The first telescope was fashioned by German lens-maker Hans Lippershey in 1608, though the first true astronomers were Galileo Galilei and Thomas Harriot, each of whom began stargazing in the early 1600’s. Since then, humans have been finding countless ways to get a closer look at the stars. More types of telescopes have existed than you can probably imagine, some of them now obsolete and others rare but still in use. We’ve identified 14 different telescope types that showcase the unique qualities found in telescopes across the globe.
Refractor telescopes are built with lenses that refract light and send it along a focal path within the telescope tube. An eyepiece captures the light at its focal point, creating the image you see within. Below are 4 types of refractor scopes and their common uses.
A refractor telescope gathers light at every wavelength, but not all wavelengths have the same focal length inside the telescope tube. This creates chromatic aberration, a sort of fuzziness around the outside of the object you’re viewing as the light waves scatter toward the edges. An achromatic telescope uses a special lens made by combining Flint glass and Crown glass to achieve different light dispersion, correcting these aberrations.
Like an achromatic telescope, an apochromatic telescope uses a special lens to correct chromatic aberration. The apochromatic lens differs in that it disperses three wavelengths at a time instead of two. While apochromats contain the same glass as the achromatic lens, they typically also contain liquid between the lenses for added dispersion.
Like the apochromatic and achromatic lenses, a superachromat corrects aberrations by bringing different colors into focus at the same time. The superachromat is quartic, meaning it disperses four colors simultaneously. These highly fine-tuned lenses are built with expensive fluorite glass to achieve the best type of image correction.
An inexpensive telescope produced for the 2009 International Year of Astronomy, a Galileoscope is a refractor scope built to bring astronomy to the masses. It is versatile enough to use with various eyepieces to enhance magnification, and economical enough for kids and amateur enthusiasts. Its narrow field of view and 17x magnification are meant to parallel the kind of telescope Galileo would have used, in effect harnessing the astronomy of the past to bring new interest to the field. The best part is, they come in a kit so you can build them yourself.
Invented in 1611 by Johannes Kepler, the Keplerian telescope uses convex lenses to widen the field of view from Galileo’s concave lens prototype. While Kepler’s invention meant higher magnification strength for telescopes, it also inverted the image.
A reflector telescope is built with mirrors that elongate the focal path of the light entering it. This style was invented by Sir Isaac Newton in the 1680s and became popular due to its enhanced image clarity.
Isaac Newton’s original invention from 1668, and the basis for most reflector telescopes developed since. Light enters through a parabolic or spherical primary mirror, which bounces the light back up the telescope to a secondary plane mirror, when then sends the light to the eyepiece at a 90-degree angle. Because they are optically “fast,” they tend to be much shorter than a refractor. The absence of lenses also solves the problem of chromatic aberration.
RELATED: we also reviewed Dobsonian telescopes here. (these are very close to Newtonian reflectors)
A Cassegrain reflector telescope uses a series of concave and convex mirrors to fold the light path to enhance its focal length and improve magnification. A hole in the center of the primary, parabolic mirror sends light to the eyepiece.
Instead of a glass mirror, a liquid mirror telescope uses a rotating dish of highly reflective liquid, usually mercury. The rotation causes a parabola effect in the liquid’s surface, which reflects light onto a non-liquid mirror for viewing. This method is used to create a telescope both quickly and inexpensively.
This type of telescope contains three parabolic mirrors which help correct aberrations such as spherical, astigmatism, and coma. Typically, the first mirror will correct any spherical aberrations on its own. But adding a second and third mirror eliminate the other two aberrations. Together, they widen the field of view and provide a clearer image.
The marriage of catoptric and dioptric (refractor and reflector) engineering is the catadioptric telescope. This combination is the best of both worlds, providing mirrors and lenses that better correct aberrations and provide a wider field of view. Their method of folding the light path within the telescope tube means faster optics and a shorter device.
A catadioptric telescope that uses spherical mirrors and corrector plates to prevent spherical aberration. Their focal path is long, but their field of view is narrow, perfect for observing planets or for deep-sky viewing. Most catadioptric telescopes are derivatives of the Schmidt-Cassegrain telescope, or SCT.
A telescope used for astrophotography. Containing a spherical primary mirror and Schmidt corrector, the device sends light to a focal point where it is captured by film. They have a wide field of view and are often used to track satellites, comets, and asteroids.
Infrared telescopes must be in a dry, high altitude environment in order to detect infrared space radiation without interference. These telescopes are used to gather information about our universe’s history. Because light travels for so long before it reaches Earth, it has had time to become detectable infrared radiation. This radiation dates back to the beginning of the universe, providing insights into the vast history of the cosmos.
Ultraviolet telescopes can tell us a lot about the physical components of distant planets and stars. They pull UV light apart into a spectrum so that brightness can be measured at each wavelength. This reveals the presence of elements, an object’s density, and temperature. These telescopes require precision lens coating and smoothness to be effective, and because Earth’s ozone filters out UV rays, they must be mounted to satellites above the ozone layer.
Extremely hot objects in the universe radiate X-rays, so X-ray telescopes were invented to observe the effects of huge explosions, collapsed neutron stars, and black holes. These telescopes tend to be barrel-shaped in order to harness the ricochet effect of X-rays when they strike a mirror. In order to detect this unfiltered radiation, X-ray telescopes must also be mounted on satellites.
This is a small sampling of the types of telescopes that engineers have created over the past few hundred years, and they won’t be the last. Digital technology and scientific knowledge both advances at a breathtaking pace, and new discoveries are always around the corner. Still, there is something fascinating about the technology Galileo and Newton used to make their observations and discoveries so long ago. It’s also exciting to think about where technology will take us next.
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