Dr Martin Hendry Dept of Physics and Astronomy, University of Glasgow Captain Cook and the Cosmic Yardstick

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

Aristotle (384 – 322 BC): Universe divided into two parts: Corrupt, changeable Earth Perfect, immutable heavens Early Greek Astronomy The Greeks inherited ideas from Babylonia and Egypt, but approached astronomy in a scientific way

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

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 ( ) Uraniborg observatory Hven, between Denmark and Sweden

Uraniborg observatory Hven, between Denmark and Sweden Tycho Brahe ( )

Tycho Brahe ( )

Johannes Kepler ( ) Mysterium Cosmographicum published in 1596

Johannes Kepler ( ) New Astronomy published in 1609

The Spectacle Vendor by Johannes Stradanus, 1582

Hans Lippersheys 1608 patent of a device for "seeing faraway things as though nearby." Portas sketch of a telescope, August 1609

Galileo Galilei: (1564 – 1642) The Observations of Galileo

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 Galileo Galileo Galilei: (1564 – 1642)

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

Geocentric model Sun The Observations of Galileo Earlier observed phases of Venus

Geocentric modelHeliocentric model Sun The Observations of Galileo Earlier observed phases of Venus

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…

Earth Sun Venus We can use Pythagoras theorem!!

Getting the Measure of the Solar System PlanetDistance Mercury0.39 Venus0.72 Earth1.00 Mars1.52 Jupiter5.20 Saturn9.54

Getting the Measure of the Solar System PlanetDistance Mercury0.39 Venus0.72 Earth1.00 Mars1.52 Jupiter5.20 Saturn9.54 How far is an astronomical unit?…

Eratosthenes: (c 276 – 195 BC)

Syene – Alexandria = 5000 stadia Circumference of the Earth = stadia

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

A B A and B line up the tree with different mountains, because they see it along different lines of sight Parallax Shift

Nearby stars do show an annual parallax shift, but it is tiny! First detected only in the mid 19 th Century.

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 Parallax Shift 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 didnt 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 didnt 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 ( ) Crabtree watching the transit of Venus (Ford Madox Brown, Manchester Town Hall)

Edmond Halley ( ) 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 ( ) 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 (0.2% error)

Edmond Halley ( ) In 1716 Halley presented a paper to the Royal Society, appealing to astronomers to observe the Venus transits of 1761 and 1769

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 ( )

Edmond Halley ( ) 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 Observations meticulously planned, for many years o Public outreach description by James Ferguson o Franco-British cooperation, despite being at war! o 120 astronomers observed from about 60 locations

o Observations meticulously planned, for many years o Public outreach description by James Ferguson o Franco-British cooperation, despite being at war! o 120 astronomers observed from about 60 locations The 6 th June 1761 Venus Transit o Results were disappointing: Bad weather Poor global coverage Black Drop Effect Systematic errors

The 6 th 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 years o Public outreach description by James Ferguson o Franco-British cooperation, despite being at war! o 120 astronomers observed from about 60 locations

Neville Maskelyne ( ) I am afraid we must wait till the next transit, in 1769…before astronomers will be able to do justice to Dr Halleys noble proposal

Captain James Cook The 3 rd June 1769 Venus Transit Captain James Cook set sail for Tahiti in August 1768, onboard the Endeavour with astronomer Charles Green

John Harrison H4 1763

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 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 Charles Green died of malaria.

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 Charles Green died of malaria. Jean Baptiste Chappe dAuteroche died of typhus on 1 st August 1769, in Baja California

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 Charles Green died of malaria. Jean Baptiste Chappe dAuteroche 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!

Captain James Cook The 3 rd June 1769 Venus Transit: Vardö, in Lapland

The 3 rd June 1769 Venus Transit Father Maxmilian Hell ( ) observed the transit from Lapland

3 rd June :34 UT Internal contact at Vardö…

3 rd June :34 UT Internal contact at Vardö… …meanwhile in Tahiti…

3 rd June :43 UT Internal contact in Tahiti…

3 rd June :45 UT Internal contact in Tahiti… …meanwhile at Vardö…

4 th June :22 UT Internal contact in Tahiti…

4 th June :22 UT Internal contact in Tahiti… …meanwhile at Vardö…

4 th June :33 UT Internal contact in at Vardö…

4 th June :33 UT Internal contact in at Vardö… …meanwhile in Tahiti…

The 3 rd June 1769 Venus Transit

Captain James Cook The 3 rd 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!

Captain James Cook Venus Abandoned In the 19 th Century, astronomers attention switched to Mars. o Easier to measure positions at night! o Mars appeared smaller in size o No time limit on observations o No black drop or atmospheric effects

View from 0 N, 0 W oo

View from 0 N, 180 W (opposite side of the Earth) oo

Captain James Cook Venus Abandoned David Gill (1843 – 1914) Measured the parallax of Mars from Ascension Island in 1877

Captain James Cook Venus Abandoned David Gill (1843 – 1914) Measured the parallax of Mars from Ascension Island in 1877

Captain James Cook Venus Abandoned David Gill (1843 – 1914) Measured the parallax of Mars from Ascension Island in 1877 Gills observations narrowed the range for 1 A.U.:- Between 92,981,000 miles and 93,235,600 miles Superceded the photographic observations of Venus transits in 1874 and 1882

Captain James Cook Venus Reclaimed Observations of the Near-Earth asteroid Eros allowed even greater precision

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)

Captain James Cook Venus Reclaimed Irwin Shapiro Bounced RADAR echoes from Venus in 1968

Captain James Cook Venus Reclaimed Irwin Shapiro Bounced RADAR echoes from Venus in 1968 In 1976 IAU adopted:- 1 A.U. = 92,958,329 miles = 149,597,870 km

Captain James Cook Venus Reclaimed 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