Space Telescopes: What Are They Good For?

I've written many times about how I felt when I first saw the Ultra-Deep Field taken by the Hubble Space Telescope. That image changed me in ways I'm still coming to terms with.

There are so many galaxies in our universe, hundreds of billions, yet just over 100 years ago, we didn't even think other galaxies existed. We thought the Milky Way, our home galaxy, was the only one.

Can you believe it? We actually thought that.

I suppose it can be forgiven though because we simply didn't know better. I Imagine astronomers 100 years from now will be making fun of us and the things we don't know today.

It's true. We DON'T know what makes up over 95% of the universe. Normal matter, the stuff we can touch, taste, smell and otherwise perceive, constitutes only 4% of all that is.

There is good news though, we are learning more all the time and I think that in 100 years, we'll have it sorted out.

When Edwin Hubble first figured out that the "Andromeda Nebula" wasn't a nebula at all, but a galaxy, he forever expanded our boundaries. He moved the boundary of the universe from the confines of the Milky Way to something larger.

And he did it using a telescope on Mount Wilson, a telescope that was state of the art at the time, but is now just kinda quaint: a 100-inch reflector mounted high in the mountains in California. Hubble believed that the "spiral nebulae" he was looking at were island universes, and by measuring the variable stars within them, was able to determine that these nebulae were actually galaxies, like the Milky Way, and very far away.

Edwin Hubble single-handedly increased the size of the universe.

Over time, these large ground-based telescopes provided confirmation of not only Hubble's findings, but offered a myriad of discoveries in their own right. Larger and larger telescopes were built over the years and installed in more and more remote locations around the planet.

These remote locations were necessary to avoid all the pollution (both light and smog) required to see faint objects in the remote reaches of the universe.

So far, the largest ground-based telescope is in the Canary Islands, just off the coast of Spain, called the Gran Telescopio Canarias and measures 10.4 meters in diameter. There are similar-sized ones all over the world. I've even looked through some of them. Here's the 4 meter telescope on Cerro Tololo in Chile.

We've pretty much reached the limit of how large these telescopes can built, which means we're approaching the limit to what they can tell us about the cosmos. Building telescopes any larger than, say 10 meters, becomes counterproductive because the atmosphere becomes the limiting factor in what can be seen.

Telescopes are defined largely by how faint or how small an object they can see And by 'see' I'm talking about making out small details like individual stars or spiral arms. This is known as resolution, and is a measure of the smallest detail an optical instrument can provide. If you can see individual stars in a cluster, it is said to be resolved. If you can distinctly measure two stars in a close binary system, it is said to be resolved. Furthermore, if you can see the spiral arms of a galaxy at the edge of the universe, it is also resolved.

How faint (and how far away) an object a telescope can resolve is limited by a variety of factors: the diameter of the objective (the mirror or lens), the wavelength of the light being looked at, and the stuff between the object and the telescope, including the atmosphere if the telescope is on the ground.

For ground-based telescopes, you reach a point where the atmosphere becomes the limiting factor for what you can see, not the size of the mirror. We've pretty much reached that limit with the 8 to 10 meter sized telescopes.

Not only that, but there are some wavelengths we can't even see from the ground, like X-rays. The atmosphere blocks out things like that, which, I feel compelled to add, is a GOOD THING. I don't really want to live in an X-ray machine, I'd have to have clean underwear on all the time and who wants that?

So, to see fainter and farther away galaxies, and make out their structure, and see them in wavelengths not possible on the ground, we need to get rid of the atmosphere.

That's where space telescopes come in. The idea to put a telescope into space seems to have originated with Lyman Spitzer Jr., who, in 1965 first suggested the idea. It was from these beginnings that the first space telescope, the Hubble, was born.

Now we have many telescopes in space, all designed to look at a variety of wavelengths, including X-rays, gamma rays, infrared, microwave and regular old optical. These instruments are now only limited by how big we can make them: the bigger they are, the more (and farther back in time) we can see.

The telescopes we have in orbit around the Earth and Sun are all doing what Edwin Hubble did, expanding our boundaries and increasing our knowledge of our place in the heavens. We are driven to not only understanding the cosmos, but gathering information so we can make fun of what the astronomers 100 years ago didn't know.

It's just human nature really.

Space Telescope Videos:

• The James Webb Space Telescope
• How The Hubble Space Telescope Will Die
• The Hubble Deep Field in 3D