Dr Martin Hendry

Dept of Physics and Astronomy, University of GlasgowCaptain Cook and theCosmic Yardstick

James Cook (1728 1779)

Retrograde motion of Mars

Early Greek AstronomyThe Greeks inherited ideas from Babylonia and Egypt, but approached astronomy in a scientific wayPlato (428 347 BC): reality a distorted shadow of a Perfect Form.

Circle = most perfect form in natureAll celestial motions are combinations of circular motions

Aristotle (384 322 BC):

Universe divided into two parts:

Corrupt, changeable Earth

Perfect, immutable heavensEarly Greek AstronomyThe Greeks inherited ideas from Babylonia and Egypt, but approached astronomy in a scientific way

Ptolemy: 90 168 ADPtolemy 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

NicolausCopernicus (1473 1543)In the true centre of everything resides the SunDe Revolutionibus Orbis (1543)The Copernican Revolution

The Copernican RevolutionSimpler explanation why Venus and Mercury appear close to the Sun

Tycho Brahe(1546-1601)Uraniborg observatoryHven, between Denmark and Sweden

Uraniborg observatoryHven, between Denmark and SwedenTycho Brahe(1546-1601)

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 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 VenusPublished in 1610 Sidereus Nuncius (The Starry Messenger)In conflict with Aristotelian / Ptolemaic UniverseThe Observations of GalileoGalileo Galilei:(1564 1642)

The Moon is an imperfect world with mountains and valleys, just like the EarthThe Observations of Galileo

Moons of Jupiter: supported idea of Earth moving through space,contradicted Aristotelian view of all motions around EarthThe Observations of Galileo

The Observations of GalileoEarlier observed phases of Venus

Geocentric model SunThe Observations of GalileoEarlier observed phases of Venus

Geocentric model Heliocentric model SunSunThe Observations of GalileoEarlier observed phases of Venus

The Observations of GalileoPhases of Venus impossible to explain in geocentric modelClear evidence that the Earth went round the Sun, and not the other way roundCynthiae figuras aemulatur mater amorum

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

EarthSunVenusWe can use Pythagoras theorem!!

Getting the Measure of the Solar SystemPlanetDistance

Mercury0.39

Venus0.72

Earth1.00

Mars1.52

Jupiter5.20

Saturn9.54

Getting the Measure of the Solar SystemPlanetDistance

Mercury0.39

Venus0.72

Earth1.00

Mars1.52

Jupiter5.20

Saturn9.54How far is an astronomical unit?

Eratosthenes: (c 276 195 BC)

Eratosthenes: (c 276 195 BC)Syene Alexandria = 5000 stadiaCircumference of the Earth = 250000 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 MoonSound method, but angle between Sun and Moon hard to measure precisely.

Aristarchus (310 230 BC):

Earth Sun distance from phases of the MoonSound 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

ABA and B line up the tree with different mountains, because they see it along different lines of sightParallax Shift

Parallax Shift

Parallax Shift

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

Even the nearest star shows a parallax shift of only 1/2000th the width of the full MoonParallax Shift

Even the nearest star shows a parallax shift of only 1/2000th the width of the full MoonParallax ShiftBut parallax would be the key to measuring the A.U

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 didnt live to see it

Pierre Gassendi (1592 1655)

Observed a transit of Mercury on 7th November 1631

Predicted by Kepler in 1629, although he didnt live to see itKepler also predicted a transit of Venus in December 1631, but it occurred after Sunset in Europe

November 24th 1639Jeremiah 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 7thTransit 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 7thTransit observations could measure the astronomical unit!

Method relied on an accurate estimate for the radius of the EarthIn 1669 Jean Picard (1620 1682) measured(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

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)

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

The 6th June 1761 Venus Transit Observations meticulously planned, for many years

Public outreach description by James Ferguson

Franco-British cooperation, despite being at war!

120 astronomers observed from about 60 locations

Observations meticulously planned, for many years

Public outreach description by James Ferguson

Franco-British cooperation, despite being at war!

