1631 Transit of Venus
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The Wayback Machine - https://web.archive.org/web/20061001062918/http://www.nao.rl.ac.uk/nao/transit/V_1631/
Background
The French astronomer Gassendi planned to observe this transit from Paris
using predictions from Kepler's "Rudolphine Tables" of planetary motion
published in 1627. Unfortunately, he missed the transit due to the fact that
the tables were not accurate enough to show that the transit actually took
place during the early hours of December 7
th
while the Sun was
still below the horizon in western Europe and in particular Paris.
Visibility
Venus crossed the disc of the Sun on 1631 December 7
th
. The map
above shows the global visibility of the event. The transit could be seen in
its entirety from Australasia, southern and central Asia, the Indian Ocean and
eastern parts of Africa. The Sun set while the transit was in progress in the
grey areas encompassing the central Pacific Ocean and parts of north-eastern
Asia. The Sun rose while the transit was in in progress in the grey areas
taking in Africa except the eastern part, south-eastern Europe, eastern Russia
and the Middle East. The yellow lines on the diagram show the position of the
terminator, where the Sun is either rising or setting, at the key phases of
the transit.
Geocentric Circumstances
The geocentric circumstances of the transit are shown in the diagram to the
right. During the transit, the diameter of the Sun was 1949.9 arcseconds and
that of Venus was 63.2 arcseconds. In other words, the diameter of Venus was
0.03 that of the Sun, making it look like a rapidly moving sunspot. The whole
transit lasted just under three hours.
All timings are given in Universal Time (UT).
The Transit as seen from Jerusalem
Local time in Jerusalem is 3 hours ahead of Universal Time.
Despite the fact that this transit was probably unobserved, Jerusalem
has been chosen as a possible observing site to demonstrate how the transit
might have been observed inadvertently during sunrise when atmospheric
extinction or low cloud would have made the Sun's disc easier to observe. The
progress of the transit as seen from Jerusalem is summarized in the diagram
below. The left-hand panel shows the movement of the Venus across the solar
disc. The top of the diagram points to the zenith, the point directly overhead.
The position of Venus is marked every UT hour. The right-hand panel shows
the movement of the Sun in the sky during the transit.
The transit started with exterior ingress just before the start of morning
civil twilight at 03
h
53
m
(UT) as seen from Jerusalem.
The Sun rose in the south-eastern sky at 04
h
27
m
(UT)
and interior ingress occurred at 04
h
47
m
when the Sun
was only 3° above the horizon. Venus had taken nearly an hour to cross
the limb of the Sun. Approximately three quarters of an hour later, Venus
reached its minimum separation of 929.2 arcseconds from the centre of the
solar disc at 05
h
27
m
when the Sun was 10° above the
horizon. Venus started to cross the limb of the Sun for the second time at
06
h
06
m
(UT) and the transit ended at
07
h
00
m
(UT) when the Sun had reached nearly 25°
above the horizon.
Local Circumstances
Summary plots like the one shown above and animations showing the motion
of Venus relative to the Sun as seen by someone observing the transit through
appropriate eye protection are available for several locations worldwide. The
summary gif files are ~18Kb and the animations are ~200Kb. To view the
animations properly, it may be better to download the animations and view
them locally.