Telescope

A telescope is an instrument that gathers light or other radiation from distant objects and forms a magnified or brighter image of them. The first recorded telescope was a lens-based device announced by a Dutch spectacle maker in 1608, and Galileo’s improved versions in 1609 and 1610 opened the era of telescopic astronomy.

History of the telescope

Historians are not absolutely sure who invented the telescope. The earliest evidence is from 1608, when the Dutch spectacle maker Hans Lipperhey announced a new lens-based instrument that made distant objects appear much closer. It was the first scientific instrument to extend one of the human senses.

On 2 October 1608 Lipperhey applied for a patent, which produced the first written record of a telescope. The application failed. A few weeks later another inventor, Jacob Metius, filed a similar request, and the Dutch authorities learned that many other lens makers, including Zacharias Jensen, claimed to have invented it too.

News of the device spread by about November 1608, and other makers built instruments early in 1609. Thomas Harriot in England was using a telescope of about six-power by the summer of 1609, and on 26 July 1609 he made the first known drawing of the Moon seen through one.

Harriot’s drawings were more like maps than Galileo’s, using light and shade to mark out regions of the Moon much as a map of Earth marks land and water.

Galileo heard about Lipperhey’s device and made his own. His instruments reached nine-power, and he used them for his first observations of the Moon in November 1609. His book Sidereus Nuncius, published in March 1610, announced his findings and showed that the telescope had arrived as an astronomical tool.

Who invented the telescope?

No one can be named with certainty. Lipperhey was the first to apply for a patent, but Metius and Jensen made competing claims, and officials could not decide among the claimants. Spectacle makers of the period were experimenting with combinations of lenses, so several of them may have found the effect at about the same time.

The evidence cannot be checked against surviving objects. No telescopes made by Lipperhey, Jensen, Metius or any of the other early builders survive. The oldest existing instruments are two by Galileo, which are now essentially empty tubes because their lenses broke long ago, and they are on display at the Museo Galileo in Florence.

How a telescope works

A refracting telescope uses two lenses. The large front lens, called the objective, gathers light and bends it to a focus, and the eyepiece magnifies the image formed there. Because the objective collects more light than a human pupil, faint objects become visible.

The lens arrangement decides what the viewer sees. A convex objective with a concave eyepiece gives a magnified, upright image, which is the arrangement Galileo used and Lipperhey probably used. Two convex lenses give an inverted image. Lipperhey’s device may have magnified about three times, which was enough to set other instrument makers to work.

Magnification is only part of the story. A telescope’s light-gathering ability depends on the size of its main lens or mirror, and its sharpness depends on that size together with the wavelength of the radiation it collects.

Types of telescopes

Refracting telescopes use lenses. Reflecting telescopes use a curved mirror as the main light collector, and most large research telescopes are reflectors because a mirror can be supported from behind and built much larger than a lens.

Other designs collect different kinds of radiation. Radio telescopes use large dishes to gather radio waves, and space telescopes work above the atmosphere, which blurs and absorbs some light. Binoculars, spotting scopes and the handheld spyglass are everyday forms, and the Royal Museums Greenwich notes that most telescopes have been made for ordinary use on land and at sea.

Impact of the telescope

Galileo’s observations included four moons circling Jupiter and the rough, Earth-like terrain of the Moon. These findings helped weaken the older view that all heavenly bodies were perfect and that everything revolved around Earth. Observatories such as the Royal Observatory at Greenwich continued the work in the following centuries.

Telescopes were popular with people who simply wanted a closer look at the Moon than had ever been possible before.

The telescope also entered public life. Sir William Lower, after looking at the Moon through his own telescope, wrote to Harriot that it looked like a tart his cook had made the week before. Later centuries used the telescope as a symbol in satire aimed at science, the military and politics.

In recent decades telescopes have revealed thousands of exoplanets and have been used to study the surroundings of a black hole. Many of those discoveries depend on the same principle of collecting more light than the eye can.

Uses of the telescope today

Professional observatories on mountaintops and satellites in orbit study stars, galaxies and planets, while amateur astronomers observe the Moon and planets from backyards. On land and at sea, telescopes of smaller size serve in navigation, surveying and bird-watching.

Telescopes also have a close relative in the microscope, which uses a similar pair of lenses to bring tiny objects into view. Both instruments came from the craft of spectacle making.

FAQs about the telescope

Did Galileo invent the telescope? No. He built his own after hearing of the Dutch device, and he made it far more powerful, then used it to study the sky.

How strong was Galileo’s telescope? His instruments reached about nine-power, which means objects appeared nine times closer.

Who first drew the Moon through a telescope? Thomas Harriot did so on 26 July 1609, several months before Galileo’s Moon observations.

Where can original Galileo telescopes be seen? Two survive at the Museo Galileo in Florence, though their lenses are broken.

Editorially reviewed by Specialty Digest Editorial TeamLast reviewed November 4, 2026Researched and drafted with AI assistanceReport an issue