Transcript cook - 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
Early Greek Astronomy
The Greeks inherited ideas from Babylonia and Egypt, but approached astronomy in a scientific way
Plato (428 – 347 BC): reality a distorted shadow of a Perfect Form.
Circle = most perfect form in nature All celestial motions are combinations of circular motions
Early Greek Astronomy
The Greeks inherited ideas from Babylonia and Egypt, but approached astronomy in a scientific way
Aristotle (384 – 322 BC):
Universe divided into two parts: Corrupt, changeable Earth Perfect, immutable heavens
Ptolemy: 90 – 168 AD
Ptolemy proposed a model which could explain planetary motions – including retrograde loops
John of Holywood (c. 1200) Author of ‘The Sphere’, standard textbook on spherical trigonometry
The Copernican Revolution
Nicolaus Copernicus (1473 – 1543)
“In the true centre of everything resides the Sun”
De Revolutionibus Orbis (1543)
The Copernican Revolution
Simpler explanation why Venus and Mercury appear close to the Sun
Tycho Brahe (1546-1601)
Uraniborg observatory Hven, between Denmark and Sweden
Tycho Brahe (1546-1601)
Uraniborg observatory Hven, between Denmark and Sweden
Tycho Brahe (1546-1601)
Johannes Kepler (1571-1630) ‘Mysterium Cosmographicum’ published in 1596
Johannes Kepler (1571-1630) ’New Astronomy’ published in 1609
The Spectacle Vendor by Johannes Stradanus, 1582
Hans Lippershey’s 1608 patent of a device for "seeing faraway things as though nearby." Porta’s sketch of a telescope, August 1609
The Observations of Galileo
Galileo Galilei: (1564 – 1642)
The Observations of Galileo
Autumn/Winter 1609, observed:
Craters of the Moon Moons of Jupiter Phases of Venus
Galileo Galilei: (1564 – 1642)
In conflict with Aristotelian / Ptolemaic Universe Published in 1610 ‘Sidereus Nuncius’ (The Starry Messenger)
The Observations of Galileo The Moon is an imperfect world with mountains and valleys, just like the Earth
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 geocentric model Clear evidence that the Earth went round the Sun, and not the other way round
“Cynthiae figuras aemulatur mater amorum”
Getting the Measure of the Solar System
In the Heliocentric model it was easy to determine the
relative
distances of the planets, using the geometry and trigonometry of the Greeks…
Sun Earth Venus
We can use Pythagoras’ theorem!!
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?…
Eratosthenes: (c 276 – 195 BC)
1 50 360
Eratosthenes: (c 276 – 195 BC)
Syene – Alexandria = 5000 stadia Circumference of the Earth = 250000 stadia 1 50 360
Aristarchus (310 – 230 BC): Earth – Moon distance from eclipse geometry
Aristarchus (310 – 230 BC): Earth – Sun distance from phases of the Moon
Aristarchus (310 – 230 BC): Earth – Sun distance from phases of the Moon
Sound method, but angle between Sun and Moon hard to measure precisely.
Aristarchus (310 – 230 BC): Earth – Sun distance from phases of the Moon
Sound method, but angle between Sun and Moon hard to measure precisely.
Heliocentric model (Sun much larger than the Earth).
Not widely accepted, because no parallax shift
Parallax Shift
A B
A and B line up the tree with different mountains, because they see it along different lines of sight
Parallax Shift
Parallax Shift
Parallax Shift
Nearby stars
do
show an annual parallax shift, but it is tiny! First detected only in the mid 19
th
Century.
Parallax Shift
Even the nearest star shows a parallax shift of only 1/2000 th the width of the full Moon
Parallax Shift
Even the nearest star shows a parallax shift of only 1/2000 th the width of the full Moon
But parallax would be the key to measuring the A.U…
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
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 Kepler also predicted a transit of Venus in December 1631, but it occurred after Sunset in Europe
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)
Edmond Halley (1656 - 1742) Halley travelled to St Helena in 1677, to map the Southern Skies He observed a transit of Mercury on November 7 th 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 7 th 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 Halley presented a paper to the Royal Society, appealing to astronomers to observe the Venus transits of 1761 and 1769
Edmond Halley (1656 - 1742) “I recommend it, therefore, again and again, to those curious astronomers who (when I am dead) will have an opportunity of observing these things, that they would remember this my admonition, and diligently apply themselves with all their might to the making of this observation; and I earnestly wish them all imaginable success; in the first place that they may not – by the unseasonable obscurity of a cloudy sky – be deprived of this most desirable sight; and then, that having ascertained with more exactness the magnitudes of the planetary orbits, it may redound to their eternal fame and glory.”
