When we look up at the night sky, everything looks close. But in reality, stars and galaxies are incredibly far away. Knowing how far something is in space helps scientists understand how big it is, how old it is, and even how the universe is expanding.

So how do we measure something that we can't even travel to? It turns out, we have a few very smart ways.

The first step: parallax

One of the earliest and simplest ways to measure the distance to nearby stars is a method called parallax. It works just like how our eyes judge distance. If you hold out your finger and close one eye at a time, your finger seems to move. Astronomers do the same thing by observing a star from two positions—six months apart—when Earth is on opposite sides of its orbit around the Sun.

The tiny shift in the star's position, compared to more distant background stars, helps calculate its distance using simple geometry. This technique is very accurate—but only for stars that are relatively close.

Going further with brightness

For stars that are too far away for parallax, astronomers use brightness as a clue. There are some stars—like Cepheid variables—that pulse in brightness in a regular pattern. We've figured out a strong link between how long they pulse and how bright they truly are.

So if we see one of these stars in a far-off star system and measure how bright it appears to us, we can compare that with its actual brightness to calculate how far away it must be. It's like seeing a car's headlights at night: the dimmer they look, the farther the car must be.

Supernovae: nature's bright rulers

Another amazing tool is a certain type of exploding star called a Type Ia supernova. These always explode with about the same brightness, making them perfect "standard candles." If we spot one in a distant star system, its brightness can tell us how far away that star system is. This method has helped us measure extremely far distances—billions of light-years away!

Using redshift to go deeper

When light travels across space, it stretches if the object is moving away from us. This makes the light appear more red, which is why we call this effect redshift. The more redshift we see, the faster the object is moving away—and the farther it is.

By measuring how much a galaxy's light is shifted toward red, astronomers can estimate its distance. This method is especially useful for objects that are too far away to use parallax or brightness techniques.

Putting it all together: the cosmic ladder

Each of these methods helps us reach a little farther into space. Together, they form what scientists call a cosmic distance ladder. We use parallax to measure nearby stars. Then we use those stars to calibrate Cepheid variables. From there, we jump to supernovae and redshift to reach the most distant parts of the universe.

It's a bit like using a tape measure that keeps growing longer with each step.

So, how far can we see?

Thanks to these tools, we can now measure distances to galaxies that are over 13 billion light-years away. That means we're seeing light that left those galaxies just a few hundred million years after the Big Start. In other words, we're looking back in time!

What do you think?

Isn't it amazing how we can figure out the size of the universe from our tiny planet? Which method surprised you the most—parallax, brightness, or redshift? If you could use a telescope, which star or star system would you want to measure? Let us know what fascinates you about space and distance—we'd love to hear your thoughts!