Hubble Space Telescope and Its Influence on Astronomy
Hubble Space Telescope and Its Influence on Astronomy
From the age of the universe to the existence of black holes and the discovery of new galaxies, the Hubble Space Telescope (HST) is providing a multitude of data for astronomers eager to understand the cosmos. While the telescope is providing images and data about deep-space objects, stellar systems, and other curiosities, it actually travels no farther than 380 miles (612 km) from Earth. A cooperative program of the European Space Agency and the National Aeronautics and Space Administration (NASA), the Hubble Space Telescope is an orbiting observatory, revolving around the Earth once every 93 minutes. It is able to collect data unavailable to Earth-based observatories, because the HST's location is unhampered by distortion from our planet's atmosphere. Since its 1990 deployment, the telescope has collected information and images that are helping astronomers generate a better picture of the universe and how it works.
The $1.5 billion Hubble Space Telescope was deployed into orbit by the space shuttle Discovery on April 25, 1990. The launch culminated two decades of work by researchers at NASA and other laboratories. Because the HST received its transportation into orbit via shuttle, it had to be lightweight and compact. The 13-ton [43 feet] HST is about the size of a railroad car (13.1 meters [43 feet] long and 4.3 meters [14 feet] in diameter at its widest point), considerably smaller than major Earth-based observatories, such as the 12-story Mount Palomar observatory in California. Its mirror is also much lighter than the traditional variety. By using a honeycomb design, engineers were able to eliminate two-thirds of the weight of a conventional mirror.
In addition, scientists had to design an intricate pointing system that would allow the solar-powered telescope to lock onto a target and maintain that lock even as the telescope circles the Earth at 8 kilometers per second (17,895 mph). The telescope accomplishes this feat through a complex of sensors and computer-controlled wheels. The Fine Guidance Sensors verify the telescope's target position 40 times a second, while the wheels correct for any deviation.
Protection of the HST from extreme heat change was another consideration. The HST circles the Earth every 93 minutes, going from the light side of Earth to the dark side—about a 120° difference in temperature—during every revolution. The solution was an exterior thermal blanket, which maintains a constant temperature for the telescope.
Despite all of the technology and abilities available aboard the HST, scientists, engineers, and computer programmers on Earth still are essential to the telescope's operation. Men and women at the Space Telescope Science Institute and Goddard Space Flight Center in Maryland carefully plan the telescope's operation down to the last detail, and radio instructions to the orbiting observatory. The telescope can then make observations in the visible, near-ultraviolet, and near-infrared spectra.
The HST follows the instructions, which may be to take a picture of or collect data on a distant star or galaxy. The pictures and data are translated into signals, radioed to Earth, then retranslated into pictures and data for use by astronomers and other scientists.
Throughout the telescope's tour of duty, astronauts have periodically visited the HST to upgrade its capabilities, perform tune-ups, and make repairs. The most well-publicized repair occurred after scientists and engineers discovered a flaw in the telescope's primary mirror, which blurred the HST's pictures. The solar panels also experienced problems when the telescope moved from the light to the dark side of Earth. The panels flexed enough to affect the accuracy of the pointing system. In 1993 astronauts aboard the space shuttle Endeavor replaced the solar panels and installed two devices with corrective optics.
The Hubble Space Telescope is named for American astronomer Edwin Powell Hubble (1889-1953), who discovered in 1929 that the universe is expanding. This idea formed the basis for the widely held Big Bang Theory, which states that a huge explosion created the universe, and the universe is even now continuing to expand out from the point of the explosion. Hubble also proved that galaxies exist beyond the Milky Way.
The data and images collected by the Hubble Space Telescope have yielded key evidence for a variety of scientific hypotheses, provided information that is helping to unlock some of the mysteries of the cosmos, and changed the way scientists and the public look at our universe.
For example, the HST has repeatedly provided views of previously unseen galaxies. In 1999 the HST yielded images of a spiral galaxy much like the Milky Way in size but 60 million light-years away. (One light year is the distance that light travels in a year, or approximately 6 trillion miles. [over 9 trillion km]) The spiral arms of the galaxy, dubbed NGC 4414 and located in the constellation Coma Berenices, are signs of ongoing star formation.
