Transit of Venus vying with the Monsoons - Part 1

We have had two chances in our lifetimes to see Planet Venus traipsing across the disc of the Sun. On 8 June 2004 came the first of the pair of transits of Venus and the second, on June 6, 2012, will be the last in this century. The next time people on earth will witness the rare spectacle of Venus moving across the disc of the Sun will be in December 2117. So this event has caused a flurry among astronomers professional and amateur.

If Venus orbits the Sun in the same plane as the orbit of the Earth we would see such transits often. But since its orbit is inclined to the Earth by about 3.4 degrees, when Venus passes between the Sun and Earth every 1.6 years, it is usually a little below or a little above the line joining Earth and Sun. We only see transits on those rare occasions when the three objects are in an inferior conjunction, or a straight line with the Sun and Venus on the same side of the Earth. When Venus passes between the Sun and the Earth near the nodes a transit occurs. The points where the orbit of Venus crosses the Ecliptic are called the Nodes.

Transits of Venus take place at regular intervals, four times in 243 years, and in pairs separated by eight years. There is such a pair, then there is a span of 105.5 years without any transit then another pair separated by eight years and then a gap of 121.5 years.

The first recorded viewing of the transit was by Jeremiah Horrocks in 1639, about thirty years after the discovery of the telescope.  Since then transits have been observed in 1761, 1769, 1874, 1882 and 2004.

In order to promote the idea of viewing the celestial event, the Tamilnadu Science and Technology Centre supported by Vigyan Prasar has held awareness camps all over the country. Workshops for teachers were held in April and May each lasting three days for about 50 people selected from schools close to that area. The last of these camps was held at Anna Science Centre – Planetarium in Tiruchirapalli between 25 and 27 May 2012,  for Post-graduate teachers; Elementary education officers and Science communicators from Kerala, Puducherry and parts of southern Tamilnadu. About 65 people participated in the workshop.

Annular Solar Eclipse over China Japan and Western USA

On 20 and 21 May, some parts of China, Japan and Western United States will witness an annular solar eclipse, or eclipse of the sun. Depending where they are on the path of the eclipse on earth, people will be able to see the sun as a glowing diamond ring. Others will be able to see the sun as a crescent.

This eclipse will sweep over a width of 240-300 km track from eastern Asia, the northern Pacific ocean and western United States. The eclipse begins at sunrise over southern China at 2206 GMT and then travel to southern Japan. Residents of Tokyo can see an annular phase for about fifteen minutes starting from 2232 GMT. Then the shadow passes over the Pacific ocean over a long stretch of 7000 km in about two hours. It touches the states of Oregon and northern California by which time it will be evening as per local time in those states.
   

With the advanced technology we have now, solar eclipses can be predicted well in advance. But do you know what is an eclipse and why they occur only on special occasions. As seen from earth, an eclipse of the sun can only occur on a new moon day. This is when the moon passes between the sun and the earth. Whenever the shadow of the moon falls on the surface of the earth, those areas can view an eclipse. This is the blocking of the light from the sun, so that the sun’s disc appears partially or completely blackened.

We may think that such an eclipse can occur on every new moon day, but that is not the case. This is because the moon’s orbit around the earth is tilted at five degrees to the plane of the earth’s orbit around the sun.

Roughly twice a year there is a solar eclipse on earth. But these are not viewed each time. Mostly, the eclipses fall on remote areas or cover really small areas of the earth’s surface and so they go unviewed. At other times during an eclipse there are clouds that block the view and prevent enthusiasts from watching the celestial phenomenon.

People go to remote areas therefore to watch the eclipses when they happen. The best areas to view this eclipse of 20-21 May are said to be the desert areas of Nevada, southern Utah and northern Arizona.

The next time the earth will witness a total solar eclipse is predicted to be on 13 November 2012 over northern Australia and Southern Pacific. The next time there will be an annular eclipse over parts of India is 26 December 2019.