[Beeping noise and static]
(Narrator) Astronomy is the oldest of the sciences.
Since the dawn of history the sun by day
and the myriad stars by night
have never ceased to fill man with wonderment and awe.
Space is populated by millions upon millions of stars
each like our own sun but incomparably more distant.
They are associated into huge groups
often visible as spectacular clusters and nebulae,
each a separate star system like the Milky Way to which we belong.
We know these things because astronomers
with their powerful telescopes can actually see and
photograph the light waves from far distant stars.
But the discovery that radio waves were also reaching us from outer space
has led to the building of completely new kinds of telescopes,
radio telescopes to track down where these radio
signals are coming from and what they mean
and so began the science of radio astronomy
using radio waves instead of light waves.
Light waves come in a variety of wavelengths.
White light is a mixture of wavelengths.
They can be seen as separate colours
when white light is passed through a prism.
The shortest wavelength we see as violet light
and the longest as deep red.
Radio waves are about a million times longer
and radio astronomy is concerned with those from about
one centimetre to 30 metres.
Radio telescopes are basically similar to optical telescopes.
Just as optical telescopes use a concave mirror
to collect the light waves and concentrate
them to give a visible image
so radio telescopes use a concave reflector of metal
or wire mesh to concentrate the radio beam
and pass it on to a suitable receiver.
Only the waves coming from the direction in which the
radio telescope is pointed are focused and recorded.
Those from other directions do not reach the receiver.
It can therefore be used to tell from which direction
the radio signals are coming.
By using this radio telescope the radio signals are collected,
passed to a special receiver and recorded on a moving paper strip.
The telescope scans the sky and if it points
near a star sending out radio waves such as the sun,
the signal increases
reaching a maximum when it points directly at the sun.
The larger the telescope the sharper and narrower the hump
and hence the more accurately we can fix the direction.
But as large telescopes are costly to build
various methods have been devised to give almost the same results
with smaller ones. A small radio telescope
gives a broad hump response.
When two or more spaced some distance apart are connected together
this response is broken up into a series of narrow ones
from which it is possible to fix the direction
of the source much more accurately.
This arrangement is called an interferometer
and one of the earliest was set up
in 1946 at the entrance to Sydney Harbour.
It appears to have only one aerial
but as the sun rose radio waves reached this aerial direct
and also after reflection from the sea.
This is equivalent to having two aerials and no sea
and so it behaved as an interferometer.
It recorded the signals from a strip of sky
narrower than the diameter of the sun.
In February 1946 strong signals were recorded
from somewhere within this band of the sun.
One of the largest sunspots ever seen was visible at this time.
Several days later the sun had rotated to a new position
and radio signals were coming from this direction.
To investigate this association of radio signals with sunspots
a special interferometer was constructed at
Potts Hill Reservoir near Sydney.
This one was for many years unique to Australia.
These 32 aerials each 6 feet in diameter
and mounted accurately in line
register signals from a strip of sky about one-tenth of the sun's diameter.
As the sun moves across the sky
the radio waves from each successive strip
of it are recorded in turn.
These are usually stronger from the rim of the sun
and the radio sun is larger than the visible disc
represented here by a coin.
Sometimes a pronounced hump on the chart
showed that very strong signals were coming
from one particularly active part of it.
There was usually a prominent sunspot
to be seen when this occurred.
To pinpoint exactly the positions of these active areas
this imposing array of 64 separate aerials
each 19 feet in diameter and arranged in the form of a cross
has recently been erected near Sydney.
It is known as a cross-grating interferometer.
Each aerial is mounted on its own polar axis
and all 64 can be moved in unison in small steps
so as to follow the sun across the sky.
One line of aerials responds to radio signals
from these narrow segments of the sky.
The second line at right angles
responds to signals from these segments.
By special methods of connection
only the radio waves from these small areas are recorded.
Each area is about 100th of the sun's disc.
As the sun moves across the sky it is scanned by one of these spots
and the radio waves recorded.
The aerial system is then changed so that the grid
of spots takes up a new position
scanning now an adjacent strip of the sun.
By repeating this process the whole face of the sun can be charted.
Radio pictures already made show that
although radio waves are coming from all parts of the sun
they are much more intense from certain localised areas
which we call radio spots.
Comparing this radio map with a photograph taken at the same time
it can be seen that the radio spots coincide with sunspots
when they are near the centre
but are otherwise displaced towards the rim of the sun.
This suggests that they are located in the sun's atmosphere
above the sunspots and this is definitely confirmed
by this radio spot shown right outside the visible disc,
obviously well up in the sun's corona.
These spots are up to 50,000 miles above the surface.
Radio astronomy shows that radio waves are
being generated continuously in the sun's corona
and from their intensity we know that
although the sun's surface is at a temperature of 6000 degrees centigrade
the outer corona must reach a temperature
of about a million degrees.
In addition, occasional but very intense bursts of radio light
are emitted from the sun. These last for only a few seconds or minutes
and again come from the general vicinity of sunspots.
To investigate these short period disturbances
a special telescope was built. It is, in effect,
a radiofrequency spectrograph.
Its three aerials are pointed at the sun
and then follow it across the sky from sunrise to sunset.
Signals from the sun are fed into receivers which tune rapidly
over a band of from one to seven metres then to a cathode ray tube.
An increase in signal causes the spot to jump upward.
When a disturbance lasts only a few seconds it is called a burst.
Bursts occur at random wavelengths
and are roughly analogous to a lightning flash.
Outbursts are more spectacular.
