Download A Short History of Astronomy

A Short History of Astronomy
Or, what was in Cooks’ secret
‘sealed package’ and why is
Venus relevant to Australia?
Australian Aboriginal Astronomy
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"Ngaut Ngaut" on the banks of the Murray River. These engravings show a series of
dots and lines carved in the rock, which, according to the traditional owners, show the
"cycles of the Moon”.
http://www.atnf.csiro.au/research/AboriginalAstronomy/Examples/NgautNgaut.htm
Astronomy started with the naming of the celestial objects, and
later the recording of their movements in almanacs.
• 2300BC The Chinese astronomers started star naming
• 750BC Babylonians astronomers recognize the 18.6 year cycles in the rising and
setting of the Moon.
• 585BC Thales predicts a solar eclipse.
• Thales was a brilliant mathematician/scientist/philosopher of the day, who rejected
supernatural explanations in preference to natural explanations.
• The ability to mathematically predict a Cosmic event of such magnitude, propelled
astronomers into the industry of astrology, where they were employed by the rich
to cast horoscopes. (and the desire to keep the job or ones head , probably led to
the development of the The Barnum Statement, still used by astrologers today)
• Even the great mathematician and scientist Johannes Kepler compiled
prognostications for the Emperor, as a justified means of supplementing his
meager income.
• But more on Kepler later.
Geocentric or Heliocentric?
• This debate was perpetuated for well over a millennium, due to
the need to overturn religious doctrines.
• 388BC Plato - Geocentric in perfect circles.
• 270BC Aristarcus of Samos - Heliocentric
• 1250CE Najm al-Din al-Qazwini al Katibi - Heliocentric
• 1543CE Nicholaus Copernicus - Heliocentric and retains Plato’s
idea of perfect circles.
• 1610 Galileo Galilei builds a telescope, and confirms by
observation, that the Earth moves around the Sun.
• It took the Catholic Church a further 350 years to concede that
Galileo was right!
Galileo and his
telescope
1609CE
Back to Kepler and his
Three Laws of Planetary Motion.
1. Planets move in elliptical orbits around the sun.
2. Planets sweep out equal areas in equal times.
3. The square of the time a planet takes to go around
the sun, is proportional to the cube of its distance
from the Sun.
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This last law is imortant, but the problem lay with
the lack of a method to calculate the distance from
the Earth to the Sun.
The Transit of Venus
• Kepler calculated a transit of Venus would
occur in 1631, which was not observed.
• An exceptional mathematician, Jerimiah
Horrocks calculated that a second transit of
Venus would occur in 1639.
• Horrock’s was the first person (one of only
two) to accurately observe and record the
second transit.
• An act which set into motion the biggest
scientific mission the world had ever seen.
Horrock’s entered Cambridge at age 13 and made his
observation of the Transit of Venus at age 20.
Edmond Halley has an idea!
• In this famous paper,
Halley explained his
idea that the duration of
the transit of Venus be
observed from different
parts of the earth, and
then the distance to the
sun, (1AU) could be
determined with simple
geometry.
A plan is drawn up.
• 50 years before the event, Halley calculated
the next transit of Venus, due in 1761, and
proposed suitable places for observation.
• In the preceding years, over 100 teams of
astronomers made preparations to observe
the transit of Venus from far flung places.
• This next piece of astronomical history was
not going pass un-noticed.
The First Global Astronomical Collaboration.
• According to Richard Proctor, the 19th
Century Astronomical writer, 176
Astronomers in 117 locations around the
world participated.
• Why all the excitement?
• Because once the distance from the Earth
to the Sun (AU) was accurately
benchmarked, Kepler’s Third Law could be
used to calculate the distance from the sun
to all the other planets.
• 1AU = 149597870 km (mean)
A second attempt!
• Transits of Venus occur in pairs, eight years
apart, separated by gaps of around 100
years.
• Sadly errors in timing the transit meant
Astronomers were not happy with the
results of the 1761 observations and so
made preparations for the transit of 1769.
• In 1768 King George III granted the Royal
Society £4,000 for the South Sea Voyage
and the Admiralty agreed to provide a ship.
Enter Captain James Cook
• His ability as capable mariner, navigator and
scientist, via observations of a solar eclipse in
1766, brought Cook to the attention of the Royal
Society. He was subsequently appointed the
task of observing the Transit of Venus from
Tahiti. A location recommended by Halley.
• Cook was also directed by the Admiralty to
carry out secret instructions held in ‘a sealed
package’, on completion of the scientific
observations.
The ‘Secret’ Agenda.
• On 30 July 1768, the Lords of the Admiralty signed
Cooks instructions for the Endeavor voyage, and they
were classified as secret. The Admiralty’s sealed
instructions held the reasons for supporting his voyage:
in addition to observing the transit of Venus, Cook was
commanded to find ‘the Great South Land’, a land of
great extent that was thought to exist in southern
latitudes: :”You are to proceed to the Southward in
order to make discovery of the Continent abovementioned until you arrive in the latitude of 40deg,
unless you sooner fall in with it.”
Science and Politics
• The Royal Society and the Admiralty agreed on a
joint venture in which Britain's territorial
ambitions could be concealed behind the more
benign exploratory goal of expanding knowledge
of the solar system.
• The ploy worked and Cooks expedition slipped
under the radar of the French and Portuguese,
who were already active in the Pacific.
• Modern Australia owes its existence to a celestial
event!
William Parkinson Wilson
• Wilson was one of four founding
professors at Melbourne University.
• He established an observatory in
Mornington as part of the transit of
Venus observations on 9 December
1874.
• He had written a report of his findings to
his friend Robert Ellery, when on 11
December he died of apoplexy, aged 48.
• He is buried in the Moorooduc cemetery.