February 27, 2020 0

The 1995 Hubble photo that changed astronomy

The 1995 Hubble photo that changed astronomy


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.”

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