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. Early Greek Astronomy. The Greeks inherited ideas from Babylonia and Egypt, but approached astronomy in a scientific way. - PowerPoint PPT PresentationTRANSCRIPT
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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 thetheCosmic Cosmic YardstickYardstick
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James Cook (1728 – 1779)
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Retrograde motion of Mars
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Early Greek AstronomyEarly Greek AstronomyThe Greeks inherited ideas from Babylonia and Egypt, but approached astronomy in a scientific way
Plato (428 – 347 BC): Plato (428 – 347 BC): reality a distorted reality a distorted shadow of a shadow of a Perfect Perfect FormForm..
Circle = most perfect form in nature
All celestial motions are combinations of circular motions
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Aristotle (384 – 322 BC):Aristotle (384 – 322 BC):
Universe divided into two parts:
Corrupt, changeable Earth
Perfect, immutable heavens
Early Greek AstronomyEarly Greek AstronomyThe Greeks inherited ideas from Babylonia and Egypt, but approached astronomy in a scientific way
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Ptolemy: 90 – 168 AD
Ptolemy proposed a model which could explain planetary motions – including retrograde loops
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John of Holywood (c. 1200)
Author of ‘The Sphere’, standard textbook on spherical trigonometry
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NicolausCopernicus
(1473 – 1543)
“In the true centre of everything resides the Sun”
De Revolutionibus Orbis (1543)
The Copernican RevolutionThe Copernican Revolution
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The Copernican RevolutionThe Copernican Revolution
Simpler explanation why Venus and Mercury appear close to the Sun
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Tycho Brahe(1546-1601)
Uraniborg observatoryHven, between Denmark and Sweden
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Uraniborg observatoryHven, between Denmark and Sweden
Tycho Brahe(1546-1601)
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Tycho Brahe(1546-1601)
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Johannes Kepler(1571-1630) ‘Mysterium
Cosmographicum’ published in 1596
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Johannes Kepler(1571-1630)
’New Astronomy’ published in 1609
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The Spectacle Vendor by Johannes Stradanus, The Spectacle Vendor by Johannes Stradanus, 15821582
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Hans Lippershey’s 1608 patent of a device for
"seeing faraway things as though nearby."
Porta’s sketch of a telescope, August 1609
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Galileo Galilei:(1564 – 1642)
The Observations of GalileoThe Observations of Galileo
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Autumn/Winter 1609, observed: Craters of the Moon Moons of Jupiter Phases of Venus
Published in 1610 ‘Sidereus Nuncius’ (The Starry Messenger)
In conflict with Aristotelian / Ptolemaic Universe
The Observations of GalileoThe Observations of Galileo
Galileo Galilei:(1564 – 1642)
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The Moon is an imperfect world with mountains and valleys, just like the Earth
The Observations of GalileoThe Observations of Galileo
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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
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The Observations of GalileoThe Observations of GalileoEarlier observed phases of Venus
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Geocentric model Sun
The Observations of GalileoThe Observations of GalileoEarlier observed phases of Venus
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Geocentric model Heliocentric model Sun
Sun
The Observations of GalileoThe Observations of GalileoEarlier observed phases of Venus
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The Observations of GalileoThe 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”
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Getting the Measure of the Solar SystemIn the Heliocentric model it was easy to
determine the relative distances of the planets, using the geometry and trigonometry of the Greeks…
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Earth
Sun
Venus
We can use Pythagoras’ theorem!!
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Getting the Measure of the Solar System
Planet Distance
Mercury 0.39Venus 0.72Earth 1.00Mars 1.52Jupiter 5.20Saturn 9.54
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Getting the Measure of the Solar System
Planet Distance
Mercury 0.39Venus 0.72Earth 1.00Mars 1.52Jupiter 5.20Saturn 9.54
How far is an astronomical unit?…How far is an astronomical unit?…
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Eratosthenes: (c 276 – 195 BC)Eratosthenes: (c 276 – 195 BC)
360501
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Eratosthenes: (c 276 – 195 BC)Eratosthenes: (c 276 – 195 BC)
360501
Syene – Alexandria = 5000 stadia
Circumference of the Earth = 250000 stadia
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Aristarchus (310 – 230 Aristarchus (310 – 230 BC):BC):Earth – Moon distance Earth – Moon distance from eclipse geometryfrom eclipse geometry
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Aristarchus (310 – 230 Aristarchus (310 – 230 BC):BC):Earth – Sun distance Earth – Sun distance from phases of the Moonfrom phases of the Moon
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Aristarchus (310 – 230 Aristarchus (310 – 230 BC):BC):Earth – Sun distance Earth – Sun distance from phases of the Moonfrom phases of the Moon
Sound method, but angle between Sun and Moon hard to measure precisely.
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Aristarchus (310 – 230 Aristarchus (310 – 230 BC):BC):Earth – Sun distance Earth – Sun distance from phases of the Moonfrom 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
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A B
A and B line up the tree with different mountains, because they see it along different lines of sight
Parallax Shift
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Parallax Shift
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Parallax Shift
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Parallax Shift
Nearby stars do show an annual parallax shift, but it is tiny! First detected only in the mid 19th Century.
