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This is the Hubblecast.

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News and images from the
NASA / ESA Hubble Space Telescope.

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Travelling through time and space
with our host, Dr. J

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EPISODE 20: Technology to the rescue.
a.k.a. Dr. Joe Liske.

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Welcome to this third special
episode of the Hubblecast

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celebrating the International
Year of Astronomy in 2009.

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In the last episode we saw how
astronomers used bigger and bigger mirrors

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to see further than ever before.

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Today's topic is the advance of
technology through the 1970s and 80s

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that really revolutionised astronomy.

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Just as moderns car don't look
like a Model T Ford anymore,

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so are present day telescopes radically
different from their classic predecessors,

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like the five metre Hale telescope.

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For one thing, their
mounts are much smaller.

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The old style mount is an
equatorial one, where one of the axis

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is always mounted parallel
to the Earth's rotation axis.

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In order to keep track of the sky's
motion, the telescope simply has to rotate

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around this axis at the same
speed with which the Earth rotates.

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Easy, but space-hungry.

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The modern day altitude azimuth
mounts are much more compact.

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With a mount like that the telescope
is pointed much like a cannon.

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One simply chooses the bearing,
chooses the altitude and off you go.

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The problem is to keep
track of the sky's motion.

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The telescope pretty much has to rotate
around both axis and at varying speeds.

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Essentially this only became possible
once telescopes were computer controlled.

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A smaller mount is cheaper to build.

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Moreover, it fits into a smaller dome,

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which reduces the cost even further
and it improves the image quality.

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Take the twin Keck telescopes
on Hawaii for example.

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Although their 10 metre mirrors are twice
as large as the one of the Hale telescope,

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they nevertheless fit into smaller
domes than the one on Palomar Mountain.

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Telescope mirrors have evolved too.

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They used to be thick and heavy.
Now they're thin and lightweight.

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Mirror shells that can be many metres
wide are cast in giant, rotating ovens.

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And they are still less
than 20 centimetres thick.

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An intricate support structure prevents the
thin mirror from cracking under its own weight.

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Computer controlled pistons and actuators
also help to keep the mirror in perfect shape.

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This system is called active optics.

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The idea is to compensate and to correct
any deformation of the main mirror

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caused by gravity, the
wind or temperature changes.

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Now, a thin mirror
also weights much less.

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That means that its whole supporting
structure, including the mount,

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can also be a lot trimmer and lighter.

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And cheaper!

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Now, here is the 3.6 metre
New Technology Telescope,

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built by European
astronomers in the late 1980s.

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It served as a testbed for many of the
new technologies in telescope building.

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And even its enclosure has nothing in
common with traditional telescope domes.

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The new technology telescope
was a great success.

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It was time to break
the six metre barrier.

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Mauna Kea Observatory sits on
the highest point in the Pacific,

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4,200 metres above sea level.

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On the beaches of Hawaii, tourists
enjoy the sun and the surf.

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But high above them, astronomers
face chilling temperatures

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and altitude sickness in their quest to
unravel the mysteries of the Universe.

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The Keck Telescopes are among
the largest in the world.

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Their mirrors are 10 metres
across, and wafer-thin.

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Tiled like a bathroom floor, they
consist of 36 hexagonal segments,

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each controlled to nanometre precision.

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These are true giants, devoted
to observing the heavens.

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The cathedrals of science.

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Nightfall on Mauna Kea. The Keck
telescopes begin collecting photons

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from the far reaches of the cosmos.

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Their twin mirrors combining to be
effectively larger than all earlier telescopes.

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What will be tonight's catch?

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A pair of colliding galaxies,
billions of light-years away?

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A dying star, gasping its last
breath into a planetary nebula?

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Or maybe an extra-solar
planet that may harbour life?

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On Cerro Paranal in the Chilean Atacama
Desert, the driest place on Earth,

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we find by far the biggest
astronomy machine ever built:

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the European Very Large Telescope.

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The VLT is really
four telescopes in one.

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Each sporting an 8.2 metre mirror.

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Antu. Kueyen. Melipal. Yepun.

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Native mapuche names for the Sun, the
Moon, the Southern Cross and Venus.

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The huge mirrors were cast in
Germany, polished in France,

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shipped to Chile and then slowly
transported across the desert.

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At sunset, the telescope
enclosures opens up.

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Starlight rains down on the VLT mirrors.

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New discoveries are made.

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A laser pierces the night sky.

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It projects an artificial star into the
atmosphere, 90 kilometres above our heads.

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Wavefront sensors measure how the star's image
is distorted by the atmospheric turbulence.

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Then, fast computers tell a flexible
mirror how it has to deform itself

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in order to correct the distortion.

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In effect untwinlking the stars.

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This is called adaptive optics

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and it's the big magic trick
of present day astronomy.

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Without it, our view of the Universe
would look blurred by the atmosphere.

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But with it, our
images are razor-sharp.

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The other piece of optical
wizardry is known as interferometry.

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The idea is to take the light
from two separate telescopes

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and to bring it together
in a single point,

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while preserving the relative
shifts between the light-waves.

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If it is done precisely enough the
result is that the two telescopes

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act as if they were part
of a single, colossal mirror

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as large as the distance between them.

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In effect, interferometry gives
your telescope eagle-like vision.

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It allows smaller telescopes
to reveal a level of detail

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that would otherwise only be
visible with a much larger telescope.

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The twin Keck telescopes on Mauna Kea
regularly team up as an interferometer.

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In the case of the VLT, all four
telescopes can work together.

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In addition, several smaller auxiliary
telescopes con also join the ranks

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in order to sharpen
up the view even more.

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Other big telescopes can
be found all over the globe.

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Subaru and Gemini North on Mauna Kea.

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Gemini South and the
Magellan Telescopes in Chile.

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The Large Binocular
Telescope in Arizona.

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They are constructed at
the best available sites.

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High and dry, clear and dark.

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Their eyes are large as swimming pools.

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All kitted out with adaptive optics to
counteract the blurring effects of the atmosphere.

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And sometimes they can have the resolution of
a virtual behemoth, thanks to interferometry.

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Here's what they've shown us.

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Planets.

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Nebulae.

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The actual sizes, and
squashed shapes, of some stars.

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A cool planet orbiting a brown dwarf.

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And giant stars whirling around
the core of our Milky Way Galaxy,

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governed by the gravity of
a super-massive black hole.

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We've come quite a way
since Galileo's day.

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Thank you for joining me in this
third episode of the special series.

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Next time we will see how astronomers
have detected and measured light

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over the years, from hand
drawings to electronic detectors.

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This is Dr. J
signing off for the Hubblecast.

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Once again, nature has surprised us
beyond our wildest imagination...

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Hubblecast is produced
by ESA / Hubble

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at the European
Southern Observatory in Germany.

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The Hubble mission is a project
of international cooperation

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between NASA and
the European Space Agency.