The drive to map the sky is as old as civilization itself. The Great Pyramids in Egypt point straight at specific stars. The ancient stone configuration Stonehenge in Britain
is arranged to track the progress of the sun toward its northernmost
point in the sky. The first astronomical observatories date back as
early as the third century in the Middle East; at that time, astronomy was mixed up with astrology,
and sky-watchers used cosmic measurements to predict the future. Since
Islamic law forbids such superstition, many of the earliest astronomers
were executed for heresy.
But during the Renaissance period in Europe,
astronomy's ties to astrology were broken and it became a real science.
In the late 16th century, Hans Lippershey, an eyeglass-maker in
Holland, applied for the first telescope patent, claiming invention of a
device that made distant objects on Earth appear closer. Soon after, Galileo Galilei in Italy turned his own telescope to the sky for the first time and saw incredible sights, like craters on the moon and four bodies orbiting Jupiter.
His discoveries tended to fly in the face of religious dogma, though,
and he had to retract much of what he said. Still, the telescope went on
to completely change our understanding of the world beyond our planet.
What Galileo viewed
through his "far looker" was a blurry mess compared to what we can see
today. Not long after Galileo saw the moon up close, inventors like
Johannes Kepler, Isaac Newton and N. Cassegrain made a succession of
major innovations in telescope design. Since then, developments in our
understanding of astrophysics, along with technological advancements in
optics, engineering and rocket science have led to amazingly clear,
distant views of our galaxy and far, far beyond. Current telescopes can even see matter disappear into a black hole.
And the telescope race is just heating up.
In this article,
we'll look at 10 of the most amazing telescopes of our time, including
several that are still on the drawing board and promise to reveal images
of the Big Bang itself. Many of these new telescopes are funded
partially by private donors. We'll begin with some of the greatest
ground-based telescope systems in use today. Because they have to be
able to see through the Earth's atmosphere, these telescopes are truly
massive.
Technically speaking,
the South African Large Telescope, or SALT, is the biggest telescope in
the Southern Hemisphere. But when it comes to telescopes, how big is
"big?"
In an optical telescope, performance depends primarily on two characteristics: the ability to collect light
bouncing off objects and the ability to focus that light to produce a
clear image of those objects. The ability to collect light is directly
related to aperture size, or the area available to capture light. In the huge telescopes
of modern astronomy, one or more mirrors serve to collect light. The
size of the mirror is the single most important determinant in how far a
telescope can see, since the farther away an object is, the fainter the
light bouncing off it.
It's mirror size that makes the Southern African Large Telescope (SALT), located just outside Sutherland, South Africa,
stand out among the most amazing telescopes in the world. With an
11.1-meter (36.6-ft) aperture, SALT can see distant galaxies and quasars
that are one billion times fainter than what can be seen with the human
eye [source: GTC].
No one can manufacture a single mirror of that size, which is about the
height of a three-story building, so SALT uses a collection of
hexagonal mirrors pieced together into one perfectly smooth mirror. A
single imperfection would distort the image it captures.
If we could see a
candle flame on the moon with the naked eye, we'd have the optical
acuity of SALT. However, while SALT comes in first with its 11-meter
aperture, part of the telescope design blocks the edges of the mirror.
Its actual aperture is more like 9.2 meters (30.18 ft) [source: GTC]. The Keck telescope system in Hawaii has a larger actual aperture, which makes it the second largest telescope system in the world.
At an altitude of 14,000 ft (4,267.2 meters), at the top of Hawaii's Mauna Kea peak, two massive telescopes
scan the universe for answers to some big questions -- how old is the
universe, and how quickly is it expanding? Each 300-ton, 8-story tall
telescope has an actual aperture of 10 meters (33 ft) and can collect
both visible and infrared light.
The massive mirrors
that collect and focus light are, like SALT's mirror, an array of
smaller mirrors arranged on a perfectly formed curve. The telescopes
have inner cooling systems to protect against the flexing that can come
with heat exposure. But one of the greatest parts of the system is a
tiny mirror that's actually supposed to flex. Even on Mauna Kea, Keck
has to deal with the distortion caused by Earth's
gaseous atmosphere, which is the greatest enemy to ground-based
telescopes. A 6-inch (15-cm) mirror in each telescope deforms its shape
670 times per second to make up for the effects of Earth's atmosphere on
incoming light [source: SALT].
The result is a pair
of telescopes that can see the past. Keck can pick up light that has
been traveling for billions of years. By the time this faint light hits
Keck's mirrors, the event that caused it is long gone. Keck is helping
astronomers determine the age of the universe and its expansion rate as
well as allowing them to watch the birth of stars in other galaxies.
If Keck can see back
in time, imagine what the biggest telescope in the world, the Great
Canary Telescope, can pick up with its chart-topping aperture.
The Great Canary
Telescope (GCT), situated on a mountain on La Palma in the Great Canary
Islands, cost $180 million to build. It claims the title of the biggest
telescope in the world, with a light-collecting area 10.4 meters (34.3 ft) across.
