The Hubble Space Telescope: 25 Years on the Cosmic Frontier


Hi everyone, I’m Darrell Heath with the UALR College of Arts, Letters, and Sciences; welcome to The Night Sky.

Almost from the moment of its invention in 1608 the telescope revolutionized our understanding of the universe and how we fit within it.   Using a crudely made telescope of wood and leather Galileo managed to bring two thousand years of dogma and human ego crashing to the ground by showing that Earth moved around the Sun along with all the other planets and not the other way around. His telescope used glass lenses to collect light and could only magnify objects 20 times; Sir Isaac Newton perfected the telescope a few years later with his own design that used a curved metal mirror to collect light rather than glass lenses, which were prone to color distortion of the image. Newton’s design also allowed for telescopes to be made bigger and cheaply. 400 years on the telescope still remains the primary tool astronomers use to unravel the secrets of the cosmos.   In pursuit of that quest to understand how the universe works astronomers have developed ever bigger and better telescopes and with improvements in telescope technology there have also come major leaps in our knowledge.

For the first 30 years of the 20th century the world’s largest telescope resided at the Mount Wilson Observatory in the San Gabriel Mountains just outside of Pasadena, California. It was a reflecting telescope similar to Newton’s basic design but rather than a metal mirror it used one made from two tons of melted and highly polished glass. Its aperture was 100 inches, a far cry from Galileo’s two-inch scope. And it was here at Mt. Wilson that not one, but two, revolutionary discoveries were about to be made.

In 1919 a young man named Edwin Hubble took a job at Mt. Wilson as an astronomer, in 1923 he became world famous by discovering that the Andromeda Nebula wasn’t just a cloud of gas within our own galaxy but, in fact, another island universe of stars like our own Milky Way, but much further away. In essence, Hubble discovered the universe; he demonstrated that galaxies existed outside our own and that they were distributed widely throughout the cosmos. Our universe became much bigger than we had ever thought possible.

His second discovery was even more astounding and Stephen Hawking has described it as “one of the great intellectual revolutions of the 20th century.”

Using Mt. Wilson’s 100 inch telescope Hubble discovered that galaxies are moving away from one another, in effect: the universe was expanding. This revelation was to lead to what we now call the “Big Bang” theory. Later discoveries were to confirm this finding of an expanding universe and it is now an accepted fact of modern cosmology.

Now, astronomers enjoy a breathable atmosphere just like the rest of us but what they don’t like is how it distorts their telescope images as well as blocks out certain wavelengths of light. The universe advertises its presence across the entire range of the electromagnetic spectrum, everything from high energy Gamma rays to low energy radio and microwaves. The human eye can only see a very narrow sliver of the EM spectrum, wavelengths that are only 380 to 760 nanometers long, which is what we know as “visible” light. Our atmosphere does a very good job of blocking out a large part of the spectrum from ever reaching the surface of the Earth. This makes us blind to much of what the universe has to offer and by the middle of the 20th century plans were being laid to place a telescope in space capable of seeing in various wavelengths, well above the blocking effects of our atmosphere.

In 1975 NASA teamed up with the European Space Agency to make what would become the Hubble Space Telescope a reality. By 1977 Congress had approved funding for the project and Hubble’s launch date was scheduled for October 1986. Unfortunately the tragedy of the Space Shuttle Challenger in January of that year resulted in a two-year delay for all NASA shuttle launches. Finally, on April 24th, 1990, the Hubble Space Telescope was launched into space aboard the Space Shuttle Discovery. But there were more setbacks to come.

The first images from Hubble were blurry and for a piece of high tech equipment that cost over $2.5 billion dollars this was an unacceptable problem. The fault was due to Hubble’s 94.5 inch curved mirror not being the correct shape as originally specified.   The flaw in the mirror was tiny; about 1/50th the thickness of a sheet of paper, but it was just enough to create the blurred images.   Engineers soon had a solution, a set of smaller mirrors would act as spectacles to correct the problem and would be installed as part of a space shuttle servicing mission. After a successful repair in December of 1993 the Hubble Space Telescope was back in business and ready to peer deep into the universe.

Hubble is specially equipped with a suite of five scientific instruments capable of looking at the universe in either ultraviolet, visible light, or infrared. Orbiting the Earth every 97 minutes the school bus-sized telescope is constantly gathering data in various wavelengths of light and sending it back to Earth. Astronomers routinely submit research proposals for various projects utilizing Hubble. Nearly 1,000 requests are sent in annually and around 200 are selected based upon which ones will make the best use of Hubble’s capabilities as well as whether or not the research being proposed has a high priority in astronomy.

