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Venus and Transit of Venus Fact File
3021/ Venus is named
after the Roman goddess of love and is about the same size
as the Earth.
3022/ Despite being about
the same size as the Earth it is not quite so pleasant! Venus
has no oceans and is surrounded by a heavy carbon monoxide
atmosphere. It's atmospheric pressure is 92 times that of
the Earth's at sea level.
3023/ Venus may well
once have had water like Earth does, but because of the scorching
surface temperature of 482 degrees C (900 degrees F). Any
sign of it has long ago evaporated.
3024/ Venus is the second
closest planet to the Sun, and the sixth largest overall.
3025/ The first spacecraft
to visit Venus was Mariner 2 in 1962. It was subsequently
visited by many others (more than 20 in all). Including Pioneer
Venus and the Soviet Venera 7 - the first spacecraft to land
on another planet - and Venera 9 which returned the first
photographs of the surface.
3026/ On June 8 2004,
Venus passed directly between the Earth and the Sun, appearing
as a large black dot travelling across the Sun's disk. This
event is known as a "transit
of Venus" and is very rare: the last one was in 1882,
the next one is in 2012 but after than you'll have to wait
until 2117.
3027/ A transit of Venus
is like a solar eclipse, but instead of the Moon being in
line between the Earth and Sun it is the planet Venus. You
can hardly fail to notice a solar eclipse because the Moon,
being about the same apparent size as the Sun, blocks out
its light. Venus, on the other hand, looks very much smaller
from Earth and so you would have to be specifically observing
the Sun to see the small disc of Venus passing across its
disk.
3028/ There is some strange
mathematical sense to the years between Venusian transits.
The circumstances repeat in this manner: 8 years, 121½
years, 8 years, 105½ years.
3029/ The next transit
is on June 6, 2012 and will be visible from northwestern North
America, northern Asia, Japan, Korea, eastern China, Philippines,
eastern Australia, and New Zealand, according to NASA. Portions
of the 2012 event will be visible in parts of North America,
Asia, the Middle East, Europe and Africa.
3030/ Because the first
Venusian transit was only predicted in the 1600s, by Johannes
Kepler, only five have been recorded, in 1639, 1761, 1769
and 1874 and 1882.
3031/ The plot of Thomas
Hardy's 1883 novel "Two on a Tower" incorporates
a transit of Venus. Hardy himself visited the Royal Greenwich
Observatory prior to the 1882 transit of Venus. The English
astronomer Jermiah Horrocks, who first saw a transit of Venus,
is the basis for one of the characters.
3032/ When a transit
of Venus occurs, a second one often follows eight years later.
This is because the orbital periods of Venus (224.701 days)
and Earth (365.256 days) are in an 8 year (2922 days) resonance
with each other. In other words, in the time it takes Earth
to orbit the Sun eight times, Venus completes almost exactly
thirteen revolutions about the Sun.
3033/ A useful way to
organize the transits is by grouping them into series where
each member of a series is separated by 88,756 days or 243
years (= sum of 8 + 105.5 + 8 + 121.5 years). Thus, the transits
of 1518, 1761 and 2004 would belong to one series, while the
transits of 1639, 1882 and 2125 would belong to another series.
Such transit series are quite long-lived and may last 5,000
years or more.
3034/ The position of
the orbital nodes of Venus with respect to Earth are slowly
changing with time. Five thousand years ago, transits occurred
around May 21 and November 19. At present, the transits occur
within a day of June 7 and December 9. In about 1500 years,
the transits will occur during Earth's solstices (June 21
and December 22).
3035/ The basic "metre
stick" of astronomy is the distance between the Earth
and the Sun, appropriately called the Astronomical Unit or
just au.This can be determined by observing the transit of
a planet across the face of the Sun. Only planets inside the
Earth's orbit can manage this. Thus the transit of Venus provides
an opportunity to measure the distance to the Sun. Such a
measurement in 1639 represented the beginning of astrophysics
in England.
3036/ Kepler correctly
predicted that an ascending node transit of Venus would occur
in December 1631, but no-one observed it - due to the fact
that it occurred after sunset for most of Europe. Kepler himself
died in 1630. He not only predicted this particular transit
but also worked out that transits of Venus involve a cyclical
period of approximately 120 years.
3037/ Captain Cook’s
first voyage around the world was planned so that the 1769
transit could be observed in Tahiti. For the same transit,
King George III had an observatory specially built so that
he could conveniently view the event near London.
3038/ As seen from Earth,
only transits of the inner planets Mercury and Venus are possible.
The first transit ever observed was of the planet Mercury
in 1631 by the French astronomer Gassendi. A transit of Venus
occurred just one month later but Gassendi's attempt to observe
it failed because the transit was not visible from Europe.
In 1639, Jerimiah Horrocks and William Crabtree became the
first to witness a transit of Venus.
3039/ In 1716, Edmond
Halley published a paper describing exactly how transits could
be used to measure the Sun's distance, thereby establishing
the absolute scale of the solar system from Kepler's third
law.
3040/ Venus is the brightest
planet in our sky and can sometimes be seen with the naked
eye if you know where to look.
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