around the world are competing to build the world's most powerful
telescope. Their designs range from a supersized Hubble Space Telescope
to the world's biggest pair of binoculars - and a telescope as big
as a football pitch.
by Nigel Henbest
High above the Earth, a gargantuan telescope peers into space.
It dwarfs the Hubble Telescope, the twentieth-century's greatest
scientific instrument. With a mirror half the size of a tennis court,
the Next Generation Space Telescope will reveal the edges of the
The Next Generation Space Telescope is already on the drawing board.
Within 10 years, this ultimate telescope will be flying in space.
Instead of orbiting the Earth, the Next Generation Space Telescope
will follow its own orbit around the Sun. But its designers will
place it at a special balance point, outside Earth's own orbit.
At this location, the so-called Lagrangian-2 point, our planet's
gravity still ensnares the telescope, so it travels round the Sun
always a million miles from the Earth.
Huge solar panels will provide the telescope with power, and -
just as important - shield it from the Sun's heat. Cooled down to
the temperature of deep space, the Next Generation Space Telescope
can observe faint heat signals from the farthest reaches of the
Universe. It will peer beyond where even Hubble can see, to the
very edges of the observable Universe.
Because light takes billions of years to travel this far, the Next
Generation Space Telescope will be seeing these distant regions
as they were billions of years ago - just after the Big Bang in
which everything began.
This ultimate telescope combines the clear views that Hubble enjoys
with the mammoth size of the biggest telescopes currently being
built on the ground.
In the dry deserts of Chile, astronomers are this year completing
the most powerful telescope ever constructed on Earth. The Very
Large Telescope in fact comprises four telescopes, on the peak of
a mountain that has been blasted flat to form a platform for the
cosmic quartet. Each of the telescopes has a mirror 8 metres (26
feet) across. Linked together, the four instruments will collect
as much light as a single telescope over 50 feet in size.
Three of the four telescopes are already working, and astronomers
have been astounded by the quality of their views of the cosmos
- of glowing nebulae, dying stars and distant galaxies.
Next Generation Space Telescope will travel round the sun
1 million miles from the Earth
To construct such a vast telescope, its builders have pushed engineering
to the limit. In particular, the telescope must tilt to turn to
different galaxies, giving gravity a purchase on its huge - but
thin - mirror. If gravity bends the mirror by an amount smaller
than the width of a human hair, the telescope's view of giant galaxies
is blurred to uselessness. So the designers have attached the back
of the mirror to hundreds of moving supports, computer-controlled
to push the mirror back into shape - a millionth of an inch at a
time - as the telescope tilts.
While telescopes in Chile are placed to view the southern sky,
the best place on Earth for observing the northern heavens is the
14,000-foot high peak of Mauna Kea, Hawaii. Here, astronomers have
constructed the world's biggest astronomical observatory. Put together,
the total area of the mirrors in these telescopes would outstrip
even the Very Large Telescope. But these instruments are competitors,
each seeking to be the most powerful telescope observing the northern
part of the sky.
M Keck Observatory
first Keck telescope has discovered tiny ice planets beyond
Gemini North is the latest, starting work this year. The surface
of its mirror is so smooth that if you enlarged it to the size of
the Earth, the largest bump would be only a foot high. Next door
is the Japanese telescope Subaru, with the biggest single mirror
in the world - almost 8.3 metres (27 feet) across. Like the Very
Large Telescope, it has hundreds of supports, actively pushing the
mirror into the precisely correct shape.
But the jewels in the crown of Mauna Kea are the pair of Keck Telescopes.
Each has a mirror 10 metres (33 feet) across. No-one could manufacture
a single piece of glass that size, so the Keck mirror is made of
36 pieces, each just six feet across, fitted together like bathroom
tiles. A perfect fit between the tiles is ensured by a computer-activated
system, pushing on the back of each segment to ensure the tiled
mirror forms a single perfectly smooth surface. To spread the forces
evenly, the support system is based on a design used to even out
the force of horses pulling a Wild West covered wagon!
The first Keck telescope has been observing for eight years, and
it has revolutionised astronomy, from discovering tiny ice planets
beyond Pluto, to tracking planets of other stars - and pinning down
the distances to the farthest known galaxies, over 10 billion light
Graham International Observatory
Large Binocular Telescope has giant mirrors made of glass
Texas has an even bigger panelled telescope, the Hobby-Eberly Telescope,
some 12 metres (almost 40 feet) in diameter. Its design has brought
it in at only one-tenth the cost of Keck, with the payoff that it
cannot focus quite as accurately. Its strength, instead, will come
from splitting up the light from distant objects in more detail
than any other telescope.
On Mount Graham, in Arizona, the world's 'biggest binoculars' are
about to peer at the sky. The Large Binocular Telescope has two
giant mirrors - each 8.4 metres (27 feet) across - mounted on the
same frame. But astronomers here have decided against the complication
of using hundreds of computer-controlled supports to keep the mirror
Instead, they've made the world's biggest glass honeycomb, with
its front curved to focus starlight. The empty honeycomb structure
behind keeps the mirror rigid enough to stay in shape as the telescope
tilts, without complicated support structures. At the same time,
it is much lighter in weight than a solid mirror of the same proportions.
These honeycomb mirrors are made in a giant furnace in a basement
in Tucson. Glass is melted in a mould that contains ceramic blocks
where the holes are required: when the mirror has cooled, the ceramic
will be washed out with a high-pressure hose to leave the empty
spaces in the honeycomb. Before that, the mould is heated to melt
the glass; the whole red-hot mass is then spun around hundreds of
times a minute, so the top surface naturally forms into a shallow
bowl shape - by a fortunate coincidence, just the right shape to
M Keck Observatory
distant galaxy as seen by the Keck telescope
These 'ten-metre' class telescopes are giving the Hubble Space
Telescope a good run for its money. Although Hubble has the sharpest
views of the distant Universe, it is puny compared to these giants:
its mirror is outranked by some 30 telescopes on the ground. Each
of the huge Keck Telescopes in Hawaii, for example, collects so
much light that it can "see" stars 10 times fainter than Hubble
can perceive. Astronomers routinely search out strange distant galaxies
with Hubble's sharp eye, then analyse their light with the vast
collecting power of Keck.
The Next Generation Space Telescope will combine Hubble's sharp
views with the power of today's large telescopes on Earth. And so,
some astronomers are moving on to dream up even bigger instruments
that could be built on terra firma. The most audacious plan of all
the OverWhelmingly Large Telescope.
The OverWhelmingly Large Telescope - OWL for short - would have
a mirror 100 metres across. That's as big as a radio telescope like
Jodrell Bank or the Green Bank radio dish in West Virginia. In everyday
terms, we're thinking not so much of a tennis court but of a football
The OWL concept has been hatched by astronomers from the European
Southern Observatory, which has built the Very Large Telescope in
Chile. Inspired by the segmented mirrors of Keck and the Hobby-Eberly
telescope in Texas, they propose fitting together some 1600 separate
hexagonal mirrors, to create a mirror surface 100 metres across.
It will be housed in a vast metal framework that can swivel to point
to any part of the sky.
If OWL is built, it will have the power to pick out individual
stars in galaxies halfway across the Universe, and to see planets
in orbit around other stars. It may take us on the final step to
answering the ultimate questions about the beginning and end of
the Universe, and the existence of life elsewhere.
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