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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 23: Seeing the invisible
a.k.a. Dr. Joe Liske.

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When you listen to your
favourite piece of music,

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your ears pick up on the very
wide range of frequencies,

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from the deepest rumblings of the bass
to the very highest pitched vibrations.

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Now imagine your ears were only sensitive
to a very limited range of frequencies.

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You'd miss out on
most of the good stuff!

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But that's essentially that
situation that astronomers are in.

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Our eyes are only sensitive to a very narrow
range of light frequencies: visible light.

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But we are completely blind to all
other forms of electromagnetic radiation.

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However, there are many objects in
the Universe that do emit radiation

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at other parts of the
electromagnetic spectrum.

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For example, in the 1930s
it was discovered by accident

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that there are radio waves
coming from the depths of space.

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Some of these waves have the same
frequency as your favourite radio station,

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but they are much weaker and, of
course, there's nothing to listen to.

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In order to "tune in"
to the radio Universe,

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you need some sort of
receiver: a radio telescope.

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Now for all but the longest wavelengths,
a radio telescope is just a dish,

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much like the main mirror
of an optical telescope.

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But because radio waves are so
much longer than visible light-waves,

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the surface of the dish doesn't have to be
nearly as smooth as the surface of a mirror.

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And that's the reason why it's so much
easier to build a large radio telescope

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than it is to build a
large optical telescope.

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Also, at radio wavelengths, it is
much easier to do interferometry.

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That is, to increase the level of
detail that can be seen

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by combining the light
from two separate telescopes,

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as if they were part
of a single, giant dish.

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The Very Large Array in
New Mexico, for example,

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consists of 27 separate antennas,
each measuring 25 metres across.

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Now each antenna can be
moved around individually,

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and in its most extended configuration
the virtual dish mimicked by the array

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measures 36 kilometres across.

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So what does the Universe
look like in the radio?

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Well, for a start our Sun shines
very brightly at radio wavelengths.

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So does the centre of
our Milky Way galaxy.

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But there's more.

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Pulsars are very dense stellar corpses

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that emit radio waves only
into a very narrow beam.

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In addition, they rotate at speeds of up
to several hundred revolutions per second.

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So in effect, a pulsar looks
like a rotating radio lighthouse.

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And what we see from them is a very regular
and fast sequence of very short radio pulses.

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Hence the name.

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The radio source known as
Cassiopeia A is in fact the remnant

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of a supernova that
exploded in 17th century.

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Centaurus A, Cygnus A and
Virgo A are all giant galaxies

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that pour out huge
amount of radio waves.

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Each galaxy is powered by a
massive black hole at its centre.

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Some of these radio galaxies
and quasars are so powerful

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that their signals can still be detected
from a distance of 10 billion light-years.

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And then there's the faint,
relatively short-wavelength radio hiss

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that fills the entire Universe.

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This is known as the
cosmic microwave background

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and it is the echo of the Big Bang.

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The very afterglow of the hot
beginnings of the Universe.

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Each and every part of the
spectrum has its own story to tell.

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At millimetre and
sub-millimetre wavelengths,

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astronomers study the formation
of galaxies in the early Universe

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and the origin of stars and
planets in our own Milky Way.

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But most of this radiation is blocked
by water vapour in our atmosphere.

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To observe it, you
need to go high and dry.

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To Llano de Chajnantor, for example.

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At five kilometres above sea level, this
surrealistic plateau in northern Chile

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is the construction site of ALMA:
the Atacama Large Millimetre Array.

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When completed in 2014, ALMA will be the
largest astronomical observatory ever built.

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64 antennas, each weighing 100
tonnes, will work in unison.

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Giant trucks will spread them out
over an area as large as London

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to increase the detail of the
image, or bring them close together

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to provide a wider view.

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Each move will be made
with millimetre precision.

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Many objects in the Universe
also glow in the infrared.

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Discovered by William
Herschel, infrared radiation

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is often also called "heat radiation"

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because it is emitted by all relatively
warm objects, including humans.

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You may be more familiar with
infrared radiation than you think.

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Because on Earth, this kind of radiation

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is used by night vision
goggles and cameras.

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But to detect the faint
infrared glow from distant objects,

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astronomers need very
sensitive detectors,

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cooled down to just a few
degrees above absolute zero

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in order to suppress
their own heat radiation.

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Today, most big optical telescopes are
also equipped with infrared cameras.

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They allow you to see right
through a cosmic dust cloud,

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revealing the newborn stars inside,

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something that just cannot
be seen in the optical.

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For example, take this optical image
of the famous stellar nursery in Orion.

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But look how different it is when seen
through the eyes of an infrared camera.

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Been able to seeing the infrared is also very
helpful when studying the most distant galaxies.

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The newborn stars in a young galaxy
shine very brightly in the ultraviolet.

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But then this ultraviolet light
has to travel for billions of years

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across the expanding Universe.

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The expansion stretches the light-waves,
so that when they are received by us

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they've been shifted all the
way into the near infrared.

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This stylish instrument is the
MAGIC telescope on La Palma.

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It searches the sky
for cosmic gamma rays,

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the most energetic form
of radiation in nature.

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Lucky for us, the lethal gamma rays
are blocked by the Earth's atmosphere.

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But they do leave behind
footprints for astronomers to study.

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After heating the atmosphere, they
produce cascades of energetic particles.

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These, in turn, cause a faint
glow that MAGIC can see.

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And here is the Pierre Auger
Observatory in Argentina.

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It doesn't even look like a telescope.

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Pierre Auger consists of 1,600 detectors,
spread over 3,000 square kilometres.

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They catch the particle
fallout of cosmic rays

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from distant supernovas and black holes.

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And what about neutrino detectors?

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Built in deep mines or beneath the surface
of the ocean, or in the Antarctic ice.

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Could you call those telescopes?

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Well, why not?

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After all they do observe the Universe,

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even if they don't capture data
from the electromagnetic spectrum.

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Neutrinos are elusive particles that are
produced in the Sun and supernova explosions.

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They were even produced
in the Big Bang itself.

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Unlike other elementary particles,
neutrinos can pass through regular matter,

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travel near the speed of light
and have no electric charge.

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Although these particles may be
difficult to study, they are plentiful.

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Each second more than 50 trillion electron
neutrinos from the Sun pass through you.

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Finally, astronomers and
physicists have joined forces

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to build gravitational wave detectors.

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These "telescopes" do not observe
radiation or catch particles.

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Instead they measure tiny ripples
in the very structure of space-time,

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a concept predicted by Albert
Einstein's theory of relativity.

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With a stunning variety of
instruments, astronomers have opened up

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the full spectrum of
electromagnetic radiation,

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and have even ventured beyond.

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But some observations simply
can't be done from the ground.

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The answer?
Space telescopes.

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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.