Venus is an inner planet of the Solar System. Whenever it comes exactly between the Earth and the Sun, its silhouette will be found passing the Sun's disc slowly. This phenomenon is called the transit of Venus. Although Venus is bigger than Mercury and its transit is more spectacular than Mercury's, it is much rarer. Transits of Venus take place in pairs separated by over a century. The last ones occurred in 1874 and 1882. The next transits of Venus will occur on 8 June, 2004, and 6 June, 2012.
Transit of Venus 2004 in Retrospect
In the afternoon of 8 Jun 2004, Transit of Venus happened over Hong Kong sky. About 3,000 citizens visited Hong Kong Space Museum and witnessed this rare celestial event through telescopes. They were all in high spirits despite of the occasional clouds.
For those who could not see the transit by themselves, many of them chose to watch the webcast jointly provided by the Museum and the Hong Kong Observatory. The total hit rate exceeded 1.2 million.
The 2004 transit gave us the opportunity to study the "Black Drop" effect which puzzled astronomers for more than 200 years. When Venus was close to the Sun's limb, its silhouette seemed to drip from the Sun's limb and became a black drop. According to earth-bound and space-bound observations, the black drop is confirmed to be a mere optical illusion caused by the Earth's atmospheric turbulence and insufficient resolution of small telescopes. It has nothing to do with the Venusian atmosphere.
Transit of Venus
Activities in Space Museum
Transit of Venus on 8 June 2004
Eye injury caused by the Sun's radiation
Intensive ultra-violet radiation, visible light and infrared radiation can be damaging to our eyes. Ultra-violet light is known to contribute to the accelerated aging of the outer layers of the eye and the development of cataract. While intense visible light damages the eyes' photosensitive cells, thereby impairing their photo-sensory functions, infrared radiation literally cooks the sensitive tissues in the eyeball, and can precipitate the formation of small blind areas in the retina in extreme cases.
Though the sun may look dim, especially through filters, indicating that most of the visible light is blocked out, the invisible ultra-violet and infrared radiation can still reach our eyes unabated. As pain receptors are absent in our retinas, we may not feel immediate pain while our eyes are being injured. Worse still, symptoms of visual impairment will begin to appear hours after irreparable damage has already been done.
A solar filter can be regarded as "safe" if it is able to filter at least 99.9997% of visible light and most of the infrared and ultra-violet radiation.
Do not look at the Sun directly;
Do not look at the Sun through smoked glass, exposed films, ink or sunglasses; and
Do not look at the Sun continuously for over a minute. Let the eyes have enough rest from time to time.