The farthest we can see into space is 46 billion light years away, thanks to the Hubble Space Telescope. But what does that actually mean? Let’s break it down step-by-step.
What is a light year?
A light year is a unit of distance, not time. It’s defined by how far light travels in one year.
Since light travels at 186,000 miles per second, a light year is equivalent to about 6 trillion miles. That’s a 6 with 12 zeros after it! Hard to imagine, right?
To put it in perspective, our Sun is about 8 light minutes away from Earth. That means it takes sunlight 8 minutes to travel the 93 million miles to reach us.
How far can we see unaided?
Without any telescopes or other instruments, the farthest we can see into space with the naked eye is about 4,000-6,000 light years away.
The most distant individual stars visible are around 1,500 light years away in the constellation Carina. Meanwhile, the Andromeda galaxy, our closest galactic neighbor, is 2.5 million light years away and can also be spotted unaided under dark skies.
How telescopes extend our vision
Telescopes dramatically increase how far we can see into space by collecting and magnifying more light. The bigger the telescope, the more light it collects and the farther it allows us to see.
Before Hubble launched in 1990, the farthest observed galaxies were about 6 billion light years away. Hubble expanded that vision tremendously thanks to its 94.5 inch primary mirror.
Notable Hubble discoveries
- 1996 – Hubble Deep Field image shows galaxies 12 billion light years away
- 2004 – Hubble Ultra Deep Field reveals galaxies 13 billion light years away
- 2009 – Hubble Extreme Deep Field sees galaxies 13.2 billion light years away
Each subsequent deep field imaged even fainter and more distant galaxies. Long exposure times, sometimes over 1 million seconds, were required to capture enough light.
New record: Over 13 billion light years
In 2016, Hubble broke the cosmic distance record again. Astronomers used Hubble along with other space- and ground-based telescopes to spot galaxy GN-z11, a staggering 13.4 billion light years away.
This now puts Hubble’s observational reach at 13.4 billion light years in any direction, or about 96% of the way back to the Big Bang 13.8 billion years ago.
How can we see 46 billion light years?
If the observable universe is 13.4 billion light years in radius, how can we now see 46 billion light years away? The answer lies in the expansion of space.
As light from distant galaxies travels to Earth, the universe continues expanding. By the time the light arrives, those galaxies have receded even farther away.
So the light has traveled 13.4 billion light years, but the distance to those galaxies is now much farther due to expansion – up to 46 billion light years!
The expanding universe
To help visualize this, imagine raisins spreading out as a dough expands. The farther raisins started out, the farther away they end up from us due to the dough’s expansion.
| Time | Distance then | Distance now |
|---|---|---|
| 13.4 billion years ago | 13.4 billion light years | 46 billion light years |
So we see those distant galaxies as they looked 13.4 billion years ago, when their light started the long journey to us. But they have since receded to 46 billion light years away.
Future telescopes to see even farther
What’s next for our vision into deep space? Hubble’s successor, the James Webb Space Telescope, launched in 2021 and has already revealed galaxies over 13.5 billion light years away.
As Webb continues peering back towards the Big Bang, it could potentially see over 100 billion light years across space and over 13.6 billion years back in time.
Upcoming telescopes
- James Webb Space Telescope – launched 2021
- Nancy Grace Roman Space Telescope – expected 2025
- Extremely Large Telescope – first light expected 2027
Bigger mirrors and advanced infrared imaging will push the observable limits even farther in the coming decades. Exciting discoveries surely await!
Conclusion
While unaided human vision is limited to just a few thousand light years, telescopes have now allowed us to see out to 46 billion light years away – 96% of the way back to the Big Bang. Upcoming telescopes will push the depth of our vision even farther back in time and across the ever-expanding universe. Discoveries yet unknown are sure to reveal even more secrets of our vast cosmos.