Hubble: The people's telescope at 25
How the space telescope has changed astronomy and brought the cosmos into people’s living rooms.
It was not a good moment for Hubble. The space telescope had just been launched into orbit two months earlier amid repeated pronouncements from scientists about how it would “revolutionize” astronomy.
Now here it was, circling high above Earth, with a defective main mirror. The year was 1990. The United States was edging toward recession, Iraq was preparing to invade Kuwait, and the National Aeronautics and Space Administration was only four years past its worst disaster in history – the breakup of the space shuttle Challenger. Couldn’t the engineers at least get it right with Hubble?
Editorial cartoonists lampooned the $1.5 billion telescope as designed by the nearsighted cartoon character Mr. Magoo. “Everyone was despondent,” recalls Brad Whitmore, an astronomer who joined the Space Telescope Science Institute here in 1983.
Yet Hubble still showed promise, if the flaw could be fixed. Mistakes in shaping the mirror had occurred away from its center, where it could still produce sharp images. As technicians worked to get the best pictures they could out of Hubble, they trained the telescope on what ground-based observatories recorded as a mysterious bright blotch surrounded by a few stars in 30 Doradus, a nebula 163,000 light-years away.
The image Hubble beamed back triggered a buzz. “You started hearing rumors in the hall – there’s this calibration observation of 30 Doradus that is like nothing you’ve ever seen!” recalls Dr. Whitmore. Hubble revealed the blotch as a swarm of individual stars.
Eventually, images like this, coupled with a derring-do correction of the mirror problem three years later, helped salvage Hubble’s reputation – and NASA’s. The ridicule-to-redemption story is an apt metaphor for the Hubble Space Telescope 25 years after it was first sent into space to peer at the cosmos.
Although the orbital observatory has endured its share of problems, it has overcome the setbacks to emerge as one of the world’s most important astronomical instruments since the tiny telescope Galileo turned toward the heavens.
As astrophysicist Mario Livio puts it: Hubble “is arguably the most successful experiment in the history of science.”
In an age when spacecraft scout the moons of Jupiter and physicists routinely probe the very nature of matter in cathedral-size subterranean halls at the European Organization for Nuclear Research (CERN), that’s quite an assertion. While not every scientist might agree with his assessment, few would dispute that Hubble has had a profound impact on the science and culture of astronomy – and become a symbol of cutting-edge research.
CERN’s Large Hadron Collider has been dubbed the Hubble of physics. As new ground-based telescopes have come on line with sophisticated new technology to scan the heavens, their point of comparison has been one other “eye” on the universe – Hubble.
Yet the orbital observatory has done more than make discoveries and help confirm existing theories. Dubbed the “people’s telescope,” it has provided the raw material for astronomical images that some art historians have likened to the Romantic landscapes captured in 19th-century paintings and photographs of the American West. It has brought the cosmos into classrooms and living rooms around the world.
Hubble’s popularity also stems in part from the drama surrounding it – from what University of Maryland, Baltimore County, historian Joseph Tatarewicz calls a “Perils of Pauline” saga with emotional highs and lows, such as the botched-mirror episode.
From its conception onward, each time Hubble hit a low, it rebounded, Dr. Tatarewicz says, “but before it rebounded, to one degree or another, the future of the agency and spaceflight hung on it. It’s just a good story.”
The concept for a space telescope first appeared in 1922 in a dissertation that German rocket pioneer Hermann Oberth presented in hopes of earning his PhD. Historians point out that his thesis, “The Rocket into Interplanetary Space,” initially was rejected as being too utopian.
The logic behind his idea was hard to refute, however. A telescope either in orbit or in deep space could provide images far more detailed than those from ground-based telescopes. Even on the clearest nights, Earth’s atmosphere distorts starlight, limiting the level of detail ground-based telescopes operating at visible wavelengths can reveal. Water vapor and ozone in the atmosphere also block nearly all of the infrared and ultraviolet light that carries yet more information about star birth, galaxies, and extrasolar planets.
Parked in an orbit 300 miles above Earth, Hubble was designed to avoid those limitations and provide crisp images and gather spectra with unprecedented levels of detail. During the telescope’s construction, Tatarewicz says, he and colleagues would sometimes marvel at the claims Hubble supporters were making about what the telescope was going to achieve.