The telescope gathers
both visible and infrared light with a mirror made up of 36 smaller
mirrors. The entire 10.4-meter aperture is used at all times, making it
one of the greatest cosmic observers in the world. Like Keck, the GCT
uses adaptive optics to correct for the distortion caused when light
passes through Earth's atmosphere. In the Great Canary device, there are
several deforming mirrors, and each changes shape more than one
thousand times per second [source: GTC].
With its optical systems, the Great Canary Telescope can capture distant galaxies, black holes, and planets that orbit other stars besides the sun. It can capture light so old that it shows the birth of galaxies in the earliest days of the universe.
As large as a single
telescope's aperture can get, none can compare to the power of several
massive telescopes working together. While the light-collecting ability
of one 8.2-meter (26.9-ft) telescope might fall short of the incredible
Great Canary, the capacity of several of those telescopes working in
tandem leaves the GTC in the dust. That's where the Very Large Telescope
comes in.
Image Credit: Marco Simoni/The Image Bank/Getty Images
7. Very Large Telescope
Imagine a car on the moon with its headlights on. If you could look up at the moon and see each of the headlights as a distinct point of light, you'd have the observational power of the Very Large Telescope (VLT).
The VLT is actually an array of telescopes. In an array, several telescopes work together as a single unit, effectively creating one massive device. Radio telescopes -- which pick up radio waves instead of light waves -- are often used in arrays, like the Very Large Array in New Mexico, which was featured in the movie "Contact," and the Very Large Baseline Array, which stretches across the United States, from Puerto Rico to Hawaii.
The VLT is an array
of optical telescopes. It consists of four 8.2-meter (26.9-ft)
telescopes, each of which is a large telescope in its own right. One of
those telescopes, which can operate individually, too, can pick up light
4 billion times fainter than what we can see with our eyes -- that's
four times fainter than what SALT can see. There are also four smaller
telescopes that act as backups to boost the system.
The VLT can join up
to three of the huge telescopes into a single unit, using underground
mirrors to combine light from the individual telescopes into a unified
beam. The result is a telescope system that can see objects at 25 times
the resolution of each telescope on its own. The ultimate goal is to be
able to join together all four large telescopes into an array with the
light-collecting power of a single 50-meter (165-ft) telescope.
Another take on the array approach is the type of bimirror system used in the Large Binocular Telescope, possibly the most powerful telescope in the world.
Image Credit: Joe McNally/Getty Images
6. Large Binocular Telescope
A massive, two-part telescope called the Large Binocular Telescope (LBT) has already achieved first light -- the first image collected by a new telescope -- on a mountain in Arizona.
The binocular system uses two mirrors, each one with an aperture of 8.4
meters (27.56 ft). Unlike the duo or trio of 8.2-meter (26.9-ft)
mirrors at work in the Very Large Telescope, LBT has both mirrors
mounted on the same telescope. It's not an array -- it's a single,
massive unit with two huge, light-collecting mirrors. The system collects as much light as a telescope with a single 11.8-meter (38.8-ft) aperture [source: Popular Mechanics].
While it's already
operational, LBT is still getting up to speed. Billed by many as the
most powerful telescope in the world because of its effective aperture,
the system uses an innovative honeycomb structure for its huge mirrors
instead of a solid surface [source: Popular Mechanics].
The mirrors have a smooth front and an open honeycomb matrix in back,
making them much lighter than other mirrors and less prone to
gravitational distortion.
When it's fully operational (projected by 2010) astronomers expect LBT to see planets circling stars well outside our own galaxy with 10 times the resolution of Hubble Space Telescope,
aiding in the discovery of planets. They also believe it will capture
the first clear images of the types of space dust and gas pockets that
can develop into new galaxies.
All of the superlative ground-based telescopes have high-tech adaptive optics systems to correct for the effect of Earth's
atmosphere. There is really only one way to improve such systems: avoid
the atmosphere entirely. Space-based telescopes are a prime example of
combining technologies to achieve amazing results.
Take Hubble, for instance...
French inventor N. Cassegrain might be stunned to know his 1672 reflecting-telescope design, which was criticized by Newton at the time, is orbiting Earth in a satellite telescope called Hubble [source: Cartage].
No matter how big
ground-based telescopes get, they will always face the issue of
distortion caused by Earth's atmosphere. A smaller telescope deposited
in space, beyond Earth's atmosphere, can avoid the issue entirely. The
Hubble Space Telescope combines astronomy with rocket science and operates in Earth's orbit.
With an aperture of
2.4 meters (94.5 inches), Hubble is much smaller than state-of-the-art
ground telescopes, but its resolution is comparable or better, since the
light it collects has travelled only through the relative vacuum of space [source: Hubblesite.org].
Hubble captures faint light coming in from billions of light years from
Earth, which means it can see events that occurred billions of years
ago. Hubble helped scientists confirm that dark matter exists and narrow down the age of the universe to 13 or 14 billion years [source: Hubblesite.org].
