Moongold
"The Air was perfectly clear, so that we had every advantage we could desire in Observing the whole of the passage of the planet Venus over the Suns disk: we very distinctly saw an atmosphere or dusky shade round the body of the Planet which very much disturbed the times of the contacts particularly the two internal ones."
- Diary entry by Captain James Cook, Tahiti, 1769
Come Tuesday afternoon, if it is fine, we will know what Captain Cook was talking about when he was describing the transit of Venus. For Australians, the transit will have added poignancy, as it was responsible for the timing of the nation's settling.
"The transit of Venus is one of the most celebrated phenomena in astronomy and has been described as a magnificent rendezvous between the planet of love and the bright orb of the sun," said Professor Graeme White of James Cook University. "Nobody alive today has witnessed the spectacle, which last occurred 122 years ago."
In the 18th century, it was Venus, not Mars, that grabbed everyone's attention. Then, the key astronomical question was not the whereabouts of extraterrestrial life, but how far the sun is from Earth.
In 1716, astronomer Edmund Halley realised that timing the Venus transit from places around the globe could, by simple geometry, lead to a precise estimation of the Earth-sun distance. As Venus and Mercury are the only planets that orbit closer to the sun than the Earth, they alone can "transit" - pass directly between us and the sun and appear as a black silhouette.
But unlike an eclipse, a transit is visible only if you have the right equipment. As Venus blocks just 0.1 per cent of the sun's light, it is lost in the glare and cannot be seen with the naked eye.
Astronomer Johannes Kepler first predicted there would be a Venus transit in 1631. Unfortunately he died in 1630. But in 1639, English astronomer Jeremiah Horrocks realised upon studying Kepler's tables that another transit was imminent. He was awestruck by the event.
"Nobody alive today has witnessed the spectacle, which last occurred 122 years ago."
- Professor Graeme White
In the transits of 1761 and 1769, European governments sent explorers to far-flung places of the globe to observe, and accurately time, the event. Captain Cook was sent to Tahiti in 1769. After the transit, Cook opened sealed secret orders from the navy asking him to "search between Tahiti and New Zealand for a continent". The following year, Cook found and mapped the east coast of the Great Southern Land and prepared the way for the First Fleet's arrival in 1788. Cook's secondary mission of discovery proved more successful than the Venus observations. As described in his diary, the times of contact between Venus and the sun were hard to pinpoint and his results were not accurate enough to calculate the sun-Earth distance (later found to be 150 million kilometres).
On average, Venus passes between Earth and the sun every 18 months. So why was the last transit in 1882? And why will the next one be in 2012? The answer is that Venus's orbital path around the sun is tilted. Most of Venus passes above or below the sun. For a transit, these orbital paths must line up so Venus passes directly between Earth and the sun.
Due to Venus's orbit tilt and the length of the Venusian year (which equals 224.7 Earth days) transits follow an odd pattern. Every 121 years there is a transit, another one eight years later, which is followed by another 121-year gap.
Tuesday's transit should be visible in Melbourne from 3.08pm until sunset at 5.07pm. To observe it, you will need specialist eclipse eyewear, a sun filter attached to a telescope, or you will have to project the image from binoculars or a telescope onto cardboard. Viewings will be held by Scienceworks, the Old Melbourne Observatory in the Royal Botanic Gardens, the Astronomical Society of Victoria (roof car park, Victoria Gardens shopping centre, Richmond) and the Astronomical Society of Melbourne (bookings: 0412 318 125.) James Cook University will have a webcast: www.jcu.edu.au
I live very close to the Royal Astronomical Society and have booked to attend the viewing as I'm taking some days off work. I'm tremendously excited!
Moongold
·
- Diary entry by Captain James Cook, Tahiti, 1769
Come Tuesday afternoon, if it is fine, we will know what Captain Cook was talking about when he was describing the transit of Venus. For Australians, the transit will have added poignancy, as it was responsible for the timing of the nation's settling.
"The transit of Venus is one of the most celebrated phenomena in astronomy and has been described as a magnificent rendezvous between the planet of love and the bright orb of the sun," said Professor Graeme White of James Cook University. "Nobody alive today has witnessed the spectacle, which last occurred 122 years ago."
In the 18th century, it was Venus, not Mars, that grabbed everyone's attention. Then, the key astronomical question was not the whereabouts of extraterrestrial life, but how far the sun is from Earth.
In 1716, astronomer Edmund Halley realised that timing the Venus transit from places around the globe could, by simple geometry, lead to a precise estimation of the Earth-sun distance. As Venus and Mercury are the only planets that orbit closer to the sun than the Earth, they alone can "transit" - pass directly between us and the sun and appear as a black silhouette.
But unlike an eclipse, a transit is visible only if you have the right equipment. As Venus blocks just 0.1 per cent of the sun's light, it is lost in the glare and cannot be seen with the naked eye.
Astronomer Johannes Kepler first predicted there would be a Venus transit in 1631. Unfortunately he died in 1630. But in 1639, English astronomer Jeremiah Horrocks realised upon studying Kepler's tables that another transit was imminent. He was awestruck by the event.
"Nobody alive today has witnessed the spectacle, which last occurred 122 years ago."
- Professor Graeme White
In the transits of 1761 and 1769, European governments sent explorers to far-flung places of the globe to observe, and accurately time, the event. Captain Cook was sent to Tahiti in 1769. After the transit, Cook opened sealed secret orders from the navy asking him to "search between Tahiti and New Zealand for a continent". The following year, Cook found and mapped the east coast of the Great Southern Land and prepared the way for the First Fleet's arrival in 1788. Cook's secondary mission of discovery proved more successful than the Venus observations. As described in his diary, the times of contact between Venus and the sun were hard to pinpoint and his results were not accurate enough to calculate the sun-Earth distance (later found to be 150 million kilometres).
On average, Venus passes between Earth and the sun every 18 months. So why was the last transit in 1882? And why will the next one be in 2012? The answer is that Venus's orbital path around the sun is tilted. Most of Venus passes above or below the sun. For a transit, these orbital paths must line up so Venus passes directly between Earth and the sun.
Due to Venus's orbit tilt and the length of the Venusian year (which equals 224.7 Earth days) transits follow an odd pattern. Every 121 years there is a transit, another one eight years later, which is followed by another 121-year gap.
Tuesday's transit should be visible in Melbourne from 3.08pm until sunset at 5.07pm. To observe it, you will need specialist eclipse eyewear, a sun filter attached to a telescope, or you will have to project the image from binoculars or a telescope onto cardboard. Viewings will be held by Scienceworks, the Old Melbourne Observatory in the Royal Botanic Gardens, the Astronomical Society of Victoria (roof car park, Victoria Gardens shopping centre, Richmond) and the Astronomical Society of Melbourne (bookings: 0412 318 125.) James Cook University will have a webcast: www.jcu.edu.au
I live very close to the Royal Astronomical Society and have booked to attend the viewing as I'm taking some days off work. I'm tremendously excited!
Moongold
·
