Telescopes have provided an opportunity to bring what is far away near.

As star maps, star globes, and planetariums extended understanding of the night sky for the public, telescopes of increasing capability were expanding efficiency and accuracy of data gathering in support of researchers seeking to answer questions about the composition, origin, and fate of the universe. 

In 1668, Isaac Newton introduced the reflector telescope in response to the need to eliminate color distortions, a common problem with refracting telescopes. Although the viewing area remained quite small, the use of mirrors solved the color correction problem. But size continued to be a challenge. 

A century later, British telescope maker John Dollond, advanced refractor telescope performance by successfully producing a two-lens system largely free of color distortion. Achromatic lens sets allowed production of larger refractors, dramatically extending data gathering capability. 

Once reflecting telescope mirror fabrication switched from polished metal surfaces to reflective coated glass surfaces, reflecting telescope costs dramatically declined while light gathering capability grew, greatly surpassing that of refracting telescopes. Today, virtually all research-grade telescopes are reflectors of various types and currently up to 10 meters in size. 

A refracting telescope uses a lens, as opposed to mirrors, to observe distant objects.  This particular telescope was created by John Dollond and his son Peter.  The duo had been manufacturing optical instruments since 1750.  John Dollond is also credited with patenting the achromatic lens, which allowed an individual to observe without color distortion.    

While in London in 1786, Thomas Jefferson purchased his first telescope from the Dollonds, likely one quite similar to this. 

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The Franklin Institute

Dollond Telescope

Modern astronomy was born in 1609 when Galileo Galilei used a telescope he built to observe Jupiter, Saturn, and the Moon. His systematic observations demonstrated that our moon was not a smooth object that emitted light, but one covered in craters that reflected the Sun. He shared his findings widely, transforming our concept of the cosmos. 

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Galileo Galilei’s Refracting Telescope Reproduction

We’ve watched the five visible planets glide across the sky since antiquity. It was their brightness and motion that earned them their Greek name "planan” or “wander,” and eventually "wandering star." In comparison to stars though, their commanding brightness and size led various cultures to associate the planets with alchemy, the elements, and deities.

Until Galileo turned his telescope to the planets in 1610 and described their magnified appearance in his publications, the world had been unaware of a mountainous and cratered lunar surface, that Jupiter had its own set of orbiting moons, or that Saturn also had strange and difficult to describe structures. Decades later, more advanced telescopes would clarify Saturn's mysterious structures as the now familiar rings of Saturn. 

Galileo’s observations of the moon in particular, reinforced the concept that the moon was only a reflector of the sun’s powerful brilliance and had no illumination of its own. He could clearly and easily see the terminator line as the dividing line of illumination on a curved--as in spherical--body. 

This reflecting telescope was originally placed in the rooftop observatory of The Franklin Institute, a science museum in Philadelphia. Reflecting telescopes use a series of curved mirrors collect and reflect light to a focus inside the tube. From the 1920s through the 1960s, Fecker was a leading manufacturer of professional telescopes for universities, observatories, and museums. During the 1950s, Fecker expanded its offerings to include smaller scopes for amateur use.

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Fecker Reflecting Telescope

This 10" refracting telescope was built by the Zeiss company for The Franklin Institute's Observatory in the 1930s. The telescope has a "Urania" mounting which keeps the eyepiece steady even when moving the telescope. The eyepieces provide magnifications from 35 to 468 power for both normal-view and wide-field for open cluster observation. The Observatory is covered by a 20 ton steel and glass skylight which can be rolled back quickly exposing the entire sky.

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Refracting Telescope in the Museum's Observatory

This piece of glass is a chip from the 200” primary mirror which was manufactured by Corning for the California Institute of Technology’s Hale Telescope.  The primary mirror is the principal light-gathering surface of a reflecting telescope, and they were made from shaped disks of polished reflective metal, or in later telescopes, glass.

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Glass from the making of the 200’’ Hale Telescope

Telescopes are useful tools for remote exploration of the universe because most objects in space either generate their own electromagnetic energy or reflect it. 

Each energy type carries important information about the process that created it. Analysis of the energies reveal how a star, galaxy, nebula or any other astronomical object works, even black holes! Telescopes act as collectors of those energies, bringing information from across the distant universe to Earth where researchers can read what information is carried by that energy. 

In modern astronomical research, telescopes are specifically designed to efficiently collect particular energies, usually to illuminate a specific type of process as part of some phenomenon of activity of a celestial body. Optical telescopes are designed for the efficient collection of light, radio telescopes detect radio energy, and infrared telescopes detect the heat signature of extraordinarily distant sources. 

When the telescope is combined with the most powerful tool of astronomical analysis, the spectrometer, they reveal an object’s chemical composition and temperature, and, indirectly, distance, direction of motion, speed, and mass across thousands of light years. 

Standards for Looking to the Skies with Telescopes

Next Generation Science Standards