Hubble captures
incredible images of the universe, but it's not the best space telescope
out there. The Chandra X-ray Observatory tops Hubble in revealing the
hidden world.
Chandra, the most high-tech X-raytelescope in the world, is so sensitive it can capture images of particles as they disappear into a black hole deep in outer space.
X-ray telescopes rely on higher-energy phenomena than light
telescopes. Chandra records images of the universe by analyzing energy
fluctuations on the level of X-rays, using a barrel-shaped series of
mirrors that make up a total aperture of 2.7 meters (9 ft) [source: Harvard]. Because the images are based on much higher-frequency waves of energy, they're clearer than Hubble's, and Chandra is a more sensitive instrument -- 25 times more sensitive than any other X-ray telescope [source: Harvard]. It also orbits Earth 200 times farther out than Hubble, so it's able to see deeper into space, peering out about 10 billion light years from Earth.
Chandra X-ray observatory has recorded crystal clear images of supernova remnants, quasars, exploding stars,
black holes, nebulae and dark matter, among other phenomena. Scientists
believe that Chandra will make startling contributions to our
understanding of the origins of life.
Chandra is certainly
not the last word in space telescopes. The Next Generation Space
Telescope is already in development. It will orbit the sun, not the Earth, and it could be launched by 2013 [source: FirstScience]. And like the space telescopes, ground-based devices are looking at a next generation, too.
The current
state-of-the-art instruments are in the 8-to-10-meter
(26.25-to-32.81-ft) aperture class. The next wave of telescopes will
squash that. The race is on to build the biggest telescope ever, and the
final three telescopes on our list are top contenders.
Much like the Large Binocular Telescope,
the Giant Magellan Telescopes uses several mirrors in the same device.
But instead of two 8.4-meter (27.56-ft) mirrors, Magellan has seven.
It's a $500 million project funded by several universities in the United States and Australia,
along with two U.S. research institutes. Its seven mirrors, arranged
with six segments surrounding a single central mirror, combine to create
a telescope with an approximate 24-meter (80-foot) primary mirror.
Based in Las Campanas, Chile,
the telescope has an adaptive optics system that can cancel out
atmospheric distortion to the point of producing images with 10 times Hubble's resolution [source: Wired].
Projected for completion by 2016, astronomers expect Magellan to
contribute to our understanding of the origins of life (one of the main
themes in modern astronomy) by picking up light that began its journey
billions of years ago.
While a 24-meter
(78.74-ft) aperture dwarfs the current largest Great Canary Telescope,
the next telescope on the list takes it up another notch. And it has the
price tag to prove it.
The name says it all. The Thirty Meter Telescope's massive primary mirror has 492 segments, all perfectly aligned to form a 30-meter (98-foot) light-collecting
surface. Each segment will be continuously computer-adjusted to
maintain the correct alignment to prevent any image distortion. Its
adaptive optics correct not only for atmospheric distortion but also for
ground winds that can alter observational accuracy.
The telescope will cost about $780 million and is funded in part by Intel co-founder Gordon Moore [source: RedOrbit]. It's expected to have 12 times the resolution of Hubble Space Telescope.
With a $200 million Moore Foundation grant, the Thirty Meter Telescope
is the closest of the next-generation devices to full funding. The
telescope could be under construction as early as 2009 and ready for
first light by 2016.
The Thirty Meter Telescope will be eight times more powerful than any current ground-based system [source: Discovery News]. But of the three next-generation ground-based telescopes on the list, none is as ambitious as our final entry. Europe is aiming to create a telescope that wipes out the competition.
At a cost of $1.17 billion, the European Extremely Large Telescope (ELT) is aiming high. The Chile-based
project, funded by a consortium of European Union countries, is
building a telescope with a 42-meter (138-ft) mirror. The original
design called for a 100-meter (330-ft) mirror but was downsized for
practical reasons.
Still, 42 meters is
nothing to sneeze at. This new class of telescope -- the 30-to-50-meter
class -- is only possible because engineers have come up with new ways
to build mirrors. The number of segments they can piece together into a
perfect surface has grown from the dozens to the hundreds, meaning the
possibilities of what these new telescopes can see is nearly endless.
As for the ELT,
astronomers are predicting the discovery of new planets and entire
planetary systems, as well as revealing the events that gave birth to
the universe. As early as 2018, the 21-story-tall telescope should add
dramatically to our knowledge across the field of astrophysics,
providing insight into dark matter and dark energy, the space-time continuum and the inner workings of super-massive black holes.
With both private and public sources pumping hundreds of millions of dollars
into telescopes, our ability to see into the farthest corners of the
universe -- and into the farthest corners of time -- appears to be
limited only by how quickly we can build bigger instruments. No one
knows just what we'll see when the next-generation ground- and
space-based telescopes start delivering their images.
For more information
on telescopes, including upcoming projects and details on how these and
other telescopes work, look at the links on the next page.
Image Credit: NASA via Getty Images
Tidak ada komentar:
Posting Komentar
Silahkan anda berkomentar...asal tetap dalam koridor yang santun