The telescope's data and images have also provided information about how quickly different types of galaxies formed following the Big Bang and about how rapidly the universe is expanding from that initial cosmic event. Wendy L. Freedman, head of the Hubble Space Telescope Key Project on the Extragalactic Distance Scale, and Allan R. Sandage of Carnegie Observatories, analyzed HST-collected data for Cepheid variable stars, including three dozen located in the spiral galaxy NGC 4603 in Centaurus, and put the expansion speed, known as the Hubble constant, at 58-70 kilometers per second per megaparsec.
While the HST was viewing yet another galaxy, the giant radio galaxy M87, astronomers observed subatomic particles appearing to move at six times the speed of light within a jet emanating from the galaxy's core. The movement was actually an optical illusion, called superluminal motion, produced because of the orientation of the jet to Earth. In reality, the particles likely move at a velocity slightly below the speed of light. As reported in the May 1999 issue of Astronomy, "According to John Biretta of the Space Telescope Science Institute, the discovery of superluminal speeds in M87 practically confirms the belief that radio galaxies, quasars and blazars are essentially the same, and differ only in orientation with respect to the observer."
Astronomers provided a glimpse back in time by producing an image called the Hubble Deep Field. The image is a melange of 342 separate exposures photographed by HST's Wide Field and Planetary Camera 2 during a 10-day period in 1995. Taken inside a small sliver of the universe near the handle of the Big Dipper (part of the constellation Ursa Major), the Hubble Deep Field image contained some 1,500 galaxies, most of which had never before been seen. In a Space Telescope Science Institute press release, institute director Robert Williams remarked, "We are clearly seeing some of the galaxies as they were more than 10 billion years ago, in the process of formation. As the images have come up on our screens, we have not been able to keep from wondering if we might somehow be seeing our own origins in all of this."
The data and images collected about galaxies are also providing distances between cosmic neighbors. With this information, astronomers are essentially working backward to try to determine how far the galaxies have traveled out from the origin of the Big Bang, and, thus, the age of the universe. In addition, the HST has detected gases and elements that give further credence to the Big Bang Theory.
In some of its most dramatic images, the HST offered views of the birth of stars. Images taken in 1999 depicted young stars surrounded by disks of dust and gas that astronomers believe may be the stuff of future planets. The images not only confirmed indirect evidence that the disks existed, but provided a level of detail previously unknown. Estimated to be from eight to 16 times the size of Neptune's orbit, the disks were located around newly forming stars 450 light years from Earth and in the constellation Taurus. Scientists believe the images might also provide clues to the formation of our solar system.
The Hubble took other revealing pictures of a star-forming nebula within the bright winter constellation of Orion. The images again showed embryonic stars surrounded by disks of potentially planet-forming dust. The Hubble took some of its most-used images of star birth in columns of dust and gas in the 2-million-year-old Eagle Nebula, which is located about 7,000 light years from Earth in the constellation Serpens. The images show so-called evaporating gaseous globules (EGGs) at the tips of the columns. Astronomers believe that the EGGs surround newly forming stars, created when the gas in the columns collapses on itself.
Closer to home, the HST has also provided the first-ever direct view of the surface of Pluto, unparalleled pictures of Jupiter as it was struck by pieces of the comet Shoemaker-Levy 9, images of Mars minerals containing signs that the Red Planet once held water, and additional evidence for a debris- and comet-filled ring that surrounds the solar system. The Hubble determined that the ring holds at least 100,000 comets.
Beyond the scientific impact, the Hubble Space Telescope is promoting education through the Space Telescope Science Institute. The institute merges images and data from the HST into online educational opportunities and other resources for students from elementary through high school levels.
LESLIE A. MERTZ
Barbree, Jay, and Martin Caidin. A Journey Through Time: Exploring the Universe With the Hubble Space Telescope. New York: Penguin Studio, 1995.
Fischer, Daniel, and Hilmar Duerbeck. Hubble Revisited: New Images From the Discovery Machine. New York: Copernicus, 1998.
Mitton, Jacqueline, and Stephen P. Maran. Gems of Hubble. New York: Cambridge University Press, 1996.
Petersen, Carolyn C., and John C. Brandt. Hubble Vision: Further Adventures With the Hubble Space Telescope. New York: Cambridge University Press, 1998.