http://www.skyandtelescope.com.au 11whom had worked on radar during the
war, found that by combining a signal
directly from an object with another
signal bounced off the surface of the sea,
they could ‘see’ much finer detail.
Back to April 1947, and the Sun
with its massive sunspot rose through
the beam of the antenna. At once,
radio static poured from the receiver.
Something on the Sun was making the
noise, and with their new and innovative
capacity for detail, the researchers could
identify the sunspot as the source.
Exciting in itself, the discovery was
a massive stimulus for the development
of what would soon be called ‘radio
astronomy’. It wasn’t long before similar
equipment was scanning the wider
universe and finding sources of radio
noise far away, including supernova
remnants such as the Crab Nebula. The
pioneers would no doubt be amazed
how far the technology has come since
then and how much we have learnt.
Less than a decade later, on April
5, 1955, the New York Times
devoted a column on its front
page to a discovery announced
at a meeting of the American
Astronomical Society. Two
astronomers from the Carnegie
Institute had detected radio
noise from Jupiter, short
bursts of static similar to the
interference on AM radio sets
from lightning strikes during
thunderstorms. The signals
had been found by chance and
several weeks of observations
were needed to determine that
Jupiter was the source. Clearly,
there was lightning to be found
on Jupiter too.■ DAVID ELLYARD is author of
Who Discovered What When
and Who Invented What When.Radio broadcasts from the Sun
‘Noisy’ sunspots were one of the drivers that led to radio astronomy.
A
stronomers know the universe
is ‘talking’ to us. Messages are
arriving all the time but in a
variety of languages, some of which we
have only recently learned to capture
and translate.
The most obvious (one-way)
communications arrive as visible light,
since we can detect those with our eyes.
We have been reading these signals for
millennia, and have ascertained an
immense amount about the universe
that enfolds us, especially once we
learned to amplify our powers of vision
using telescopes, cameras, spectroscopes
and other aids. In this way we have
come to appreciate the existence and
nature of planets, stars and galaxies and
the large structure of the universe.
But the cosmos has a lot more to
say in other languages. In April 1947,
the largest groups of sunspots ever
seen appeared on the surface of the
Sun, covering an area nearly 40 times
the surface area of the Earth. It was a
spectacular sight. Largely by
chance it was found that the
sunspots were also pouring
out energy in the form of radio
waves. Visible light and radio
waves are of course closely
allied, both being forms of
electromagnetic radiation.
(In time we would learn to
collect and read messages in a
number of other closely linked
languages, such as microwaves,
infrared and ultraviolet
radiation, X-rays and gamma
radiation, but I’ll save that for
another column).
The idea that various objects
in the cosmos might be sending
out radio signals was not
entirely new. In the 1930s, Karl
Jansky and Grote Reber had
independently detected radio‘noise’ coming from the Milky Way. But
astronomers took very little notice. The
two men were, after all, radio engineers,
not astronomers, so what would they
know? And in any case, how could such
emissions be generated? There was no
known mechanism.
World War II followed soon after,
stimulating further development of
radio technology and deployment
of radar, used to detect aircraft and
ships at great distances. From time to
time, odd signals were picked by radar
sets that could be interpreted as radio
emissions from the Sun or elsewhere.
But nothing was really clear, and there
were more pressing matters to attend to.
The war done, some researchers,
including in Australia, began using radar
receivers to pursue some of those earlier
observations. One such set up was on
the coast near Sydney. Radio waves are
of much greater wavelengths than light,
so the ‘images’ produced were inevitably
much fuzzier. The researchers, many ofby David Ellyard DISCOVERIESNASA/ESA
The SOHO spacecraft
snapped this huge sunspot group on October 28, 2003.