Design your own telescope

Have you ever wondered how a telescope works? In this course you will learn how to use basic physical principles to design your own telescope. The course material is directly linked to geometric optics, reflection, refraction and Snell’s law.

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4 Lessons


The optical telescope has been the backbone of astronomy since it’s invention in the early 17th century. It helped to settle an old argument of whether the Earth or the Sun was at the centre of the Universe. Since then we have learned that the Universe has no centre. The Sun is but one out of a billion stars in a galaxy called the Milky Way. However, it has turned out to be a pretty exciting place.

In 1923, a junior astronomer named Edwin Hubble discovered another galaxy, which is now called Andromeda. From his observations, he learned that the stars in this galaxy were much further away than any other star in the Milky Way. He also realized that the Universe is expanding. Using modern telescopes, we have observed light from the most distant galaxies. This light has travelled about 13 billion years to reach us here on Earth.

Learning objectives

We need a big telescope to observe the furthest parts of the Universe. One of the biggest telescopes in the world is the Very Large Telescope in Chile, South America. It actually consists of four individual telescopes. Each one has a main mirror of 8.2 meters in diameter.

Technological advancements have helped us to create these large telescopes. However, it’s still the same basic physical principles that are used to design telescopes today. In this course, you will learn about these principles and how they can be applied to design your own telescope.

Curriculum links

  • Geometric optics.
  • Reflection.
  • Refraction.
  • Snell’s law.

This is our prototype course. So if you spot any bugs or issues please let us know.


The Andromeda Galaxy.

The Andromeda Galaxy. Credit: skeeze / Pixabay

This aerial shot of ESO’s Very Large Telescope array on top of the 2600-metre-high Cerro Paranal in the Chilean Atacama Desert beautifully shows the various stations for the mobile Auxiliary Telescopes. The largest structures are the enclosures of the four 8.2-metre Unit Telescopes of the VLT. In the middle lies the VLT Interferometer (VLTI) laboratory. Contrary to other large astronomical telescopes, the VLT was designed from the beginning with the use of interferometry as a major goal. The VLTI combines light captured by two or three 8.2-metre VLT Unit Telescopes, dramatically increasing the spatial resolution and showing fine details of a large variety of celestial objects. However, most of the time, the large telescopes are used for other research purposes. They are therefore only available for interferometric observations during a limited number of nights every year. Thus, in order to exploit the VLTI each night and to achieve the full potential of this unique setup, some other smaller, 1.8-metre dedicated telescopes were included into the overall VLT concept. These telescopes, known as the VLTI Auxiliary Telescopes (ATs), are mounted on tracks and can be placed at precisely defined “parking” observing positions on the observatory platform (seen along the lines in the image). From these positions, their light beams are fed into the VLTI laboratory via a complex system of reflecting mirrors mounted in an underground system of tunnels. Taken in 2005, this photo shows only two of the four ATs that are currently in operation. The enclosure on the upper right of the image will soon host the VLT Survey Telescope (VST).

The Very Large Telescope. Credit: ESO/G.Hüdepohl