Telescope: A brief history, overview, and modern research implications

The nightly sky has fascinated early humans and modern research scientists alike. Many wonder what is out there and look to the sky for answers to questions like: are we alone? Due to the vast scale of the universe, it is not possible for us to participate in interstellar travel to seek those answers. Instead, we use powerful optics to observe and study celestial objects. One such device that has been used since early 1600s for observational purposes is called a Telescope. In the early 17th century, Galileo Galilei, an Italian Polymath, invented a telescope to study various celestial objects.

During Galiliei’s time, many astronomers and religious leaders believed that the universe was Geocentric (belief that Earth was at the center of the universe and every celestial object revolved around it). In order to refute this claim and prove that we live in a Heliocentric universe, Galileo invented a telescope to record and study the positions of the planets (and their moons) and the sun relative to Earth. Due to Galileo’s contribution to observational astronomy, today, he is referred to as “The father of observational astronomy”.

An artist’s depiction of Galileo Galilei cataloging celestial objects by using his refractive telescope.

Refracting Telescopes

One of the two types of telescopes is called a refracting telescopes. Just like the name suggests, this telescope is made entirely of refractor lenses. In fact, this telescope was the one that Galileo Galilei used. In contrast to Reflector telescopes, refractors use lenses on the tip and the end, making them much larger. Without diving too deep into optics, the telescope focuses the light by using a combination of concave lenses to produce a sharper and brighter image. One can use the Lens Maker’s equation to mathematically represent the dynamics of a refractor telescope. In regards to the cost, refracting telescopes are one of the most affordable ones. In addition, some of the ground based observatories, such as Lowell Observatory, Lick Observatory, Paris Observatory, and Yerkes Observatory, use refractor telescopes to perform academic research.

Clark Telescope located at Lowell Observatory in Arizona. This telescope is a refractor because it uses lens instead of mirrors to focus and magnify images.

Reflecting Telescopes

The type of telescope that is most widely used in Astronomy research is the Reflector Telescope. These telescopes consist of big mirrors that make them appear bulkier. In contrast to refractors, reflectors do not use lens to magnify the image. Instead, they use large mirrors to gather photons and then focus the light to magnify the image. In the late 17th century, Isaac Newton invented reflectors as an alternative to the refractors. This was done because the design of refractors made them severely suffer from chromatic aberration.

Formally speaking, chromatic aberration is an optical disturbance resulting from dispersion; a failure in lens’ ability to focus all colors to the same convergence point. In a refractor telescope, chromatic aberration takes place because of the difference in the index of refraction for different wavelengths of light. Therefore, chromatic aberration causes the image to appear blurry. Reflectors also suffer with other types of chromatic aberration, however, its broad design minimizes the impacts of it.

An example that shows the effects of chromatic aberration. As evident by this image, chromatic aberration causes the house to appear out of focus. Similarly, such phenomenon causes scientists to obtain irregular data from observing celestial objects.

Radio Telescope