“We occasionally would say the hype is getting out of hand,” he recalls. “The irony is that it has exceeded expectations on almost everything you can think of.”
One of Hubble’s initial tasks was to pin down the current expansion rate of the universe, a number known as the Hubble constant. This was one of three must-do projects astronomers sought to accomplish in order to declare the observatory a success should it fail to survive its 15-year design life. The Hubble constant is a critical piece of information for estimating the age of the universe, currently pegged at 13.8 billion years old.
Changes in the “constant” over cosmological time yield clues about the cosmos’s future. Depending on the amount of mass the universe contains, it will either eventually collapse under the influence of its collective gravity, continue to expand at a steady clip, or gradually slow in its expansion.
The problem: Estimates of the Hubble constant’s value differed by as much as 100 percent. The telescope’s role was to take measurements that would drive that uncertainty down to 10 percent. A team led by Wendy Freedman, at the time an astronomer with the Carnegie Observatories in Pasadena, Calif., took the requisite optical measurements – using stars known as Cepheid variables as beacons for gauging distances – and published the final results in 2001. Hubble’s observations are now being harnessed to reduce the uncertainties down to around 2 percent.
In using the team’s results to calculate the universe’s age, Dr. Freedman’s team had to take into account a stunning discovery to which Hubble also contributed: the universe is expanding at an ever faster rate. The breakthrough came as two teams were using the light from a particular type of supernova to help estimate the universe’s expansion rate.
At the time, estimates of the total mass and energy in the universe pointed to a cosmos whose expansion should slow as it ages, although it would never stop completely. When the teams measured the brightness of supernovae in the distant universe, the supernovae were dimmer than they should have been if the expansion were slowing. After sorting through the possible causes for the dimming, the researchers realized that the expansion was speeding up, driven by what has come to be known as dark energy.
Observations from ground-based telescopes as well as from Hubble provided the vast majority of the data used for each team’s initial reports on the discovery, which were published in 1998 and 1999. The discovery earned Nobel Prizes for the leaders of the two teams. Adam Riess, then at the University of California at Berkeley and Australia astronomer Brian Schmidt, split half the prize money, while astrophysicist Saul Perlmutter, also at Berkeley, garnered the other half.
Hubble’s data have since provided strong confirmation of the accelerating expansion and have established that dark energy began to assert itself about 9 billion years ago, an observation that has helped narrow the range of explanations for dark energy.
Such findings highlight the telescope’s history of contributing to discoveries, providing critical confirmation of earlier observations, and revealing fresh insights.
“Sometimes people build a small instrument that is going after one question and it answers that question,” says Dr. Livio, who came to the Space Telescope Science Institute in 1991 and has headed its science division. He adds that Hubble “has answered a few such questions. But “most of the time it has provided the crucial piece of information that helped transform suggestive results from other things into facts.”
Yet, aided by its longevity, Hubble has also produced its share of “firsts.” It has provided, for instance, the first images of infant galaxies and galaxy fragments in the early universe, and was the first telescope to detect chemical elements in the atmosphere of a planet orbiting another star.
By some estimates, Hubble is arguably the most scientifically productive telescope in history. The number of research papers using Hubble data and published in major science journals each year has risen relentlessly since 1996, according to an analysis by the European Southern Observatory. Indeed, since 1997, the annual number of papers using Hubble data has far outpaced the number of those using data from 15 other notable space and ground-based telescopes.
Thomas Lloyd, band director at Columbus State Community College in Columbus, Ohio, was hunting for pieces the band could perform at the city’s bicentennial celebration in 2012. Born in the 1950s, “I was fascinated by the space program,” he recalls.
Perusing a journal for music educators, he saw an ad for videos that came with musical scores. Bands or choirs perform the music live while the video plays behind them. The package, featuring a five-minute film on Hubble and its dramatic images of the cosmos, was too good to pass up.
“It’s a good piece of music,” he says. But “even without the music, people would be fascinated by the images. There’s the beauty of the images, but there’s also the awe. It is totally beyond comprehension. You feel that way when you hear Beethoven’s Fifth Symphony.”
