Since the Hubble Space Telescope went into orbit back in April 1990,
it has sent back a ton of incredible photos.
Each has its own story, but one of Hubble’s greatest images is this
one, from 1995.
This is a snapshot of nearly the entire history of the universe - and the first of its kind.
The Hubble Deep Field is an unusual image that came from an unusual process.
Typically astronomers apply to use Hubble to look at a particular known object.
“You want to study a star?
Okay you know what star you’re going to study. You point the telescope at that star.”
That’s Robert Williams.
He became the director of the telescope in 1993.
It was his decision to create the Deep Field image by pointing the telescope at nothing
in particular.
“What we're doing basically was just the opposite — we're trying to find a sort of
indiscriminate area of sky where no observation had been made before.”
They wanted to test how well Hubble could survey very distant galaxies.
But they didn’t know what they’d see.
And It wasn’t a great time to be trying new things.
“After spending 2 billion dollars for 12 years, to have this kind of unexpected, very
large mistake take place..”
The Hubble team was still repairing the reputation of the telescope after a flaw in the main
mirror produced blurry images for nearly three years.
“We were the brunt of jokes and the newspapers, political cartoons you know Johnny Carson
show. NASA was being made fun of for having made such a monumental screw up
of such an expensive project.”
NASA sent astronauts on a 5-day mission to install a module that would fix the problem.
And it worked.
So Williams’ team spent 1995 planning the deep field observation.
For one thing, they had to decide where to point the telescope.
The goal was to see far beyond our galaxy, so the spot needed to be away from the galactic
plane of the Milky Way and away from any known large galaxy clusters.
They didn’t want anything bright to block the view.
And to get continuous observations, it needed to be a location that wouldn’t
be obscured when Hubble went around Earth, as it does every hour and a half or so.
They settled on a region just above the big dipper -- a dark, unremarkable, peephole into
the universe.
The field of view was extremely narrow.
Astronomers measure the apparent size of objects in the sky in angular degrees, and a degree
can be divided into 60 arcminutes.
From Earth, the moon is about half a degree across, around 30 arcminutes.
But the area that Hubble photographed was just 2.6 arcminutes across.
“A little larger than a pinhead at arm's length.
So it’s a teeny patch of sky.”
The observations began on December, 18, 1995, collecting 4 different wavelengths of light.
And over the next 10 days the telescope took 342 images of that teeny patch of sky.
“We were relieved that we are getting good data but we had to keep adding it up and so
it wasn't until ten days that we realized oh, we really got something.”
There are a few nearby stars in the image but pretty much all the other objects here,
including these tiny blue dots -- they’re galaxies.
The light from these different galaxies has been traveling for vastly different amounts
of time so the furthest galaxies are shown pretty early in their evolution, more than
12 billion years ago.
That’s just a billion and a half years after the big bang.
It’s as if you could point a telescope across the earth and actually photograph ancient
Egypt, with a neanderthal in the background and then further back there’s a dinosaur.
The research team sampled another tiny spot two years later, this time in the southern sky.
“We wanted to know okay then we got one spot of this you never know maybe it was some
weird spot and so we thought it was important to repeat the observation.”
The datasets boosted estimates of the total number of galaxies.
They allowed researchers to track the history of star formation through the universe.
And they helped confirm the bottom-up theory of galaxy formation, by revealing galaxies
that are small and irregular early in their evolution.
But one of the most important legacies of the Hubble Deep Field is how it changed the
culture of astronomy.
“Until this time astronomy had a history of people taking the data and keeping it to
themselves until they had fully analyzed it after all this was intellectual property.”
Instead of hoarding the discoveries embedded in the dataset, Williams and his team formatted
and released it immediately to the wider scientific community.
It’s been cited in hundreds of papers.
“Nowadays it is so much more common for people to take interesting observations and
make the data available to the public even though they might have a right to keep it
for a certain period of time to themselves.”
Thanks to servicing missions that installed more advanced cameras, Hubble has since made
even deeper deep field images, and those data too, were released to the public.
“I think it it moves forward the march of human understanding human knowledge tremendously
and the Hubble deep field did that.”