How Do Telescopes Work?

Telescopes are like our eyes in space. They help us observe planets, stars, and all sorts of space phenomena that cannot be seen with the naked eye. They are vital in helping understand space and the universe, and drive technological innovation in space engineering. In this article, we will explore the fundamental types of telescopes and how they help us closely examine cosmic objects that are incredibly far away.

Types of Telescopes

Telescopes, fundamentally, use a mirror or lens to gather and focus light from cosmic objects. There are two types of telescopes: refracting telescopes and reflecting telescopes. Refracting telescopes use lenses to collect light via refraction, while reflecting telescopes do this with mirrors and reflection.

Most early and backyard telescopes are refracting telescopes, which are relatively small. Because large lenses are often too heavy, they are not ideal for sending to space. Instead, space telescopes such as the James Webb Space Telescope are reflecting telescopes, which use mirrors made lighter and thinner than lenses (NASA, 2024).

Refracting Telescopes

Refracting telescopes use lenses to collect and focus light, forming an image. Light from the faraway cosmic object first passes through the objective lens, responsible for gathering the light from the image. The light then passes through the eyepiece lens, which allows the viewer to see an enlarged image of the object (Kellermann & Klock, 2025).

(Britannica)

Reflecting Telescopes

Reflecting telescopes, instead of using lenses, use mirrors to direct light to a focus. To achieve this, they contain a primary mirror which is usually concave in shape. They can also collect light not visible to the naked eye, such as infrared and ultraviolet rays. 

The primary mirror is usually made of glass, and coated with a very thin material such as aluminum. They are designed to have a very low coefficient of expansion, meaning they will expand very little when exposed to high heat. This ensures that the mirror is still able to reflect light properly without distorting the image due to changes in its surface (Kellermann & Klock, 2025).

(NASA)

Conclusion

With the advancement in space research and technology, dozens of telescope kinds have emerged, such as radio telescopes which use large metal dishes instead of mirrors (Gregersen, n.d.). However, they still operate under the same principle of collecting and focusing light. Since Galileo’s first application of telescopes to observing the moon and planets, these tools have always been essential in furthering our understanding of space.

Reference List

Gregersen, E. (n.d.). Telescopes: Seeing Stars. [online] Encyclopedia Britannica. Available at: https://www.britannica.com/story/telescopes-seeing-stars [Accessed 1 Jun. 2025].

Kellermann, K. and Klock, B.L. (2020). Telescope | History, Types, & Facts | Britannica. In: Encyclopædia Britannica. [online] Available at: https://www.britannica.com/science/optical-telescope [Accessed 1 Jun. 2025].

NASA (2024). Telescopes 101 - NASA Science. [online] science.nasa.gov. Available at: https://science.nasa.gov/universe/telescopes-101/ [Accessed 1 Jun. 2025].