The performance is one small example of how Hubble and its images have transcended the confines of science conferences to become a global ambassador for astronomy. When scientists hunting for the Higgs boson – the particle associated with a field that gives other subatomic particles their mass – announced in 2012 that they had found it, “people all over the world got excited, says Livio. “But with Hubble, they got excited numerous times. When you count all of that together, Hubble is truly remarkable.”
Part of Hubble’s allure lies in the melodrama that has often surrounded the telescope. Few events captured the Shakespearean theater better than the misshapen mirror incident in 1990. These days, the event seems like a footnote. For anyone in high school or college, the only Hubble they know does nothing but crank out the cosmos’s greatest hits, notes Carol Christian, outreach scientist at the Space Telescope Science Institute.
“It’s like, ‘Oh, did that happen? Oh, interesting,’ ” and they quickly move on.
At the time, though, the event was devastating. Engineers floated several ideas for fixing Hubble’s vision. The inspiration for the final solution, however, came from an unlikely source – a shower head.
James Crocker, then an engineer with the Hubble program, was in Germany at a strategy meeting with representatives from the European Space Agency, NASA’s international partner on Hubble. He noticed that the shower nozzle in his hotel bathroom moved via adjustable rods – just the kind of mechanism that could deploy a proposed set of mirrors to correct Hubble’s focus. COSTAR, installed during Hubble’s first servicing mission in 1993, was born. It corrected Hubble’s vision for two of three instruments, while a replacement for the Wide Field and Planetary Camera carried its own corrective mirrors.
“Some guy goes into a shower in Germany, fiddles with the articulated joint of the shower head, and says, ‘I know how to do this now.’ You can’t make this stuff up,” says the University of Maryland’s Tatarewicz.
Since its launch into orbit on April 25, 1990, Hubble has added one indelible image after another to humanity’s collection of postcards from the cosmos, which have continued to make significant contributions to science well after their arrival.
The telescope has played a key role in democratizing astronomy by making information widely available within a relatively short period after it has been collected. It has also fed an enormous archive of information and images – more than 100 million – that generates more science today than during initial observations. “There are more papers written today based on archival data than on new data,” Livio says.
In March, the Space Telescope Science Institute announced that all of this material had been collected into a vast online compendium known as the Hubble Source Catalog – a resource that allows astronomers to quickly search for objects and their characteristics.
“We’re not building this for the next year or two or three,” says Whitmore, who has headed the development team that produced the catalog. “We’re doing this for the next decade, 20, 30, 50 years....”
But Hubble will be about more than just its archives. As the observatory heads into what is likely to be its final decade, astronomers are building a bucket list of future projects.
The effort is known as Hubble 2020. The goal is to expand the telescope’s already considerable legacy with projects that will make their own discoveries as well as complement observations from the James Webb Space Telescope, scheduled for launch in 2018.
For instance, some astronomers have recommended using Hubble for a concerted effort to analyze the atmosphere of planets orbiting stars. Others have suggested tapping it to take precise measurements of the internal and external motions of dwarf galaxies and streams of stars as a window on galaxy evolution and dark matter.
Not a bad start on a final wish list for an observatory that was once thought headed for retirement. In 2000, NASA was expecting to eventually send up a space shuttle and return the telescope to Earth around 2010. As of 2015, Hubble is still scanning the heavens, while NASA’s three once-operational shuttles are now museum pieces.
That longevity, of course, stems from Hubble’s design and NASA’s ability to send up astronauts and hardware to make periodic repairs and upgrades. The last of five servicing missions, in 2009, “was very ambitious,” notes Dr. Christian. And it left the venerable telescope in remarkable shape.
Astronauts repaired two of the telescope’s workhorse instruments, the Space Telescope Imaging Spectrometer and the Advanced Camera for Surveys. They replaced the telescope’s second wide-field camera with a third, more capable version. And they installed the Cosmic Origins Spectrograph, which will extend Hubble’s ability to gather information on celestial objects from the near-infrared and visible range to ultraviolet wavelengths. Astronauts also replaced power supplies, computers, and other hardware needed to keep the observatory running.
“It’s like a new telescope,” Christian says. “It’s like it’s only five years old in some respects.”
[Editor's note: This article has been updated to clarify which University of Maryland campus historian Joseph Tatarewicz is affiliated with.]