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Looking up into the night sky, it seems like you can see forever. If you use binoculars or a telescope that feeling is, literally, magnified - you can see thousands, millions of stars.
But what you're seeing is barely scratching the depths of the Universe. You're looking out a few thousand light years into a galaxy a hundred thousand light years across, in a Universe where we can see distant galaxies over 10 billion light years away.
We build bigger telescopes so we can see those far-flung objects, and we even put them in space so our bothersome atmosphere doesn't interfere with the view. The most famous is of course the Hubble Space Telescope. It's hard to describe just how much of an impact this Grande Dame of astronomy has had on our perception of the Universe... though looking into the Hubble Deep Fields, you get a glimmer of it. In 1995, Hubble stared at one spot in space for over 140 hours, creating the first Deep Field. It revealed thousands of galaxies at tremendous distance, showing us that the sky is filled with galaxies.
The region of the sky for the first Deep Field was chosen because it was nearly devoid of stars and known galaxies, objects that would interfere with their more distant brethren. But what does that field look like from the ground? Astronomer Detlef Hartmann decided to tackle this question, and has done us all a favor by showing us. Using a 44 cm (17") telescope he built himself, he took an incredible 247 five-minute images to create this extraordinary picture with a total of 20 hours of exposure... and then lets it morph into the actual Hubble Deep Field to compare them:
Let me be clear: Detlef's image is amazing. It's a tremendous effort by an "amateur"*, and shows dozens of the galaxies (and the same scattered handful of stars) in the Hubble image. It's an amazing achievement. A bigger telescope would show more galaxies, of course, and resolve them more clearly, but even the biggest telescope located on the surface of our planet needs to peer through the soup of air above it, which dims the faintest galaxies into obscurity. You need to get above our atmosphere to see the cosmos as clearly as possible.
And when you do, look at what Hubble shows us. That tiny region of the sky - easily blocked by a grain of sand held at arm's length - contains thousands of galaxies, each a sprawling city of billions of stars. It represents a relatively random part of the sky, so you can expect to see something like it no matter where you point a telescope... and that picture shows just one 24-millionth of the entire sky. The implication is clear: there are hundreds of billions of galaxies in our Universe. That in turn means there are sextillions of stars, each a Sun, and many, if not most, circled by a retinue of planets.
It's the most ironic aspect of any science I know: it crushes my sense of scale and ego into dust, but also fills me with wonder and amazement that we can know such things, and be a part of it.
As is so often the case in science, you don't know what you'll get when you build a new instrument. You build it for one reason or for many, but later on new applications arise, new ways to use it. And sometimes, years down the road, it's utilized in a just such a new way which profoundly changes how you see the Universe, how you see yourself and your place in it, and in a way you had may have only had an inkling of when you started out. The Hubble Deep Fields are perfect examples of this.
We knew intellectually the Universe was deep, and our place in it infinitesimal yet rare and beautiful. But Hubble showed that to us.
Image credits: R. Williams (STScI), the Hubble Deep Field Team and NASA; Detlef Hartmann. My deep thanks to Salvatore Iovene (who hosts AstroBin where Detlef's image is displayed) for letting me know about this amazing work.
* Oh, that word. Detlef built his own 'scope, took hundreds of these images, then combined them in a painstaking and difficult process that probably took him many, many hours. The word "amateur" has many connotations, but as usual here when I use it, I simply mean someone who is not a career astronomer. Detlef clearly has it going on.
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