Transcript venus - University of Glasgow
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: 90 – 168 AD
Ptolemy proposed an
Earth-centred
Universe
The Copernican Revolution
Nicolaus Copernicus (1473 – 1543)
“In the true centre of everything resides the Sun”
The Observations of Galileo
Galileo Galilei: (1564 – 1642)
The Observations of Galileo
Moons of Jupiter: supported idea of Earth moving through space, contradicted Aristotelian view of all motions around Earth
The Observations of Galileo
Earlier observed phases of Venus
The Observations of Galileo
Earlier observed phases of Venus Geocentric model Sun
The Observations of Galileo
Earlier observed phases of Venus Geocentric model Sun Heliocentric model Sun
The 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
Mercury Venus Earth Mars Jupiter Saturn
Distance
0.39
0.72
1.00
1.52
5.20
9.54
Getting the Measure of the Solar System
Planet
Mercury Venus Earth Mars Jupiter Saturn
Distance
0.39
0.72
1.00
1.52
5.20
9.54
How far is an astronomical unit?…
Johannes Kepler predicted a transit of Mercury on 29 th May 1607 Instead, he ‘discovered’ sunspots
Johannes Kepler predicted a transit of Mercury on 29 th May 1607 Instead, he ‘discovered’ sunspots
May 7
th
2003: Transit of Mercury
Pierre Gassendi (1592 – 1655) Observed a transit of Mercury on 7 th November 1631 Predicted by Kepler in 1629, although he didn’t live to see it
November 24 th 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)
Halley travelled to St Helena in 1677, to map the Southern Skies He observed a transit of Mercury on November 7 th Edmond Halley (1656 - 1742) Transit observations could measure the astronomical unit!
Halley travelled to St Helena in 1677, to map the Southern Skies He observed a transit of Mercury on November 7 th Edmond Halley (1656 - 1742) 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
R E
6365 km (0.2% error)
Edmond Halley (1656 - 1742) In 1716 Edmond Halley appealed to astronomers to observe the Venus transits of 1761 and 1769
In 1716 Edmond Halley appealed to astronomers to observe the Venus transits of 1761 and 1769 Edmond Halley (1656 - 1742) 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”
The 3 rd June 1769 Venus Transit Captain James Cook set sail for Tahiti in August 1768, onboard the Endeavour with astronomer Charles Green Captain James Cook
The 3 rd June 1769 Venus Transit Endeavour arrived in Tahiti on 13 th April 1769 – constructed a fort, and an observatory, at Point Venus Captain James Cook
The 3 rd June 1769 Venus Transit Endeavour arrived in Tahiti on 13 th April 1769 – constructed a fort, and an observatory, at Point Venus Transit observed by Cook, Green and Solander Captain James Cook
The 3 rd June 1769 Venus Transit: Tahiti Captain James Cook
The 3 rd June 1769 Venus Transit Father Maxmilian Hell (1720-1792) observed the transit from Lapland
The 3 rd June 1769 Venus Transit After years of analysis, the results of the 1769 observations were published.
e.g. Thomas Hornsby (1771): 1 A.U. = 93,726,900 miles Cassini de Thury “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!”