If you are into astronomy and a passionate stargazer, you must have wondered about exoplanets. You must have pondered about the size that a telescope needs to be in order to see such a small object orbiting a star so far away.

Telescopes that can see exoplanets:

TelescopeDiameter Size
Anglo-Australian Telescope3.9 meter 
ESO Telescope3.6 meter
Very large telescope8.2 meter
Hubble Telescope2.4 meter
Kepler Telescope1.4 meter

Don’t worry! In this article, we’ll talk about how big a telescope needs to be in order to see the exoplanets.

What Is An Exoplanet?

An exoplanet or an extrasolar planet is a planet that orbits its star in its own solar system. The nearest solar system to us is Alpha Centauri. And Proxima Centauri, a planet orbiting Alpha Centauri, is the nearest exoplanet to us.

The Size A Telescope Needs To Be To See Exoplanets

Before knowing about the size of the telescope, we must know about the types of telescopes that are used to observe exoplanets.

There are mainly two types of telescopes that can detect and see exoplanets. They are:

  • Ground-Based Telescopes
  • Space-Based Telescopes

Ground-Based Telescope

Most of the telescopes in the world are ground-based. As the name implies, Ground-Based Telescopes are situated on the ground. They observe and look out for exoplanets from the surface of the earth.

Ground-Based Telescopes are limited because of the light pollution and the fact that it has to find planets penetrating through the earth’s atmosphere. They are also limited by their size.

Though there are a lot of ground-based telescopes, very few of them are able to detect exoplanets.

Some notable ground-based telescopes that played a crucial part in viewing exoplanets are

  • Anglo-Australian Telescope.
  • ESO Telescope.
  • Very large telescope.

Anglo-Australian Telescope

The 3.9-meter Anglo-Australian telescope situated in Australia has found 28 exoplanets ( till February 2014). It has a diameter of 3.9 meters and a focal length of 12.7 meters. It also has a surface area of 12 Sq.meters.

It uses optical fibers to gather light and then uses spectrography to analyze the light and hence detect planets.

Eso Telescope

The 3.6m Eso telescope situated at La Silla Observatory in Chile has paired with a HARPS (High Accuracy Radial Velocity Planet Searcher) spectrograph.

It has now discovered 130 exoplanets. The telescope has an aperture of 3.6 meters and a surface area of 8.6 Sq.meters.

Very Large Telescope

The Very Large Telescope situated in Chile is a set of two pairs of telescopes. Each of the four telescopes has a diameter of 8.2 meters. They can work individually and also in a group.

This telescope has a focal length of 120 meters. This is the first telescope that was able to image an exoplanet (2M1207b) directly.

Space-Based Telescope

Space-Based Telescopes look out for exoplanets staying outside the earth’s atmosphere. The telescopes that contributed the most to discovering exoplanets are:

  • Hubble Telescope
  • Kepler Telescope
  • Spitzer Telescope
  • TESS (Transiting Exoplanet Survey Satellite) Telescope

Hubble Telescope

Hubble is an extraordinary telescope. It is still contributing silently to space exploration. Though Hubble was not particularly built for finding exoplanets, it still managed to capture the first visual image of an exoplanet.

In 2008 a photograph of the exoplanet named “Fomalhaut b” was captured by the Hubble telescope. Hubble also managed to find organic molecules on an Exoplanet in the same year.

Hubble is 13.3 meters or 43.5 feet long telescope. It has a mirror with a diameter of 2.4 meters. It has a focal length of 57.6 meters and a focal ratio of f/24.

Hubble has a collecting area of 4.25 Sq.meters. It can be said Hubble is as big as a school bus.

Kepler Telescope

Kepler is definitely the telescope that contributed the most to searching for exoplanets. It managed to discover a whopping 2,662 exoplanets before being retired on October 30, 2018. Kepler was purposefully designed to discover and view exoplanets.

Kepler detected the presence of the exoplanets by observing slight obstruction of light caused by a planet crossing directly in between Kepler’s view and that planet’s star.

By observing the slight dip in luminosity, Kepler was able to detect the size of the exoplanet as well as the size of the star it orbits.

Kepler is 4.7 meters (15.3 feet) long and has a 0.95m mirror. It has a collecting area of 0.708 Sq.meters. It has a dimension of 4.7 m × 2.7 m or (15.4 ft × 8.9 ft).

Spitzer Telescope

Spitzer is also a very important telescope that helped us to view and detect numerous exoplanets. Spitzer uses infrared rays to detect and gain a perspective of the exoplanet. Spitzer discovered 7 exoplanets before being retired earlier this year on January 30.

Spitzer had a very sensitive infrared sensor, which is why despite being a very small telescope, it was able to detect this many exoplanets. It has a diameter of only 0.85 meters and a focal length of 10.2 meters.

Tess (Transiting Exoplanet Survey Satellite) Telescope

Tess space telescope was designed for the sole purpose of finding and observing exoplanets. Tess uses Transit Photometry Method to detect exoplanets. It mainly relies on its four cameras to detect exoplanets.

Tess has discovered 66 new exoplanets till now. And even more, exoplanets discovered by Tess are awaiting the approval of astronomers.

Tess does not use the conventional technique to produce an image. It uses advanced cameras to take pictures. Tess has a length of 3.7 meters or 12 feet. Its dimension is 3.7 × 1.2 × 1.5 m or 12 × 4 × 5 ft.

Its primary mirror is 1.4 meters in diameter. Tess has an entrance pupil diameter of 10.5 cm and a focal ratio of f/1.4.

James Webb Space Telescope

Although this telescope is not launched yet, it promises to bring a whole new dimension to exoplanet observations. James Webb is scheduled to launch on October 31, 2021. It will be launched as a replacement for the well-famed Hubble space telescope.

James Webb will use the latest infrared technology to observe exoplanets. It has a dimension of 20.197×14.162 meters or 66.26 ft × 46.46 ft.

James Webb’s main telescope has a diameter of 6.5 meters and a focal length of 131.4 meters. It also has a collecting area of 25.4 Sq.meters.


Both ground-based and space-based telescopes have contributed and are still contributing to detecting and viewing exoplanets. But both of them are very large in size. They are also very difficult to maintain and operate.

Finding and viewing exoplanets have to be done by professional astronomers using very sensitive and professional tools. It can not be done by using house telescopes.

Telescopes having a very large aperture and sensitive sensors are used in observing exoplanets.

Ground-based telescope observatories are large in size because they have to house an immense number of instruments. The primary telescope takes up most of the space on a Ground-based telescope observatory.

The telescope needs to be very big in size as it is trying to capture a very faint speck of light from a very long distance.

On the other hand, Space-based telescopes can not be very large in size because of the payload limitation of our rockets. But they have a very sensitive and powerful sensor to make up for it.

Their sensor and mirrors are also very large in size as they also have to capture as much information as they can to detect and watch out for exoplanets.

Hopefully, you are able to grasp an idea about the size that a telescope needs to be to see Exoplanets.