This record has been speeded up
to show that they slowly increase in wavelength.
Outbursts are quite possibly the result of explosions deep in the sun.
The increase in wavelength is attributed to a
disturbance travelling outward. Here it is again.
Their speed has been estimated to be about 500 miles per second.
Faster still are the high-speed bursts
changing much more rapidly in wavelength
and shot out at about 50,000 miles per second, one-third the speed of light.
Usually several high speed bursts precede an outburst.
Particles shot out from the sun during high-speed bursts
sometimes hit the earth
when they seem to be associated with cosmic ray effects.
They are followed a day or two later
by streams of slower moving particles from the outburst.
These are the ones which cause magnetic storms and auroral displays
and so radio astronomy gives us some
advance warning of when they're likely to occur.
The sun is not the only radio transmitter in the sky.
Jupiter, the largest of the planets, broadcasts radio waves strongly.
They sound rather like atmospherics from a distant thunderstorm.
The cause of the signals is obscure.
They come from the vicinity of spots quite possibly dust clouds
which are observed occasionally in certain parts of Jupiter's atmosphere.
But the really outstanding broadcasters
of the skies are the radio stars.
The first investigations in Australia were made at
Dover Heights near Sydney in 1946.
Strong radio waves were recorded from parts of the sky
as they rose above the sea. Often the signals
came from areas where there were no bright visible stars
and so the name radio star was coined
to describe something that emitted radio waves more strongly than light.
The Crab Nebula was the first visible object
to be identified as a radio star.
It is the remains of an exploding star first seen by Chinese
astronomers 900 years ago.
Another radio star in an apparently blank part of the
constellation Cygnus was not identified until special
photographs had been taken with the 200 inch telescope at Mount Palomar.
It turned out to be two great star systems
colliding with each other almost at the fringe of the visible universe.
One of the most powerful telescopes in the world
for studying radio stars is the Mills Cross.
Each arm is 1500 feet long
and contains 500 separate dipole aerials
working at a wavelength of 3.5 metres.
The Mills Cross has already charted over 1000 radio stars.
It works like this. One line of aerials
responds to signals from this narrow strip of sky
and the other to signals from this region.
When the signals from both are combined
the only signals recorded come from the part of the sky
where the beams overlap.
This is about three quarters of a degree across.
The beam can be moved to the north or south as
desired by connecting the separate aerials in different ways
hence it is possible for most parts of the sky
to pass through it once a day.
A second cross more than twice as long and working at a
longer wavelength, 15 metres, has now joined in the hunt.
The radio stars fall into two groups.
If we plot the brighter ones on a map of the skies
most of them fall in or near the Milky Way.
These include the Crab Nebula
and this bright patch in the constellation of Orion.
The faint radio stars however are located around us
in a more haphazard fashion.
These are other galaxies or systems of stars,
some enormously distant from us.
Some seen by large telescopes look like giant Catherine wheels.
These are the spiral nebulae, their long trailing arms
consisting of stars, clouds of dust and hydrogen gas
out of which new stars are born.
Astronomers have long suspected that our galaxy,
the Milky Way, might be a spiral nebula.
It is difficult to be sure about this by optical methods
because the hydrogen clouds are completely invisible
unless lit by a nearby bright star
and large dark clouds of dust in various directions
completely hide what lies beyond them.
Light waves cannot penetrate these clouds
but radio waves can and further,
the hydrogen clouds can easily be detected by radio methods
because they send out radio waves of one characteristic
wavelength near 21 centimetres.
This wavelength is not quite constant due to the rapid movement
of the clouds relative to the earth.
You have probably noticed that the whistle from a train
sounds higher in pitch as it approaches than when it is moving away.
[Train whistle]
In very much the same way radio whistles from hydrogen clouds
are shifted in wavelength, in this direction if they are approaching
and in the opposite direction if they are moving away.
From this change in wavelength the speed and distance of the clouds can
be estimated and charted.
Australian radio astronomers have thus mapped the
position of some of the hydrogen clouds.
Other clouds not visible from Sydney
have been plotted by European observers.
A definite spiral pattern is beginning to emerge.
By contrast this is the only part of our galaxy optical
astronomers have been able to explore even with the
largest telescopes. Radio astronomy is thus giving us for
the first time a more complete picture and confirms we
are in fact living in a spiral nebula.
Hydrogen signals have also been identified from the Clouds of Magellan
which are the nearest of the external star systems or galaxies to us.
By radio these clouds look much larger
showing that the hydrogen spreads out much further
than the visible stars.
Hydrogen signals are also being picked up from other
star systems which are very much more distant.
Perhaps every galaxy is enclosed in a large envelope of gas.
There are countless numbers of these star systems
scattered throughout space all apparently rushing away from us.
The faster, the further away they are.
Very large and powerful radio telescopes are needed to
study them in detail. One with an aerial 250 feet across
has just been completed at Manchester, England.
Plans are now being finalised for another giant instrument
soon to be built in Australia near Sydney.
It will have an aerial 200 feet in diameter.
Radio astronomy has made remarkable progress in the few years
since its birth in 1946 and Australia's contribution
has been quite a significant one.
Radio astronomy enables us to see some things in
a completely new light, to see others
that are not optically visible at all and to reach even further
out into space than optical astronomers can.
Radio astronomy is thus helping to uncover some of the fascinating
secrets of the heavens, how stars and galaxies are born,
live and die and whether the universe is really expanding
or not but it is still very much in its infancy.
The full story must be left for the future to fill in.