dr martin hendry dept of physics and astronomy, university of glasgow
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Captain Cook and the Cosmic Yardstick. Dr Martin Hendry Dept of Physics and Astronomy, University of Glasgow. James Cook (1728 – 1779). Retrograde motion of Mars. Ptolemy proposed an Earth-centred Universe. Ptolemy: 90 – 168 AD. Nicolaus Copernicus (1473 – 1543). - PowerPoint PPT PresentationTRANSCRIPT
Dr Martin HendryDr Martin HendryDept of Physics and Astronomy, Dept of Physics and Astronomy, University of GlasgowUniversity of Glasgow
Captain Cook Captain Cook and and thethe
Cosmic Cosmic YardstickYardstick
James Cook (1728 – 1779)
Retrograde motion of Mars
Ptolemy: 90 – 168 AD
Ptolemy proposed an Earth-centred Universe
NicolausCopernicus
(1473 – 1543)
“In the true centre of everything resides the Sun”
The Copernican RevolutionThe Copernican Revolution
Galileo Galilei:(1564 – 1642)
The Observations of GalileoThe Observations of Galileo
Moons of Jupiter: supported idea of Earth moving through space,contradicted Aristotelian view of all motions around Earth
The Observations of GalileoThe Observations of Galileo
The Observations of GalileoThe Observations of Galileo
Earlier observed phases of Venus
Geocentric model
Sun
The Observations of GalileoThe Observations of Galileo
Earlier observed phases of Venus
Geocentric model Heliocentric model
Sun
Sun
The Observations of GalileoThe Observations of Galileo
Earlier observed phases of Venus
The Observations of GalileoThe Observations of Galileo
Phases of Venus impossible to explain in an Earth-centred model
Clear evidence that the Earth went round the Sun, and not the other way round
Getting the Measure of the Solar System
Planet Distance
Mercury 0.39
Venus 0.72
Earth 1.00
Mars 1.52
Jupiter 5.20
Saturn 9.54
Getting the Measure of the Solar System
Planet Distance
Mercury 0.39
Venus 0.72
Earth 1.00
Mars 1.52
Jupiter 5.20
Saturn 9.54
How far is an astronomical unit?…How far is an astronomical unit?…
Johannes Kepler predicted a transit of Mercury on 29th May 1607
Instead, he ‘discovered’ sunspots
Johannes Kepler predicted a transit of Mercury on 29th May 1607
Instead, he ‘discovered’ sunspots
May 7th 2003: Transit of Mercury
Pierre Gassendi (1592 – 1655)
Observed a transit of Mercury on 7th November 1631
Predicted by Kepler in 1629, although he didn’t live to see it
November 24th 1639
Jeremiah Horrocks (c1619 – 1641)
“The Founder of English Astronomy”(Eyre Crowe, Walker Art Gallery)
William Crabtree (1610 - 1644)
“Crabtree watching the transit of Venus”(Ford Madox Brown, Manchester Town Hall)
Edmond Halley (1656 - 1742)
Halley travelled to St Helena in 1677, to map the Southern Skies
He observed a transit of Mercury on November 7th
Transit observations could measure the astronomical unit!
Edmond Halley (1656 - 1742)
Halley travelled to St Helena in 1677, to map the Southern Skies
He observed a transit of Mercury on November 7th
Transit observations could measure the astronomical unit!
Method relied on an accurate estimate for the radius of the Earth
In 1669 Jean Picard (1620 – 1682) measured
km6365ER (0.2% error)
Edmond Halley (1656 - 1742)
In 1716 Edmond Halley appealed to astronomers to observe the Venus transits of 1761 and 1769
Edmond Halley (1656 - 1742)
In 1716 Edmond Halley appealed to astronomers to observe the Venus transits of 1761 and 1769
He predicted the astronomical unit could be measured to an accuracy of 1 part in 500
Neville Maskelyne
(1732 - 1811)
“I am afraid we must wait till the next transit, in 1769…before astronomers will be able to do justice to Dr Halley’s noble proposal”
Captain James Cook
The 3rd June 1769 Venus Transit
Captain James Cookset sail for Tahiti in August 1768, onboard the Endeavour with astronomer Charles Green
Captain James Cook
The 3rd June 1769 Venus Transit
Endeavour arrived in Tahiti on 13th April 1769 – constructed a fort, and an observatory, at Point Venus
Captain James Cook
The 3rd June 1769 Venus Transit
Endeavour arrived in Tahiti on 13th April 1769 – constructed a fort, and an observatory, at Point Venus
Transit observed by Cook, Green and Solander
Captain James Cook
The 3rd June 1769 Venus Transit: Tahiti
The 3rd June 1769 Venus Transit
Father Maxmilian Hell(1720-1792) observed the transit from Lapland
Captain James Cook
The 3rd June 1769 Venus Transit
After years of analysis, the results of the 1769 observations were published.
e.g. Thomas Hornsby (1771):-
Cassini de Thury
1 A.U. = 93,726,900 miles
(between 90 and 94 million miles)
“Happy is our Century, to which has been reserved the glory of being witness to an event which will render it memorable in the annals of the Sciences!”