120 astronomers observed from about 60 locationsThe 6th June 1761 Venus Transit Results were disappointing: Bad weather Poor global coverage Black Drop Effect Systematic errors

The 6th June 1761 Venus Transit Results were disappointing: Astronomical Unit lay between 77 million and 97 million miles (20% uncertainty) Bad weather Poor global coverage Black Drop Effect Systematic errors Observations meticulously planned, for many years

Public outreach description by James Ferguson

Franco-British cooperation, despite being at war!

120 astronomers observed from about 60 locations

Neville Maskelyne (1732 - 1811)I am afraid we must wait till the next transit, in 1769before astronomers will be able to do justice to Dr Halleys noble proposal

Captain James CookThe 3rd June 1769 Venus TransitCaptain James Cookset sail for Tahiti in August 1768, onboard the Endeavour with astronomer Charles Green

John HarrisonH41763

Captain James CookThe 3rd June 1769 Venus TransitEndeavour arrived in Tahiti on 13th April 1769 constructed a fort, and an observatory, at Point Venus

Captain James CookThe 3rd June 1769 Venus TransitEndeavour 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 CookThe 3rd June 1769 Venus Transit: Tahiti

Captain James CookThe 3rd June 1769 Venus TransitEndeavour 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.

Captain James CookThe 3rd June 1769 Venus TransitEndeavour 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 dAuteroche died of typhus on 1st August 1769, in Baja California

Captain James CookThe 3rd June 1769 Venus TransitEndeavour 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 dAuteroche died of typhus on 1st August 1769, in Baja CaliforniaGuillaume-Joseph-Hyacinthe-Jean-Baptiste Le Gentil wins the award for the unluckiest astronomer!

Captain James CookThe 3rd June 1769 Venus Transit: Vard, in Lapland

The 3rd June 1769 Venus TransitFather Maxmilian Hell(1720-1792) observed the transit from Lapland

3rd June 1769

20:34 UT

Internal contact at Vard

3rd June 1769

20:34 UT

Internal contact at Vard

meanwhile in Tahiti

3rd June 1769

20:43 UT

Internal contact in Tahiti

3rd June 1769

20:45 UT

Internal contact in Tahiti

meanwhile at Vard

4th June 1769

02:22 UT

Internal contact in Tahiti

4th June 1769

02:22 UT

Internal contact in Tahiti

meanwhile at Vard

4th June 1769

02:33 UT

Internal contact in at Vard

4th June 1769

02:33 UT

Internal contact in at Vard

meanwhile in Tahiti

The 3rd June 1769 Venus Transit

Captain James CookThe 3rd June 1769 Venus TransitAfter years of analysis, the results of the 1769 observations were published.

e.g. Thomas Hornsby (1771):-

Cassini de Thury1 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 CookVenus AbandonedIn the 19th Century, astronomers attention switched to Mars.

Easier to measure positions at night! Mars appeared smaller in size No time limit on observations No black drop or atmospheric effects

View from 0 N, 0 Woo

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

Captain James CookVenus AbandonedDavid Gill (1843 1914)

Measured the parallax of Mars from Ascension Island in 1877

Captain James CookVenus AbandonedDavid Gill (1843 1914)

Measured the parallax of Mars from Ascension Island in 1877

Captain James CookVenus AbandonedDavid Gill (1843 1914)

Measured the parallax of Mars from Ascension Island in 1877Gills 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

Captain James CookVenus ReclaimedObservations of the Near-Earth asteroid Eros allowed even greater precision

Captain James CookVenus ReclaimedObservations of the Near-Earth asteroid Eros allowed even greater precisionHarold Spencer Jones (1900 1960)

1 A.U. = 93,005,000 miles(less than 0.1% uncertainty)

Captain James CookVenus ReclaimedIrwin ShapiroBounced RADAR echoes from Venus in 1968

Captain James CookVenus ReclaimedIrwin ShapiroBounced RADAR echoes from Venus in 1968In 1976 IAU adopted:-

1 A.U. = 92,958,329 miles = 149,597,870 km

Captain James CookVenus ReclaimedIrwin ShapiroBounced RADAR echoes from Venus in 1968

Shapiro Effect time delay also a test of General RelativityIn 1976 IAU adopted:-

1 A.U. = 92,958,329 miles = 149,597,870 km

Faro Helsinki, 3479 km

Waikoloa, Hawaii