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| Two ways of watching the transit of Venus
– through a telescope fitted with a solar filter (above),
or viewing an image of the sun projected onto a screen (below) |
How far away is the Sun? In an attempt to answer this fundamental
question the British Admiralty sent Captain James Cook to Tahiti in
1769 measure the transit of Venus. This occurs when the planet comes
directly between the Earth and the Sun and so is visible as a black
spot, slowly moving across the face of the Sun. Through the application
of geometry, measuring the time the transit starts and finishes, as
seen from different parts of the Earth’s surface, it is then
possible to estimate the distance to the Sun. From Tahiti, Cook then
set sail to search for the great southern continent, to claim it for
the British crown.
Transits of Venus are rare events, occurring in pairs over a century
apart. The last transit was in 1882, so when the black dot of Venus
crossed the edge of the Sun on June 8th 2004 it was an event no
living person had witnessed. In Sydney that day Venus was in the
western sky, well placed for observation from UNSW. As Cook’s
landing place in Botany Bay is also visible from UNSW, the combination
of science and history was irresistible. We held a public viewing
of the transit, from the Scientia Building on the UNSW campus.
The ABC’s Jennifer Byrne compered and Aboriginal elder Uncle
Norm Newlin welcomed us to the land of the Eora people. Michael
Burton from the Department of Astrophysics, then described the science
of the transit and how it was used in an attempt to measure the
distance to the Sun (it turned out not to be easy with the instruments
available in Cook’s day). John Gascoigne, Head of the School
of History, then commented on the historical significance of the
event which lead to European colonisation of Australia. Finally
the Dean of Science, Mike Archer, talked about the impact of biological
discoveries made on Cook’s venture along the east coast of
Australia, and the unique flora and fauna that was recorded.
Four telescopes were placed along the balcony to show the transit
in different guises. One was used to project the Sun onto a large
screen, so that the progress of Venus could be gauged by all. Other
telescopes looked at the Sun through various filters, allowing a
direct view of the event, as well as of the solar weather. The fourth
telescope was directed towards the planet Jupiter, showing that
celestial bodies are indeed visible in the daytime if you know where
to look.
If you missed the big event, we get another chance in 2012, but
it’s a long wait to the next transit after that!
Michael Burton
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