2. 太白金星
Venus
Credit: Juan Manuel Pérez Rayego

3. 全天第三亮
的天體
Fred Espenak
Doug Zubenel (TWAN)

4. 晨星/昏星
大距
Venus Feb - Sep 2010
Cenk E. Tezel & Tunc Tezel

5. 內行星 vs 外行星
上合
合 西大距
衝
東大距 下合

6. 罕有的金星凌日
• 1631 December 7
• 1639 December 4
121.5 years
• 1761 June 6
• 1769 June 4
105.5 years
• 1874 December 9
• 1882 December 6
121.5 years
• 2004 June 8
• 2012 June 6
105.5 years
• 2117 December 11
Last chance in your life!

7. 金星與
地球的
軌道
3.4° 夾角
軌道周期: 地球與金星
金星 224日 的會合周期:
地球 365日 584日 (1.6年)

8. Paper Plate Education
http://analyzer.depaul.edu/paperplate/

9. 2012年6月6日 金星凌日
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°
不按比例
凌甚 9時31分 西北偏西/081°/51°
注意選擇適當的觀測地點 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°

11. 哥白尼 Nicolaus Copernicus (1473-1543)
天體運行論, 1543
De revolutionibus orbium coelestium
(On the Revolutions of the Celestial Spheres)

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

17. 第谷
Tycho Brahe
(1546-1601)

19. 開普勒 Johannes Kepler (1571-1630)

20. 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
a
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

21. The Rudolphine Tables by Johannes Kepler, 1627

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

23. 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

24. Pierre Gassendi (1592-1655)
• French observed Transit of Mercury on Nov 7, 1631
• name "Aurora Borealis"

25. Angular size VS real size
a much bigger solar system!

26. Jeremiah Horrocks (1618 - 1641)
• British
• predicted and
observed the transit of
Venus on Dec 4, 1639

27. The only 2 people
saw the Transit of
Venus in 1639
Jeremiah Horrocks William Crabtree

29. Cosmotheoros by Christiaan Huygens, 1698

30. 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 1,150 Earth Radius
Copernicus and Ptolemy
1620 Kepler chose value 3,600 Earth Radius
1672 Richer & measured parallax of Mars 21,000 Earth Radius, or
Cassini 140,000,000 km

31. 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

32. 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

33. 哈雷 Edmond Halley
(1656 – 1742)
• observed Transit of Mercury in 1677
St Helena island

34. not to scale
Parallax
視差

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

37. A的時間短於B的時間
B 比 A 早見凌始
但 A 比 B 早見凌終

38. 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.

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

40. 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)

41. 經度問題

42. Sketch of the 1761 transit as seen by Nicholas Ypey.

43. 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 1,150 Earth Radius
Copernicus and Ptolemy
1620 Kepler chose value 3,600 Earth Radius
1672 Richer & measured parallax of Mars 21,000 Earth Radius, or
Cassini 140,000,000 km
James
1761 Transit of Venus 125.3 -154.8 million km
Short

44. Captain Cook

48. 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)

49. 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 1,150 Earth Radius
Copernicus and Ptolemy
1620 Kepler chose value 3,600 Earth Radius
1672 Richer & measured parallax of Mars 21,000 Earth Radius, or
Cassini 140,000,000 km
1761 James Short Transit of Venus 125.3 -154.8 million km
Richard
1769 Transit of Venus 148.1 – 154.8 million km
Proctor
Reanalysis the data of Transit of
1822 Johann Encke 153,300,000 km
Venus

50. 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,
1 AU = 149,598,000 kilometers A.D. 100 - 1769
Coming of Age in the Milky Way, Timothy Ferris

51. The blue dots represent expeditions of 1874 and 1882.
Location: Sponsoring nations
1 = Vladivostok, Russia : United States, Russia (1874) 13 = Rodrigues Island : Britain (1874)
2 = Nagasaki, Japan : United States (1874) 14 = St. Paul’s Island : France (1874)
3 = Beijing, China : United States, Germany, Russia, France (1874) 15 = Campbell Island : France (1874)
4 = Kerguelen Island : United States, Britain, Germany (1874) 16 = Yokohama, Japan : France, Mexico (1874)
5 = Tasmania : United States (1874) 17 = Calcutta, India : Italy (1874)
6 = New Zealand : United States (1874, 1882), Britain (1874) 18 = Tashkent, Uzbekistan : Russia (1874)
7 = Chatham Island : United States (1874) 19 = Reunion Island : Netherlands (1874)
8 = Auckland Islands : Germany (1874) 20 = South Africa : United States, Britain (1882)
9 = Mauritius : Britain, Germany (1874) 21 = Santa Cruz, Argentina : United States (1882)
10 = Isfahan, Iran : Germany, Russia (1874) 22 = Santiago, Chile : United States (1882)
11 = Cairo, Egypt : Britain, Russia (1874) 23 = Algeria : France (1882)
12 = Hawai’i : Britain (1874) 24 = South Georgia : Germany (1882)

56. 1874 北京 - James Craig Watson

64. 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 1,150 Earth Radius
Copernicus and Ptolemy
1620 Kepler chose value 3,600 Earth Radius
1672 Richer & measured parallax of Mars 21,000 Earth Radius, or
Cassini 140,000,000 km
1761 James Short Transit of Venus 125.3 -154.8 million km
Richard
1769 Transit of Venus 148.1 – 154.8 million km
Proctor
Reanalysis the data of Transit of
1822 Johann Encke 153,300,000 km
Venus
1874 David Todd Transit of Venus 148,098,000 km

67. 4 ways of calibrating AU using ToV
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).

69. 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

70. 智能手機 計時 apps

71. Two coming historical events
5月21日日環食
香港可見 : 日出至 07:16
環食: 06:07 – 06:10

72. 2012年6月6日 金星凌日
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°
不按比例
凌甚 9時31分 西北偏西/081°/51°
注意選擇適當的觀測地點 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°

73. 講座系列 時間：下午3時-4時30分 地點：香港太空館演講廳
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）
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）

74. 6月6日觀測活動
• 尖沙咀星光大道
• 06:00 - 13:00
• 小型觀測站在網頁公佈
• 網上直播
www.facebook.com/transitofvenushk
transitofvenus.hk
hk.space.museum
roadshow.science.hku.hk