The history and science of the Transit of Venus

Credit: Juan Manuel Pérez Rayego

太白金星 Venus

全天第三亮的天體

Doug Zubenel (TWAN)

Fred Espenak

Cenk E. Tezel & Tunc Tezel

晨星/昏星

Venus Feb - Sep 2010

大距

東大距

西大距

下合

上合 合

衝

內行星 vs 外行星

罕有的金星凌日

• 1631 December 7 • 1639 December 4

• 1761 June 6 • 1769 June 4

• 1874 December 9 • 1882 December 6

• 2004 June 8 • 2012 June 6

• 2117 December 11

Last chance in your life!

121.5 years

105.5 years

121.5 years

105.5 years

軌道周期: 金星 224日 地球 365日

金星與地球的軌道

地球與金星 的會合周期: 584日 (1.6年)

3.4° 夾角

Paper Plate Education

http://analyzer.depaul.edu/paperplate/

凌日階段 時間 太陽方向/方位角/仰角

日出 5時37分 東北偏東/065°/0°

Ⅰ 凌始外切 6時11分 東北偏東/068°/6°

Ⅱ 凌始內切 6時29分 東北偏東/069°/10°

凌甚 9時31分 西北偏西/081°/51°

Ⅲ 凌終內切 12時31分 西北偏西/278°/88°

Ⅳ 凌終外切 12時48分 西北偏西/274°/84°

2012年6月6日 金星凌日

不按比例

注意選擇適當的觀測地點

哥白尼 Nicolaus Copernicus (1473-1543)

天體運行論, 1543 De revolutionibus orbium coelestium

(On the Revolutions of the Celestial Spheres)

Thomas Digges, 1556 Thomas Trevelyon, 1608 "The true proportion of all the Planets"

第谷 Tycho Brahe (1546-1601)

開普勒 Johannes Kepler (1571-1630)

Kepler’s laws of planetary motion

• Law of ellipses – the orbit of a planet about the

sun is an ellipse with the sun at one focus

• Law of equal areas – a line joining a planet and the

sun sweeps out equal areas in equal intervals of time

• Law of harmonies – the square of a planet’s

sidereal period around the sun is directly proportional to the cube of the length of its orbit’s semi-major axis, a

a

The Rudolphine Tables by Johannes Kepler, 1627

Kepler predicted the Transit of Mercury on Nov 7, 1631 and Transit of Venus on Dec 6, 1631

行星與太陽平均距離 (以天文單位計算)

Copernicus Kepler 20th Century

Mercury 0.3763 0.389 0.387

Venus 0.7193 0.724 0.723

Earth 1.0000 1.000 1.000

Mars 1.5198 1.523 1.524

Jupiter 5.2192 5.200 5.202

Saturn 9.1743 9.510 9.539

1天文單位 (AU, Astronomical Unit) = 太陽與地球的距離

Pierre Gassendi (1592-1655)

• French • name "Aurora Borealis"

observed Transit of Mercury on Nov 7, 1631

Angular size VS real size

a much bigger solar system!

Jeremiah Horrocks (1618 - 1641)

• British • predicted and

observed the transit of Venus on Dec 4, 1639

William Crabtree

The only 2 people saw the Transit of Venus in 1639

Jeremiah Horrocks

Cosmotheoros by Christiaan Huygens, 1698

1 AU = ?

When Who How 1 AU =

3rd c BCE Aristarchos geometry 1,200 Earth Radius

2nd c CE Ptolemy " " 1,160 Earth Radius

1540 Copernicus " " 1,142 Earth Radius

1600 Tycho picked value halfway between Copernicus and Ptolemy

1,150 Earth Radius

1620 Kepler chose value 3,600 Earth Radius

1672 Richer & Cassini

measured parallax of Mars 21,000 Earth Radius, or 140,000,000 km

Method 1 – a smarter(?) guess

• Measure the apparent size of a planet with a telescope

• Assume a physical size of the planet

• Distance to the planet can be obtained from the ratio of physical size to the apparent angular size

It is practically accessible, but theoretically no better than pure guess

Method 2 – triangulation (parallax)

• If a planet is observed simultaneously by two observers separated by large distances, then the apparent position of the planet among the background stars would be slightly different.

