Telescopes. Refractors and reflectors

Do you know the basics of telescopes and their types?

The online telescope simulations on this page show the principle of operation of refracting (Keplerian and Galilean) and reflecting (Newtonian) telescopes.

A telescope is an optical instrument used to observe and study distant objects in space, such as stars, planets, galaxies and other celestial bodies. Through their design and features, telescopes allow astronomers to gather light and increase the visibility of astronomical objects, revealing details and phenomena that would otherwise be invisible to the naked eye.

Telescopes can be classified into two main categories: refractors and reflectors. Refracting telescopes use lenses to collect and focus light, while reflecting telescopes employ curved mirrors. Both types have advantages and disadvantages, and their choice depends on the specific observing objectives.

The size of the telescope is a critical factor in its performance. The larger the diameter of the objective or main mirror, the more light it can collect and, therefore, the higher the quality of the image obtained. Professional telescopes typically have diameters of several meters and are found in astronomical observatories around the world.

In addition to light collection, many modern telescopes are equipped with advanced instruments and devices to analyze the light received. These include spectrographs to study the chemical composition of objects, digital cameras to capture high-resolution images, and detectors of electromagnetic waves beyond the visible spectrum, such as X-rays and infrared radiation.

The development of technology has enabled the use of space telescopes, such as the Hubble Space Telescope, which is located outside the Earth’s atmosphere and can capture sharp, detailed images without the distortions caused by the atmosphere. These space telescopes have revolutionized our understanding of the universe and have provided amazing images of distant galaxies and cosmic phenomena.

The study and observation with telescopes have led to important discoveries in astronomy, such as the identification of exoplanets, the measurement of the expansion of the universe, and the understanding of black holes. Telescopes continue to be fundamental tools for astronomers in their search for answers about the origin, evolution and nature of the cosmos.

In summary, the online telescope simulations on this page are very useful to understand the basic operation of a telescope. Check them out and you’re sure to like them!

Below are several simulations and other educational resources, which can also serve as very illustrative examples. In addition, a selection of books and courses is included to help you broaden your knowledge of this subject

Refracting telescope (Keplerian and Galilean)


A telescope that uses only the refraction of a lens is called a refracting telescope. There are two types, the Galilean telescope and the Keplerian telescope. The Galilean telescope or earth telescope consists of a convex objective and a concave eyepiece. The Keplerian telescope has a convex objective and convex eyepiece. Most astronomical telescopes in use today are Keplerian telescopes, whose operation is as we can see in the first of our online telescope simulations..
Click here to start the simulation

Reflecting telescope (Newtonian)


The condensation of a telescope is closely related to the size of the objective lens. This leads to a preference for larger telescopes. However, refracting telescopes cannot be made as large as desired. The telescope that solves this problem is the reflecting telescope, which is currently the most widely used telescope for astronomical observation, and whose operation is the one we can observe in this last of our online telescope simulations..
Click here to start the simulation

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