When you gaze at the night sky, you're not actually seeing stars as they are right now. Nope! You're seeing them as they were a long, long time ago1. This super cool trick is all thanks to how light travels through space.

The Speedy Messenger: Light's Constant Journey

Imagine light as tiny, super-fast messengers zipping across the universe. The most important thing to remember is that these light messengers always travel at a constant speed. Light is fast—300,000 kilometers per second—but space is vast.

Because stars and galaxies are unimaginably far away, the light they send out takes ages to reach our eyes on Earth! For example:

When you look at the Moon, you're seeing it as it looked 1.3 seconds ago.
If you spot the Big Dipper, the light from those stars began its journey to you anywhere from 79 to 125 years ago! So, you're literally seeing what that star looked like way back then.
Even for something super close, like an object just one meter away, you're seeing it as it was three billionths of a second ago3. That's way too fast for us to notice, but it proves the concept!

In space, the distances are so massive that the constant speed of light creates huge gaps in how we observe things, showing us into the past. It's the same idea in reverse: if someone from a galaxy 65 million light-years away looked at Earth with a super powerful telescope, they would see our planet as it was 65 million years ago, around the time the T-Rex went extinct! Interestingly, scholars in 14th-century India were already thinking about the speed of sunlight, and their ancient calculations were surprisingly close to what we know today.

The Expanding Universe and Redshift: Stretching Time!

Now, here's where the physics gets even wilder! The universe isn't just sitting still; it's expanding! Think of space itself as a giant, stretchy fabric. As this fabric stretches outwards, the light traveling through it also gets stretched5. This stretching of light waves is a real physics phenomenon called the Doppler effect. It's similar to how an ambulance siren's pitch changes as it zips past you – the sound waves get stretched and shortened.

With light, instead of pitch, it's the color of the wavelength that changes. When light waves get stretched out, they shift towards the red end of the spectrum, becoming "redder". This is known as redshift. The farther away a star or galaxy is, the more its light gets stretched and shifted towards red6. At some point, the waves get so long that they no longer appear as visible light to our eyes and slip into infrared light.

You can't see redshift with your naked eye because it only applies to objects that are really far away, and the color change is very slight. But for astronomers, understanding and accounting for redshift is super important when observing anything incredibly distant in the universe.

Peering into the Cosmic Dawn with Super Telescopes

To see things really far away – and thus, really far back in time – we need special tools!

The Hubble Space Telescope was built to see a small portion of the infrared spectrum. In 2016, Hubble observed a galaxy that was 32 billion light-years away, but because the universe has been stretching since that light left, we were actually looking at the galaxy as it was 13.4 billion years ago! This galaxy, called GNZ-11, is near Ursa Major, and its observation is the closest we've come to seeing the very birth of our universe.
Since Earth's atmosphere blocks some infrared light, telescopes in space are essential. This is why astrophysicists like Taylor Hutchison, who study distant galaxies that existed about a billion years after the Big Bang (around 13 billion years ago from our present day), rely on space observations.
The James Webb Space Telescope (JWST) is a serious game-changer for these kinds of observations because it observes from outside Earth's atmosphere and specializes partly in infrared light. It helps us see light from very distant galaxies that has been redshifted from ultraviolet light all the way into the near-infrared.

Astronomers and cosmologists are working right now to look so far into the cosmos that we might one day be able to see the very first light at the birth of the universe, nearly 13.8 billion years ago! They hope to see the supernovae of the first stars and even find the first galaxies ever formed.

So, every single time you look up at the stars, remember you're not just seeing twinkly lights; you're literally catching light waves that have been traveling across the vast, expanding fabric of space-time for ages, giving you a real-time glimpse into the cosmic past! How cool is that?

Fun Fact:

If aliens lived 65 million light-years away and had a powerful enough telescope, they’d be watching dinosaurs roam Earth right now. To them, humanity hasn’t even happened yet. Time lag in space is real—and wild.