Utrecht, june 8th 2004, 07 h 19 m : a black dot passes in front of the sun
I : first contact at 07 h 19 mII: seccond contact at 07 h 39 m
III: third contact at 13 h 03 mIV : fourth contact at 13 h 23 m
A transit of Venus: a mini solar eclipse
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20042012
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8 8 8 8 8121 ½ 121 ½ 105 ½ 105 ½
Regularity in the occurance of transits of Venus
No transit
Transit!
But the orbit of Venus is tilted slightly with respect to orbit of the earth around the sun (3,4o).
Usually when Venus overtakes the earth there is no exact alignment
Exact alignment: very rare!
When Venus meets the earth
William Crabtree (friend of Horrocks) is the seccond person to observe the 1639 transit
“I beseech you, therefore, with all my strength, to attend to it diligently with a telescope and to make whatever observation
you can….” Horrocks, in a letter to Crabtree
A
A
BB
The path of Venus acros the sun by observers A and B as seen from the earth
Halley (1656-1742) proposed a method to measure the ‘immense distance to the sun’ by international coordinated observations during the transit of 1761.
The unfortunate adventures of Guillaume-Joseph-Hyacinthe-Jean-Baptiste Gentil de la Galaisière (Le Gentil)
maart 1760
juli 1760
mei 1761
6 juni 1761
mrt 1768
mrt 1770
okt 1771
aug 1766
The unfortunate adventures of Guillaume-Joseph-Hyacinthe-Jean-Baptiste Gentil de la Galaisière (Le Gentil)
Members of the Dutch expedition in 1874 in front of their accommodation in St. Denis, Réunion
Observation camp of the Dutch expedition
1874: Dutch participation !
VENUS
Distance to the sun: 108 million km 0,72 AU
Diameter: 12.104 km (0,95 x earth)
Massa: 4,7 x 1024 kg (0,80 x earth)
Temperature (surface): 490 °C
Pressure (surface): 90 atmosphere
The atmosphere is is composed mostly of carbon dioxide. There are several layers of clouds, many kilometers thick, composed of sulfuric acid.