[Music plays]
(Narrator) When the early astronomers looked at the heavens
they regarded the Sun as a unique object
quite distinct from other celestial bodies.
Modern astronomers know that the Sun is actually a star
typical of countless millions in our galaxy
yet for all that the Sun still has a special place.
It is the only star close enough to be seen in any detail.
It is our star.
At Culgoora 650 kilometres northwest of Sydney
CSIRO scientists are studying the Sun and its atmosphere
using both radio and optical instruments.
The main optical telescope is mounted on a tower 15 metres high.
This minimises the image-spoiling effects of turbulent air currents
which are worse near the ground.
It's a 30 centimetre high resolution telescope
designed and built by CSIRO's Division of Applied Physics.
It can photograph details of the Sun's surface as small as 330 kilometres.
An electronic eye continuously monitors the sharpness of the solar
image and operates the camera whenever the image is right.
When the Sun is photographed in ordinary white light we obtain
an image of the photosphere, the visible disk of the Sun
which emits most of the light and heat we receive on Earth.
The dark patches known as sunspots
are the sites of intense magnetic fields.
Away from the sunspots the photosphere
has a mottled texture called granulation.
Each granule is the top of a convection current
which carries energy from the nuclear furnaces of the Sun's interior
to the visible surface. The Sun emits light over a range of wavelengths.
By using a special computer controlled filter
we can tune in to a specific wavelength and block out all others.
If we tune in to the H alpha line of hydrogen we see a previously
invisible region of the Sun's atmosphere, the chromosphere.
The chromosphere which lies directly above the photosphere
is a turbulent layer of great beauty and complexity.
By carefully tuning away from the centre of the H-alpha line
we can photograph other levels within the chromosphere.
These photographs are the starting point for investigating
the physical processes in the Sun's atmosphere.
A single photograph may require weeks of careful study
before all the scientific information can be extracted.
The bright patches in this series of photographs
are from a large flare. Flares are vast explosions in the Sun's
atmosphere thought to be caused by sudden changes in the
magnetic fields of nearby sunspots.
In a very large flare the amount of energy released is enormous,
something like the energy of 20,000,000 hydrogen bombs.
During these events the emission of X-rays and radio waves
is increased enormously and charged particles are accelerated
to cosmic ray energies and hurled out into space in vast amounts.
These explosions of the Sun affect our earthly
environment in several ways. They produce spectacular auroral displays.
They cause magnetic storms and interfere
with shortwave radio communication.
At Culgoora the Ionospheric Prediction Service
of the Department of Science and Technology uses an optical flare
patrol telescope as well as the unique data from CSIRO's radio
instruments to keep a daily watch on the Sun for flare activity.
This is one of several observatories around the world which
together maintain a 24 hour vigil on the Sun.
The Ionospheric Prediction Service Warning Centre in Sydney receives data
from Culgoora and other local observatories.
It also receives and exchanges data
with warning centres all over the world.
As soon as a significant chain of solar events is observed
advance warnings of possible terrestrial effects
are issued by the centre to many sections of the
community, industry, transport, defence, communications.
During a total eclipse the Sun becomes completely masked by the moon.
When the photosphere is obscured
we can see the vast outer atmosphere of the Sun.
This is the corona, a million times fainter than the photosphere.
The corona extends its tenuous arms into the near
vacuum of interplanetary space enveloping the Earth
in the so-called solar wind. To learn more about the corona we must turn our
attention to the radio waves it emits.
In the years after World War II radio astronomers
from CSIRO's Division of Radio Physics tuned into
radio waves from the corona and deduced its temperature.
Now at Culgoora the radio astronomers are continuing to tune in
to the Sun but with greatly improved radio receivers.
The radioheliograph, a unique instrument which came
into operation in 1967.
The radioheliograph is a giant ring of 96 aerials each 13.5 metres across
equally spaced around the edge of a circle three kilometres in diameter.
It was first designed to operate at one frequency
but now operates at four frequencies.
Each of these aerials is automatically steered to follow the Sun.
We have speeded up their movement here by about 50 times.
The radio signals received by each aerial
are amplified and carried along a network of overhead
lines to the central observatory.
(Man) What logical unit today Bob?
(Bob) Number one.
(Narrator) Here the signals are fed into a complex
of electronic circuits and computers which
synthesise them into pictures on a television tube
at a rate of one every second.
The inner circle represents the disk of the Sun.
The signals from the radioheliograph are recorded
on magnetic tape for later analysis.
In this major disturbance a band of bright radio emission is stretching
halfway around the Sun. This was caused by a huge
shockwave which arose in a gigantic explosion
on the hidden side of the Sun.
Sometimes enormous quantities of coronal gas are ejected from the Sun.
The following sequence speeded up many times
shows a giant blob of gas moving outwards at
300 kilometres a second.
It travelled 3,000,000 kilometres from the Sun before fading from view.
The pictures from the radioheliograph
are distributed all around the world for even today
no other country has equivalent facilities.
The information recorded on tape can be processed by the computer
to produce contour maps of radio emission
at the different frequencies recorded by the radioheliograph.
A three dimensional picture of a particular
radio source can then be built up.
This one shows how different frequencies come from
different positions in the corona.
As well as the 96 aerials of the radioheliograph
there are a variety of other aerials at Culgoora
which pickup radio signals from the Sun at particular frequencies.
The various signals are sorted out by a spectrograph
to produce a continuous radio spectrum
of the Sun showing the component wavelengths.
The radio emissions from the Sun are extraordinarily complex
but can be reduced to a small number of characteristic spectral types.
These records are carefully analysed and different types
of solar events can be identified.
Another type of spectrographic instrument records not the
intensity of the radio bursts but their degree of polarisation.
These records reveal a lot of information
about magnetic fields in the corona.
At Culgoora there is another extremely sensitive
spectrograph shielded by a fine copper mesh.
It reveals radio emissions too weak to be seen by the other instruments.
CSIRO's research at Culgoora is making a major
contribution to a worldwide study of the Sun.
All this is helping us to understand the subtle and complex ways in which
the activity of the Sun influences our environment on Earth.
As well as ground-based observations
we now have observations from satellites.
Orbiting high above the obscuring effects of the Earth's atmosphere
man's eyes in space are able to see the Sun
with a new and exciting clarity.
To the physicist the Sun is a unique laboratory in space
where he can study the interaction of hot ionised gases
and strong magnetic fields.
The knowledge gained may one day make it possible for man to duplicate the
Sun's thermonuclear fires here on Earth in a strictly controllable way.
Continuing research on the Sun in both the radio and optical regions
of the spectrum is an integral part of modern physics,
astronomy and the study of the Earth's environment in space.