Edmond Halley (1656 - 1742) In 1716 Halley presented a paper to the Royal Society, appealing 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
The 6 th June 1761 Venus Transit o o o Observations meticulously planned, for many years ‘Public outreach’ description by James Ferguson Franco-British cooperation, despite being at war!
o 120 astronomers observed from about 60 locations
The 6 th June 1761 Venus Transit o o o Observations meticulously planned, for many years ‘Public outreach’ description by James Ferguson Franco-British cooperation, despite being at war!
o 120 astronomers observed from about 60 locations o Results were disappointing: Bad weather Poor global coverage ‘Black Drop Effect’ Systematic errors
The 6 th June 1761 Venus Transit o o o Observations meticulously planned, for many years ‘Public outreach’ description by James Ferguson Franco-British cooperation, despite being at war!
o 120 astronomers observed from about 60 locations o o Results were disappointing: Bad weather Poor global coverage ‘Black Drop Effect’ Systematic errors Astronomical Unit lay between 77 million and 97 million miles (20% uncertainty)
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
John Harrison
‘H4’ 1763
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 Endeavour arrived in Tahiti on 13 th April 1769 – constructed a fort, and an observatory, at Point Venus The Endeavour explored for two more years, before returning to Britain. During the voyage 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 The Endeavour explored for two more years, before returning to Britain. During the voyage Captain James Cook Jean Baptiste Chappe d’Auteroche died of typhus on 1 st August 1769, in Baja California
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 The Endeavour explored for two more years, before returning to Britain. During the voyage Captain James Cook Jean Baptiste Chappe d’Auteroche died of typhus on 1 st August 1769, in Baja California Guillaume-Joseph-Hyacinthe-Jean-Baptiste Le Gentil wins the award for the unluckiest astronomer!
The 3 rd June 1769 Venus Transit: Vardö, in Lapland Captain James Cook
The 3 rd June 1769 Venus Transit Father Maxmilian Hell (1720-1792) observed the transit from Lapland
3 rd June 1769 20:34 UT Internal contact at Vardö…
3 rd June 1769 20:34 UT Internal contact at Vardö… …meanwhile in Tahiti…
3 rd June 1769 20:43 UT Internal contact in Tahiti…
3 rd June 1769 20:45 UT Internal contact in Tahiti… …meanwhile at Vardö…
4 th June 1769 02:22 UT Internal contact in Tahiti…
4 th June 1769 02:22 UT Internal contact in Tahiti… …meanwhile at Vardö…
4 th June 1769 02:33 UT Internal contact in at Vardö…
4 th June 1769 02:33 UT Internal contact in at Vardö… …meanwhile in Tahiti…
The 3 rd June 1769 Venus Transit
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!”
Venus Abandoned In the 19 th Century, astronomers’ attention switched to Mars.
o o o o Easier to measure positions at night!
Mars appeared smaller in size No ‘time limit’ on observations No black drop or atmospheric effects Captain James Cook
o o View from 0 N, 0 W
o o View from 0 N, 180 W (opposite side of the Earth)
Venus Abandoned Captain James Cook David Gill (1843 – 1914) Measured the parallax of Mars from Ascension Island in 1877
Venus Abandoned Captain James Cook David Gill (1843 – 1914) Measured the parallax of Mars from Ascension Island in 1877
Venus Abandoned Captain James Cook David Gill (1843 – 1914) Gill’s observations narrowed the range for 1 A.U.: Between 92,981,000 miles and 93,235,600 miles Measured the parallax of Mars from Ascension Island in 1877 Superceded the photographic observations of Venus transits in 1874 and 1882
Venus Reclaimed Captain James Cook Observations of the Near-Earth asteroid Eros allowed even greater precision
Venus Reclaimed Captain James Cook Observations of the Near-Earth asteroid Eros allowed even greater precision Harold Spencer Jones (1900 – 1960) 1 A.U. = 93,005,000 miles (less than 0.1% uncertainty)
Venus Reclaimed Captain James Cook Irwin Shapiro Bounced RADAR echoes from Venus in 1968
Venus Reclaimed Captain James Cook Irwin Shapiro Bounced RADAR echoes from Venus in 1968 In 1976 IAU adopted: 1 A.U. = 92,958,329 miles = 149,597,870 km
Venus Reclaimed Captain James Cook Irwin Shapiro Bounced RADAR echoes from Venus in 1968 ‘Shapiro Effect’ time delay also a test of General Relativity In 1976 IAU adopted: 1 A.U. = 92,958,329 miles = 149,597,870 km
Faro – Helsinki, 3479 km
Waikoloa, Hawaii