by Knut Jørgen Røed Ødegaard
On June 8, 2004 we will experience the most extraordinary and
important celestial phenomenon in our life time. For more than 6 hours
the planet Venus will be visible in front of the Sun. No living
persons anywhere on the Earth have witnessed this before! Actually,
this will be the first time in history that everyone can follow the
transit with their own eyes using eclipse glasses. The phenomenon will help
scientists to find life on remote planets.
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Transit of Venus as it will be seen from Norway on June 8, 2004. In 6 hours Venus will cross
the solar disk.
Illustration: Astronomy.no
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Since the planets Mercury and Venus orbit the Sun inside Earths orbit,
they may from time to time pass between the Sun and Earth. On very rare
occasions they may even line up with the Sun and the Earth so that
they transit the Sun when observed from the Earth. The last time this
happened was May 7, 2003, when Mercury crossed the solar disk.
Transits of Venus are much rarer. The last time it happened was in 1882
and there are no living people on the Earth har ever witnessed Venus in
front of the Sun! There are only a few rather poor images from the 1882 event.
Only 4 transits of Venus have been observed by humans.
HISTORIC VIEW
Venus is so much larger than Mercury that it can easily be seen with the
naked eye as a small black dot on the solar disk if eclipse glasses are
used. On earlier transits of Venus such equipment has not been available.
The transit on June 8, 2004 will be historic because it is the first
one than everyone can study with their own eyes!
More about observations
of the phenomenon.
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The transit of Venus in 182 photographed from US Naval Observatory.
Photo: US Naval Observatory
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HOW LARGE IS THE WORLD?
Humans have always wondered about the cosmic distances and how far stars
and planets really are. With the invention of the telescope i 1610
scientific methods could be applied to solve the question. But is a
quite hard problem. The relative distances between the planets and the
Earth were determined, but the distance scale was still unknown.
It soon turned out that the rare transits gave unique opportunities to
measure the distances. The extremely rare transits of Venus are most
useful. For the transit i 1769 expeditions were sent to several locations
around the globe. The transits start at slightly different times on
different locations. The reason is that the observers see Venus in a slightly
different angle. Since the sixe of the Earth was known, cosmic distances
could be inferred from the transit times measured on remote locations.
The most exciting expeditons were probably that of Captain James Cook to Tahiti and
an expedition to Vardø in Northern Norway. Christian VII, king of Denmark and Norway
invited the royal Austrian astronomer Miksa Hell to Vardø. After spending a very rough
winter in the far north he successfully observed the transit i June 1769.
He found the distance to the Sun to be 151.2 million km, very close to the modern
value of 149.6 million km. The results made Hell rather famous astronomer.
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This is one of extremely few images ever taken of a Venus in transit.
It was taken in 1882 by students at Vassar College.
Photo: Vassar College
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The results gave the basis of all later studies of the Universe! Without this
transit of Venus it would have taken more than 100 years to find the
the distance scale in the Solar System.
The expedition of James Cook also discovered Australia and New Zealand.
Transits of Venus have therefore made both the Earth and the Universe much
larger for us humans.
LIFE ON OTHER PLANETS? VENUS MAY GIVE THE ANSWER!
When Venus crosses the solar disk, it is the first time in modern times that
a planet with an atmosphere do that. This is a truly unique opportunity to study
such transits. It will tell us how and what to look for when exoplanets similar to
the Earth transits their star.
Since 1995 about 110 exoplanets have been discovered. They are not observed
directly and they are all giant gas planets without life. Their gravitational
pull on their star reveal their existence. The only way to detect planets
similar to the Earth, that can support life, is by studying the rare occasions
when they transit their star. Only a smal percentage of them do that.
A small fraction of the stellar light is blocked - this can be observed
from Earth. But some light moves through the atmosphere of the planet and
get "fingerprints" of the chemical substances in the atmosphere.
If we in this way find oxygen (or rather ozone) and water, it is a
certain evidence for life!!
So far only three exoplanets have been observed while transiting their
star and they were all too hot for life. The transit of Venus will be
used for training: What should we look for?
Several other research projects will also be conducted during the transit.
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