Venus Transit

History

    First attempt to watch Venus was made by French astronomer Gassendi in the year 1631. He had a bad luck because the phenomenon was almost impossible to watch from Europe. His misfortune was almost unbelievable because the picture of Venus leaving the Sun circle was visible in Italy, Austria, Bohemia, Germany and Denmark. Unfortunately, Gassendi tried to watch it from Paris…
    First attempt to watch Venus was made by French astronomer Gassendi in the year 1631. He had a bad luck because the phenomenon was almost impossible to watch from Europe. His misfortune was almost unbelievable because the picture of Venus leaving the Sun circle was visible in Italy, Austria, Bohemia, Germany and Denmark. Unfortunately, Gassendi tried to watch it from Paris…Astronomers nearly missed also the second chance. Johanes Kepler made a wrong prediction - Rudolphinian charts, which he made to predict the planet movements and was his last great work before his death, told him that next transit would not occur before 6th June 1761. Luckily, only one month before the transit, marvelous English astronomer Jeremiah Horrocks found out that the next transit would be on 4th December 1639!
    Jeremiah Horrocks and his friend William Crabtree saw, only half an hour before dusk, something that no one before them had chance to see. Horrocks himself described it this way: "Clouds were scattered by something like God's bless and I could start my observation again. Then I saw the most beautiful view, the object of my wishes, unusually clear and perfectly circle-shaped. It was without a doubt really the shadow of the planet, which I immediately started to watch." Let's add that Horrocks almost missed this event - he had to interrupt his afternoon observation because, as a puritan and a priest, he had to serve a service in a church near Liverpool. His friend Crabtree was observing from a place distant about fifty kilometers, but he has no chance to see Venus because of clouds.
    This was the end of the first lap. For next Venus transit astronomers had to wait for another 122 years.

Phase II - 1761 and 1769

    So, what happned then? Venus transits didn't fall into oblivion, because Edmond Halley suggested that this phenomenon could be used to calculate the dimensions of the Solar system. How? Very simply.
    Thanks to Kepler's rules, astronomers knew the proportions between the distances of the planets. For example, Venus was roughly in 70% of Earth's distance to the Sun and Mars rotated roughly in 1 and half of this distance. But the astronomers didn't know the distances in absolute units, let's say in kilometers or miles. They needed some astronomical unit. To find it, they would need to know at least one parallax of some planet in the Solar system and that was above the abilities of their devices. Edmond Halley suggested astronomers to use 4 contacts of Venus and the Sun (Outer and iner contact on both sides). The planet was, when observed from another places on Earth, visible on another part of the Sun discus so the times of contacts were different. These times were then used for calculation.
    Obtained information wasn't much useful for these calculations after all, but the observers found out two interesting things. The first was a pale halo, which had appeared around Venus even before the first contact occurred. The second was the phenomenon of the "Black droplet" which appeared when a whole planet was in front of the Sun. The planet's circle stretched a bit into a shape of the droplet. This first thing is conected with the density Venus's atmosphere that disperses sunlight. The second thing, the black droplet is formed thanks to diffractions in telescope and thanks to a dazzle of the observer.
    Next chance to see Venus Transit occurred on 3rd and 4th June 1769. English king George III. organized two big expeditions. One was sent into the Hudson's Bay and the second, under the lead of James Cook, to Tahiti. Let's add that main task wasn't observing the Venus. It was a camouflage for searching for new colonies and lands. These lands were terra incognita (uncharted lands) and the royal scholars rightly thought that some new continent could be here. In England, even George III observed this phenomenon on Greenwich observatory.
    This expedition was a great success for James Cook. His observations were made from the place that is even today called Venus Point. This started Cook's carrier of a sailor, which ended with his murder on Hawaii. After Venus Transit, he and his ship, Endeavor, sailed through the Pacific ocean and on 9th November 1769, Cook watched transit of Mercury and then, as a first man from Europe gauged the size of Australia.

Phase III: 1874 and 1882

    Whilst in 18th century the main hunters of Venus were the European states, this time the initiative was taken by the United States of America. Swift evolution of technologies, especially photography and precise chronometers, promised more precise results than before. It was quite a paradox - astronomers knew quite precise distances of about twenty nearest stars, but the Astronomical unit was still quite inaccurate. "Finding this unit is the greatest astronomical task of this century", wrote Simon Newcomb in year 1880.
    On 9th December 1874, a Venus transit happned, astronomers went back home and from their observations they calculated that the distance between the Sun and Earth is between 148,1 and 149,4 million kilometers. That was almost fifteen-time greater error than they had expected. A great campaign resulted in almost nothing new.
    No wonder that next hunt, on 6th December 1882, the astronomers were quite reserved and restrained. They observed the transit from many places on Earth but again the expectations were small. But the phenomenon didn't lose its symbolism as one of the Simon Newcomb's diary entries from 6th December documents: 'On our land, we left two metal pillars, which we used for our photographic devices, firmly embedded in the ground. Maybe they will stay here until next transit in 2004. I don't know, but I can't resist a sentimental wish - That in 2004 someone will watch the transit from the same place as we did and the pillars will be still useable for telescopes.'

2004 Designed by Melcolm