• If we know the separation of the two observers, the distance to the planet can be calculated.

• Difficulties: measure of the separation, the longitude problem, small angle, synchronization of the clocks

It is prefect in theory, but difficult to execute 32

哈雷 Edmond Halley (1656 – 1742)

St Helena island

• observed Transit of Mercury in 1677

Parallax 視差

not to scale

Two pictures of the transit of Venus were taken simultaneously from Essen in Germany and Uis in Namibia on 8 June 2004.

B 比 A 早見凌始

但 A 比 B 早見凌終

A的時間短於B的時間

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 in making 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 immortal fame and glory.

Map of the Solar System, Atlas Coelestis of Johann Doppelmayr. Published in 1742.

The red dots represent expeditions of 1761 and 1769. Location: Expedition leader, Nationality 1 = Cape of Good Hope : Mason & Dixon, British (1761) 2 = St. Helena : Maskelyne, French (1761) 3 = Rodrigues Island : Pingré, French (1761) 4 = Tobolsk, Russia : Chappe, French (1761) 5 = St. John’s, Newfoundland : Winthrop, British (1761) 6 = Tahiti : Cook, British (1769) 7 = Pondicherry, India : Le Gentil, French (1769) 8 = Cabo San Lucas, Mexico : Chappe, French (1769) 9 = North Cape, Norway : Bayley, British (1769) 10 = Haiti : Pingré, French (1769) 11 = Hudson Bay, Canada : Dymond, British (1769)

經度問題

Sketch of the 1761 transit as seen by Nicholas Ypey.

1 AU = ?

When Who How 1 AU =

3rd c BCE Aristarchos geometry 1,200 Earth Radius

2nd c CE Ptolemy " " 1,160 Earth Radius

1540 Copernicus " " 1,142 Earth Radius

1600 Tycho picked value halfway between Copernicus and Ptolemy

1,150 Earth Radius

1620 Kepler chose value 3,600 Earth Radius

1672 Richer & Cassini

measured parallax of Mars 21,000 Earth Radius, or 140,000,000 km

1761 James Short

Transit of Venus 125.3 -154.8 million km

Captain Cook

Samuel Dunn (d. 1794) "A Determination of the exact Moments of Time when the Planet Venus was at external and internal contace with the Sun's Limb…,". Philosophical transactions of the Royal Society of London London: Lockyer Davis, 1771. Volume LX (1770)

1 AU = ?

When Who How 1 AU =

3rd c BCE Aristarchos geometry 1,200 Earth Radius

2nd c CE Ptolemy " " 1,160 Earth Radius

1540 Copernicus " " 1,142 Earth Radius

1600 Tycho picked value halfway between Copernicus and Ptolemy

1,150 Earth Radius

1620 Kepler chose value 3,600 Earth Radius

1672 Richer & Cassini

measured parallax of Mars 21,000 Earth Radius, or 140,000,000 km

1761 James Short Transit of Venus 125.3 -154.8 million km

1769 Richard Proctor

Transit of Venus 148.1 – 154.8 million km

1822 Johann Encke Reanalysis the data of Transit of

Venus 153,300,000 km

A new size of the solar system

• From the transit of Venus on June 3, 1769, the AU was measured to 10% accuracy.

• The size of the solar system turned out to be 100 times larger than Ptolemy’s estimate.

• Once the absolute scale (AU) is fixed, then the size and distances to the planets can be determined.

• The physical size of the solar system is finally known.

