The Hubble Space Telescope is one of the most famous telescopes in the world.

Oops, excuse me—one of the most famous telescopes built.

Hubble, after all, is certainly not in this world. Unless you call the universe the “world,” it’s about as far from being in this world as you can get. It’s in space.

Hubble isn’t that different from an ordinary, ground telescope. It’s only as big as a bus. There are bigger optical telescopes. Its mirror is 2.4 m across—hardly an achievement by modern-day standards.

Palomar Observatory, which was the biggest telescope in the world when it was built, has better optics than Hubble, meaning its images are a bit crisper.

But that doesn’t keep astronomers from continuing to use Hubble. In fact, if you want to use Hubble, you have to get in line—it hardly has time to complete all the projects astronomers ask of it, even observing the night sky 24/7.

So why is Hubble so useful?

Well, it’s a telescope in space.

And…what’s so great about that?

I don’t know if you’ve read or recall my post on the powers of a telescope, but I mentioned way back then that no matter how good your telescope is, no matter how big, no matter how expensive, its quality will always be limited by the atmosphere.

Bigger telescopes have more light-gathering power, which increases resolution (ability to see detail). And interferometry can increase resolution a bit more without making insanely expensive telescopes.

But no matter what we do to improve our telescopes, the atmosphere is always there, scattering light before it reaches us.

Unless we put telescopes above the atmosphere.

Hubble’s optics may not be quite as good as Palomar’s or other large telescopes. Its light-gathering power may be relatively low for professional astronomy. But it has an advantage no telescope on Earth has. It doesn’t have to look through the atmosphere.

Have you ever looked through a telescope at an object near the horizon?

Any object appearing near the horizon in the sky has more atmosphere to pass through to reach you. It’s why stars near the horizon might seem to twinkle on a night with particularly bad “seeing,” which is what astronomers call the atmospheric conditions.

Notice how Jupiter doesn’t look too crisp here? Its bands are extra fuzzy. It’s nowhere close to the detail we could get from a space telescope…

Now that’s what I call detail.

You will never see an image like this through an Earth-based optical telescope. Not even if you get to look through an amateur astronomer’s telescope at a public outreach event. Not even if you get lucky enough to look through an observatory’s telescope.

Space telescopes, like the Hubble Space Telescope, don’t have to look through the atmosphere. Light doesn’t scatter before reaching its optics. And as a result, you get that much more detail.

Hubble has taken a number of images that wouldn’t have been possible from within Earth’s atmosphere.

Here’s Mars as it might appear through a ground telescope…

And here’s Mars through Hubble.

Much more crisp, huh?

Because it has such good resolution, Hubble has been able to make a number of observations that have fueled astronomy research. For instance, this dust-filled galaxy.

This is the kind of resolution we can’t get from ground telescopes. We can see galaxies alright, but they look like little more than fuzzy blobs.

Through Hubble—or, indeed, any optical space telescope—you can really see detail.

It takes this kind of detail to make the discoveries astronomers crave.

Remember, we can’t reach out and touch the stars. Humans have gotten as far as the moon. Spacecraft have flown to the edge of the solar system. But the nearest star is still 4.2 light-years away.

You’d be surprised just how backwater our little planet is. Our Voyager 1 spacecraft took a solar system selfie that shows us just how tiny Earth is.

As Carl Sagan said…

“Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every ‘superstar,’ every ‘supreme leader,’ every saint and sinner in the history of our species lived there—on a mote of dust suspended in a sunbeam.”

Seriously. That’s how insignificant our planet is just from the edge of the solar system.

This is why astronomers depend on telescopes to collect radiation from those distant corners of the universe. Without light, we know nothing of the universe. There’s no sample in a laboratory labeled “stardust.”

And so we do the best we can to gather radiation. The more detail we can make out from that radiation, the better.

That’s the mission of any space telescope. And Hubble doesn’t stop with planets and galaxies—it has taken photos of some of the most obscure cosmic objects we know of.

This is a nebula around an aging star. The red star in the middle is the aging one—you can tell by its color. The nebula is a cloud of dust and gas, containing everything the younger stars nearby need to start a new solar system.

The universe is vast. But space telescopes like Hubble can help us see farther out in the darkness of space, expanding our horizons for discovery.

And Hubble is far from the only one of its kind. I’ll cover a few other space telescopes in my next few posts.