Over the past 25 years the Hubble Space Telescope has made many astonishing discoveries about our universe but there are five in particular that stand out as being major scientific achievements.


One of the most important photographs ever taken is the Hubble Deep-Field, which allowed us to gaze across both space and time to when the universe was still in its infancy.   The first Hubble Deep-Field image was taken in 1995 when the telescope stared at a speck of seemingly empty space. The photo of this speck revealed some 3,000 individual galaxies going as far back in time as 10 billion years. It showed us that the earliest galaxies were small and irregular in shape and were probably the building blocks to the many large, grand spiral galaxies we see today.


While most extrasolar planets have been found using ground-based telescopes and various other space telescopes, Hubble has still made important contributions to their study. In 1994 Hubble showed that most of the infant stars within the Orion Nebula contain disks of gas and dust, the raw ingredients from which future planets will be made. In 2001 astronomers used Hubble to analyze the atmosphere of an alien world as it passed in front of its Sun-like star. This “proof of concept” study shows that we can use the technique to look at other alien planets to see if their atmospheres might contain signature gases that would betray the existence of living organisms.


Astronomers had long suspected that the bright and busy cores of some galaxies were host to supermassive black holes, compact gravity monsters that are millions or even billions of times more massive than our own Sun.   Hubble not only demonstrated that these black holes exist but that they are a common component of many galaxies ranging from normal spirals to misshapen and distorted colliding galaxies. More importantly, Hubble has shown that supermassive black holes, in addition to being common, are also intimately connected to galaxy formation and evolution.


The universe is filled with all kinds of exotic forms of matter and the most puzzling variety of all is one that we can’t even see: dark matter.   We’ve suspected the existence of this weird form of matter since the 1930’s but it has only been in the past few decades that scientists have become more certain of its reality.   While we have no real clue as to the nature of dark matter we can see it’s gravitational effects on more familiar varieties of matter; namely in how it keeps fast rotating galaxies from flying apart and how it also keeps fast moving galaxy clusters all held together.

While dark matter doesn’t emit or absorb light its mass can distort the fabric of space-time around it and can bend the light coming from more distant background objects. The phenomena is known as gravitational lensing and astronomers using Hubble and other space telescopes have used it to map out the distribution of dark matter within the universe.   These maps show that the cosmos is not only made up of 85% of a substance that we don’t even understand but that is also filled with spider web-like strands of the stuff, which seems to act as a scaffolding upon which the universe’s largest structures are built.


Edwin Hubble discovered that the universe is expanding and for most of the 20th century it was thought that all of the matter within it should be slowing the expansion rate down. But in 1998, two teams of scientists, working independently of each other, discovered that rather than slowing down, the universe’s expansion was accelerating.   Crucial to this research was the use of a specific kind of supernova event that astronomers often use as a cosmic yardstick when measuring distances across the universe. Only the Hubble Space Telescope could provide them with the level of precision needed to measure the most distant of these stellar explosions. We don’t yet know exactly what the energy source is for making the universe’s expansion rate accelerate and astronomers call it “dark energy” for that very reason.   Dark energy makes up 70% of the universe’s overall energy density and it may play a role in how the universe will meet its end. If the expansion rate continues or accelerates further then all of gravity’s work throughout the eons will come undone. Galaxy clusters will fall apart, the galaxies themselves will be torn asunder, and eventually even the molecules and atoms that make up visible matter will become shredded by the universe’s accelerated expansion.

Hubble has not only advanced our knowledge of the universe, it has also inspired works of art.   Choreographer Liz Lerman, recipient of a MacArthur “genius grant”, created a contemporary dance piece called “The Matter of Origins” which included images taken with the telescope. Artist Tim Otto Roth has created two art installation pieces inspired by Hubble’s discoveries. There is even a Hubble Cantata written by composer and visionary Paola Prestini in collaboration with astrophysicist Mario Livio. The work incorporates orchestral arrangements, vocalists, multimedia, and narration. The work serves to intermingle the fate of one young woman with the ultimate fate of the stars and a full-length version of the cantata is expected to debut in time for Hubble’s 25th anniversary.

But it is those stunning images from Hubble with which most of us are familiar.   Even without understanding the science that underpins them we are struck by their incredible beauty and we marvel at the awesome grandeur of a universe so vast in scale that we can scarcely grasp its true immensity. Hubble has become our own personal avatar in an attempt to understand the universe and our place within it, it is, in a very real sense, an extension of our own eyes into space and through which we look up at the night sky in awe and wonder.

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