo’s original telescope today, at the Galileoscope web site.

The lens telescope is still in use today in smaller telescopes, but many larger and more powerful telescopes use a reflective mirror and eyepiece combination that was initially invented by Isaac Newton. Called a “Newtonian” telescope after its inventor, these types of telescopes have a polished mirror at the end of a tube, which reflects the image into an eyepiece at the top of the tube. More information about Newtonian telescopes can be found in our Guide to Space article here.

Here’s a few more links on the history of the telescope:

Who Discovered Jupiter?

Jupiter is one of the 5 planets visible with the unaided eye. That means you can go out on a clear night, when Jupiter is up in the sky, and see it with your own eyes. No telescope is necessary. In fact, it’s one of the brightest objects in the sky. When Jupiter is there, it’s hard not to see it. So it’s kind of hard to wonder who discovered Jupiter, since humans would have known about it for tens of thousands of years.

Ancient astronomers didn’t have telescopes, but they knew there was something strange about the planets. They tracked the motion of the planets with incredible accuracy and believed that they were somehow associated with gods in their mythologies. Jupiter is named after the Roman god, thought to be the head of the gods; he’s the same as Zeus in Greek mythology.

Perhaps a better question might be, who discovered Jupiter the planet. In other words, when did astronomers realize that Jupiter was really a planet. That discovery happened when astronomers realized that the Earth was really just a planet as well, orbiting the Sun in the Solar System. The new model for the Solar System was developed by Nicolaus Copernicus in the 16th century. By placing the Sun at the center of the Solar System, Copernicus developed a model that better explained the motions of the planets as they moved through the sky.

This model was confirmed when Galileo pointed his first rudimentary telescope at Jupiter. What he saw was the disk of Jupiter and the 4 largest moons orbiting the planet. Since all the heavenly bodies were thought to orbit the Earth, it was thought to be impossible for objects to orbit one another.

Once astronomers knew that Jupiter was a planet, and they had better telescopes to study it, the exploration of Jupiter could really begin. Better and better images were taken of the planet, and more moons and even rings were discovered orbiting the planet.

And then in the space age, the first spacecraft were sent to explore Jupiter. The first spacecraft to arrive at Jupiter was NASA’s Pioneer 10 in 1973, followed by Pioneer 11 a few months later. These spacecraft returned images of Jupiter’s swirling cloud tops, discovered more about its composition, and revealed features of its moons.

We have written many articles about the discovery of planets in the Solar System. Here’s an article about the discovery of Uranus, and another about the discovery of Neptune.

You can also learn more about Jupiter from NASA’s Solar System Exploration Guide to Jupiter.

We have also recorded an episode of Astronomy Cast all about Jupiter. Listen to it here, Episode 56: Jupiter.