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Even the nearest star shows a parallax shift of only 1/2000th the width of the full Moon
Parallax Shift
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Even the nearest star shows a parallax shift of only 1/2000th the width of the full Moon
Parallax Shift
But parallax would be the key to measuring the A.U…
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Johannes Kepler predicted a transit of Mercury on 29th May 1607
Instead, he ‘discovered’ sunspots
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Johannes Kepler predicted a transit of Mercury on 29th May 1607
Instead, he ‘discovered’ sunspots
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May 7th 2003: Transit of Mercury
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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
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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 itKepler also predicted a transit of Venus in December 1631, but it occurred after Sunset in Europe
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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)
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Edmond Halley (1656 - 1742)
Halley travelled to St Helena in 1677, to map the Southern SkiesHe observed a transit of Mercury on November 7th
Transit observations could measure the astronomical unit!
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Edmond Halley (1656 - 1742)
Halley travelled to St Helena in 1677, to map the Southern SkiesHe observed a transit of Mercury on November 7th
Transit observations could measure the astronomical unit!
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Method relied on an accurate estimate for the radius of the Earth
In 1669 Jean Picard (1620 – 1682) measuredkm6365ER (0.2% error)
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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
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“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)
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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 1769He predicted the astronomical unit could be measured to an accuracy of 1 part in 500
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The 6th June 1761 Venus Transit
o Observations meticulously planned, for many yearso ‘Public outreach’ description by James Fergusono Franco-British cooperation, despite being at war!o 120 astronomers observed from about 60 locations
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o Observations meticulously planned, for many yearso ‘Public outreach’ description by James Fergusono Franco-British cooperation, despite being at war!o 120 astronomers observed from about 60 locations
The 6th June 1761 Venus Transit
o Results were disappointing: Bad weather Poor global coverage ‘Black Drop Effect’ Systematic errors
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The 6th June 1761 Venus Transit
o Results were disappointing:
o Astronomical Unit lay between 77 million and 97 million miles (20% uncertainty)
Bad weather Poor global coverage ‘Black Drop Effect’ Systematic errors
o Observations meticulously planned, for many yearso ‘Public outreach’ description by James Fergusono Franco-British cooperation, despite being at war!o 120 astronomers observed from about 60 locations
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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”
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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
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John Harrison
‘H4’1763
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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
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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
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Captain James Cook
The 3rd June 1769 Venus Transit: Tahiti
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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
The Endeavour explored for two more years, before returning to Britain. During the voyage Charles Green died of malaria.
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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
The Endeavour explored for two more years, before returning to Britain. During the voyage Charles Green died of malaria.
Jean Baptiste Chappe d’Auteroche died of typhus on 1st August 1769, in Baja California
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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
The Endeavour explored for two more years, before returning to Britain. During the voyage Charles Green died of malaria.
Jean Baptiste Chappe d’Auteroche died of typhus on 1st August 1769, in Baja California
Guillaume-Joseph-Hyacinthe-Jean-Baptiste Le Gentil wins the award for the unluckiest astronomer!
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Captain James Cook
The 3rd June 1769 Venus Transit: Vardö, in Lapland
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The 3rd June 1769 Venus Transit
Father Maxmilian Hell(1720-1792) observed the transit from Lapland
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3rd June 1769
20:34 UT
Internal contact at Vardö…
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3rd June 1769
20:34 UT
Internal contact at Vardö…
…meanwhile in Tahiti…
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3rd June 1769
20:43 UT
Internal contact in Tahiti…
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3rd June 1769
20:45 UT
Internal contact in Tahiti…
…meanwhile at Vardö…
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4th June 1769
02:22 UT
Internal contact in Tahiti…
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4th June 1769
02:22 UT
Internal contact in Tahiti…
…meanwhile at Vardö…
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4th June 1769
02:33 UT
Internal contact in at Vardö…
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4th June 1769
02:33 UT
Internal contact in at Vardö…
…meanwhile in Tahiti…
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The 3rd June 1769 Venus Transit
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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!”
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Captain James Cook
Venus Abandoned
In the 19th Century, astronomers’ attention switched to Mars.o Easier to measure positions at night!o Mars appeared smaller in sizeo No ‘time limit’ on observationso No black drop or atmospheric effects
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View from 0 N, 0 Wo o
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View from 0 N, 180 W (opposite side of the Earth)oo
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Captain James Cook
Venus Abandoned
David Gill (1843 – 1914)
Measured the parallax of Mars from Ascension
Island in 1877
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Captain James Cook
Venus Abandoned
David Gill (1843 – 1914)
Measured the parallax of Mars from Ascension
Island in 1877
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Captain James Cook
Venus Abandoned
David Gill (1843 – 1914)
Measured the parallax of Mars from Ascension
Island in 1877
Gill’s observations narrowed the range for 1 A.U.:-
Between 92,981,000 miles and 93,235,600 milesSuperceded the photographic observations of Venus transits in 1874 and 1882
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Captain James Cook
Venus Reclaimed
Observations of the Near-Earth asteroid Eros allowed even greater precision
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Captain James Cook
Venus Reclaimed
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)
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Captain James Cook
Venus Reclaimed
Irwin ShapiroBounced RADAR echoes from Venus in 1968
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Captain James Cook
Venus Reclaimed
Irwin ShapiroBounced RADAR echoes from Venus in 1968 In 1976 IAU adopted:-
1 A.U. = 92,958,329 miles
= 149,597,870 km
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Captain James Cook
Venus Reclaimed
Irwin ShapiroBounced 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
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Faro – Helsinki, 3479 km
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Waikoloa, Hawaii
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