Telescopes: From seas to space

Created 400 years ago, it's been used to explore the high seas – and the heavens. As a new exhibition opens celebrating the telescope, Steve Connor charts the story of the invention that brought space closer to Earth

No one really knows who invented the telescope four centuries ago, but whoever it was who placed a couple of polished glass lenses at each end of a tube, it didn't take long for the idea to catch on. An immediate benefit came from its maritime use on the high seas, but its most deeply philosophical role emerged when people turned the optical instrument towards the night sky. It was then they could view in impressive detail the mysterious celestial objects that had fascinated the human imagination since the dawn of time.

The name of Galileo Galilei is justifiably linked with the early development of the telescope, but for all his great insights into the instrument it is clear that he was not the first person to come up with the idea. That seems to have taken place further north, probably in Holland, where there was a fertile community of talented spectacle makers such as Hans Lippershey and Zacharias Janssen, both of whom worked in the town of Middelburg in the early years of the 17th century.

One of these early "Dutch trunke" telescopes made its way over to England and on the night of 26 July 1609 was carefully positioned by an English scholar called Thomas Harriot to point at the Moon. We know this because Harriot, a skilled land surveyor, made a sketch of what he saw and helpfully put a date on it – four months before Galileo made his own Moon drawings with the aid of a telescope.

Harriot's lunar drawing, the first to be dated, was a rough and ready affair. This was partly because of the instrument's poor magnification – it probably magnified things by no more than six times – and the fact that it had a narrow field of view, meaning that Harriot could only see a small portion of the Moon at any one time. He was nevertheless able to draw a rough outline of the "lunar terminator" – the line marking the division between night and day on the Moon as seen from the Earth – as well as a handful of features such as the dark areas of the various lunar "seas", such as Mare Crisium, Mare Tranquillitatis and Mare Fecunditatis.

His later drawings using a more powerful telescope he had built to his own specifications were far more impressive. One of them, which is to go on display later this month at the Science Museum in London, is a beautifully preserved map of the entire view of the full Moon, showing with remarkable accuracy the positions of the major lunar craters and the "shorelines" of the lunar seas.

Harriot, whose patrons included Walter Raleigh and Henry Percy, the 9th Earl of Northumberland, went on to make other important observations. He viewed the moons of Jupiter, documenting the movements of all four satellites over a period of several months, and monitored the appearance of dark spots on the Sun.

Unlike Galileo, Harriot never published his sketches or made much of his telescopic observations. Historians believe that, as a well-maintained philosopher to great and wealthy patrons, he was rich enough not to care about letting others know of his triumphs, which explains why he is hardly known today.

"Thomas Harriot is an unsung hero of science," says Doctor Allan Chapman, an astronomy historian at Oxford University. "His drawings mark the beginning of the era of modern astronomy we now live in, where telescopes large and small give us extraordinary information about the universe we inhabit."

But it was Galileo who really made the telescope famous as an instrument of celestial insight. Towards the end of 1609 and the start of 1610 he wrote and sketched his famous Sidereus Nuncius, a short treatise on his first observations through a telescope, which had of course to be approved by the Holy Inquisition prior to publication.

There is little doubt that Galileo took astonishing risks in writing this epic work. After receiving approval from the Inquisition in February 1610 he continued to add further observations that the Inquisitors could not have possibly seen or approved. He observed the movement of Jupiter and its moons across a background sky, a finding that could have easily risked the Inquisition's wrath on the grounds that it could have been used to question the cosmic centrality of the Earth.

After Galileo saw his first Dutch-made telescope he immediately set about improving on its design by refining the lenses, fitting a concave lens at one end of a lead tube and a convex lens at the other, and generally making the instruments better. His first telescope magnified three diameters, his next magnified by eight and he ended up with an instrument with a magnification of 33 diameters.

Galileo monitored the phases of Venus, observed the hills and valleys of the Moon, predicted the motions of the Jovian moons, proved the rotation of the Sun on its axis and even drew little "ears" on Saturn, the first description of its ring system. His instrument was the first to be called a "telescope", a name dreamed up by poet and theologian Giovanni Demisiani from the Greek words meaning "far-seeing".

Bigger and better telescopes soon followed in the later decades of the 17th century, with Europe's brightest minds fixated on the idea of gaining clearer and better images of the stars and planets. Johannes Kepler described a telescope with a convex objective and eyepiece lens, while in 1688 Isaac Newton introduced the first practical "reflector" telescope using a flat diagonal mirror to reflect light into the eyepiece mounted on the side of the instrument. Reflector telescopes improved further in 1672 with Laurent Cassegrain's radical invention using a small convex secondary mirror to reflect light through a central hole in the main mirror.

The history of telescope design has been based on gathering more and more light to make bigger, clearer images. This has led to wider apertures and lenses. Galileo's telescope had lenses about 4cm (1.5ins) wide, whereas the European Extremely Large Telescope (E-ELT) planned for 2018 will have a mirror diameter of 42 metres (138ft). The E-ELT will also, like all modern optical instruments, be built on top of a mountain – possibly in Chile or Argentina – to take advantage of the low humidity and atmospheric clarity that comes with high altitude.

But the clearest of all views comes from having telescopes in space, as the astounding images from the relatively small Hubble space telescope have demonstrated – studying the stars through the murky atmosphere of Earth is like bird watching from the bottom of a lake.

And of course telescopes are not just about viewing objects in the visible region of the electromagnetic spectrum. Optical telescopes are just a small part of the telescopic menagerie, many of which look very different from the traditional designs based on lenses and mirrors for bending and reflecting light. "Most people think of telescopes as things that you look through. That's far from the case," says Alison Boyle, the curator of the new Cosmos and Culture exhibition at the Science Museum, which opens on 23 July to mark the 400th anniversary of the telescope.

In addition to the light waves visible to the human eye, there are electromagnetic emissions from cosmic sources in the invisible ultraviolet and infrared regions of the spectrum, as well as X-rays and gamma rays. They all need different kinds of instruments to gather and collect information that could provide insights into some of the biggest questions of science – what happened at the dawn of creation, how are stars and galaxies formed, and will it all come to an end at some point in the distant future?

The Science Museum's exhibition attempts to tell a story that actually goes back many centuries before the telescope, when people first attempted to make sense of the unfathomable vastness of the night sky. From Harriot's exquisite maps of the Moon, to the gold-plated concentric mirrors of the JET-X space telescope, which failed to fly on its scheduled launch, the exhibition crystallises the human need to see further and clearer into the solar system and beyond. As Boyle says, we have enjoyed an endless fascination with astronomy by looking through the telescope. "It has shaped our world and changed our perception of our place in that world today."

The biggest of all prizes for the next generation of telescopes – ones with names such as Darwin and James Webb – will be to discover the first truly Earth-like planet orbiting a distant star. By monitoring the spectrographic signature in the atmosphere of such an "extrasolar" planet it may even be possible to determine whether it harbours life. If so, it could be a telescope that answers one of the deepest questions of all: are we alone?



Cosmos and Culture opens at the Science Museum on 23 July www.sciencemuseum.org.uk

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