How far back in time can we see through a telescope?

Horsehead Nebula & Flame Nebula in H-alpha – Picture by Isabel Streit 2022

How far back in time can we see through a telescope?

I have been contacted in November 2021 for an interview with a well-known international news network. The occasion was supposedly the launch of the James Webb Space Telescope (25 Dec 2021), the latter being a joint-venture by NASA, ESA and the CSA with Northrop Grumman playing a key part in it – a few facts that, unfortunately, tend to be forgotten. 

However, the interview has never been published for reasons I ignore and frankly don’t care so much about. But as always, I prepared myself, dedicated quite a few hours researching and getting ready. 

One theme I prepared for is the question of how far back in time can we see through a telescope, and for that matter, my refractor, a Takahashi FSQ-85 EDX (450 mm). While I’m not an astronomer, I’d like to present you a few facts I gathered. If you have any comments and corrections, please feel free to send me an email to: contact(at)

Earth–Moon distance

Let’s start with the Earth-Moon distance (Lunar distance LD or Δ ⊕ L). It’s roughly 400’000 km, or a quarter of 1.28 light seconds. Roughly 30x Earth’s diameter (which is 12’742 km). The actual distance varies over the course of the orbit of the Moon, from 356.500 km at perigree to 406,700 km at apogee. 

Distance of 1 light year

1 light year is the distance travelled by light in 1 year. It is roughly 10 billion kilometers or 1012 km. In astronomy, we also express distances in parsec (pc). 1 parsec is the equivalent of 3.26 light years or 206’265 AU; for AU see below). So for example the open star cluster of the Pleiades (Messier 45) as we see it today is how it looked 400 years ago in 1622 – early modern period of Europe (Baroque, Spanish Golden Age, the Scientific Revolution, the Thirty Year’s War, European Colonization of the Americas; In the Islamic world, the Ottoman, Safavid and Mughal empires grew in strength; In Japan, Tokugawa Ieyasu established the Tokugawa shogunate; In China, collapse of the Ming dynasty). And if we were living in 1622, they would look like in 1222.

Open Star Cluster
The Pleiades – picture by Isabel Streit 2022

Astronomical Units

In astronomy, we also express distances in Astronomical Units (AU), especially for calculations within our solar system. 1 AU is roughly the distance from Earth to the Sun, about 150 million km (93 million miles) or ~8 light minutes. To recapitulate, the Moon is at roughly 400’000 km from Earth, the Sun at 150 million km. The Sun is therefore 375x further away from Earth than the Moon.

Some distances in ly to well known deep sky objects

To give you some examples of distances, here a list with well known so called “deep sky objects”:

  • The Pleiades – Messier 45: 400 ly or 125 pc
  • Messier 44 – The Beehive Cluster: 577 ly or 176 pc
  • X Persei: 7’500 ly or 2’300 pc
  • H Persei: 7’200 ly or 2’200 pc
  • Messier 13 – Hercules Globular Cluster: 22.2 kly or 6.8 kpc
  • Messier 31 – Andromeda Galaxy : 2.5 mly or 765 kpc
  • Messier 66: 31 mly or 9.6 mpc
  • Virgo A – Messier 87: 53.5 ± 1.6 mly or 16.4 ± 0.5 Mpc

Age of the Universe and when Webb Space comes into the game

Source: James Webb Space Telescope Media Kit

Now I have thrown a lot of numbers at you and I haven’t replied to the question of how far I can see with my refractor telescope. Before we come to this question, let’s think of what is the estimated age of the Universe. It’s estimated to be 14 billion years old. 

With my telescope I can take pictures of Messier 66, a spiral galaxy 31 million light years away while still being able to see that it is indeed a galaxy. Messier 66 is part of a small group of galaxies and a member of the so called the “Leo Triplet” because it appears in the Constellation of Leo. Of course, I can take pictures of fainter and more distant objects (faint and distance not being the same). 

M66 Group in Leo

The James Webb Space Telescope will observe a part of space and time when the very first stars and galaxies were formed, over 13.5 billion years ago. Webb is designed “see” the infrared light of the universes very first luminous objects. To conclude, my limit is of recognizing the shape of a celestial object is at around 31 million light years ago. Webb’s limit is at 13.5 billion ly ago. That’s truly overwhelming!


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