Estimates of the size of Earth's orbit, A.D. 100 - 1769

Coming of Age in the Milky Way, Timothy Ferris

1 AU = 149,598,000 kilometers

The blue dots represent expeditions of 1874 and 1882. Location: Sponsoring nations 1 = Vladivostok, Russia : United States, Russia (1874) 2 = Nagasaki, Japan : United States (1874) 3 = Beijing, China : United States, Germany, Russia, France (1874) 4 = Kerguelen Island : United States, Britain, Germany (1874) 5 = Tasmania : United States (1874) 6 = New Zealand : United States (1874, 1882), Britain (1874) 7 = Chatham Island : United States (1874) 8 = Auckland Islands : Germany (1874) 9 = Mauritius : Britain, Germany (1874) 10 = Isfahan, Iran : Germany, Russia (1874) 11 = Cairo, Egypt : Britain, Russia (1874) 12 = Hawai’i : Britain (1874)

13 = Rodrigues Island : Britain (1874) 14 = St. Paul’s Island : France (1874) 15 = Campbell Island : France (1874) 16 = Yokohama, Japan : France, Mexico (1874) 17 = Calcutta, India : Italy (1874) 18 = Tashkent, Uzbekistan : Russia (1874) 19 = Reunion Island : Netherlands (1874) 20 = South Africa : United States, Britain (1882) 21 = Santa Cruz, Argentina : United States (1882) 22 = Santiago, Chile : United States (1882) 23 = Algeria : France (1882) 24 = South Georgia : Germany (1882)

1874 北京 - James Craig Watson

1 AU = ?

When Who How 1 AU =

3rd c BCE Aristarchos geometry 1,200 Earth Radius

2nd c CE Ptolemy " " 1,160 Earth Radius

1540 Copernicus " " 1,142 Earth Radius

1600 Tycho picked value halfway between Copernicus and Ptolemy

1,150 Earth Radius

1620 Kepler chose value 3,600 Earth Radius

1672 Richer & Cassini

measured parallax of Mars 21,000 Earth Radius, or 140,000,000 km

1761 James Short Transit of Venus 125.3 -154.8 million km

1769 Richard Proctor

Transit of Venus 148.1 – 154.8 million km

1822 Johann Encke Reanalysis the data of Transit of

Venus 153,300,000 km

1874 David Todd Transit of Venus 148,098,000 km

1. Observing the different apparent paths of Venus across the face of the Sun seen from different widely spaced latitudes

2. Measuring the rate (angular velocity) at which Venus crosses the face of the Sun. The rate is the vector sum of the orbital angular velocity of Venus and the Earth and the angular velocity of the observing site due to the Earth’s daily rotation.

3. Comparing the absolute times of Venus’s contact with the Sun’s limb, seen from different places on Earth (Delisle’s method).

4. Comparing the total time for Venus to cross the Sun as seen from different latitudes, which depends on both the curvature of the Sun’s limb and the distance moved by the observer due to the Earth’s rotation (Halley’s method).

4 ways of calibrating AU using ToV

警告： 太陽觀測活動必須注意安全

不正確觀測太陽會導致永久失明

智能手機 計時 apps

5月21日日環食 香港可見 : 日出至 07:16 環食: 06:07 – 06:10

Two coming historical events

凌日階段 時間 太陽方向/方位角/仰角

日出 5時37分 東北偏東/065°/0°

Ⅰ 凌始外切 6時11分 東北偏東/068°/6°

Ⅱ 凌始內切 6時29分 東北偏東/069°/10°

凌甚 9時31分 西北偏西/081°/51°

Ⅲ 凌終內切 12時31分 西北偏西/278°/88°

Ⅳ 凌終外切 12時48分 西北偏西/274°/84°

2012年6月6日 金星凌日

不按比例

注意選擇適當的觀測地點

講座系列

第一講：金星凌日的科學與歷史 日期：2012年5月13日(星期日) 講者：張師良先生（香港大學理學院科學導師）

時間：下午3時-4時30分 地點：香港太空館演講廳

第二講：金星凌日及日環食現象及觀測 日期：2012年5月20日(星期日) 講者：余惠俊先生（香港天文學會外務副會長）

第三講：金星 日期：2012年5月27日(星期日) 講者：張師良先生（香港大學理學院科學導師）

第四講：太陽系外的凌日現象 日期：2012年6月2日(星期六) 講者：李文愷博士（香港大學物理系副教授）

6月6日觀測活動 • 尖沙咀星光大道 • 06:00 - 13:00

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