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Wednesday, June 6, 2012

Thousands witness the rare spectacle of 'transit of Venus across Sun'

It was the much-awaited cosmic event -- the transit of the Venus, the last for this century, that occurred this morning [6th June 2012], giving sky lovers all over the country an opportunity to witness the celestial phenomenon.  It was stated that staring at the Sun without appropriate eye protection can quickly cause serious and often permanent eye damage.  Transit of the Venus is a rare eclipse during which the planet passes between the Earth and the Sun.

Venus is the second planet from the Sun, orbiting it every 224.7 Earth days; it is so  named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky.

This morning the Sun was more bright than usually is and many were gazing at the Sky !! – a very important Solar occurrence – passage of Venus across the Sun. Today, when looked at – [through protective welder’s glass] a black spot could be observed inside the Sun[around 0700 am at Marina beach] in say 10 O clock position – a small but observable one at that.  A grand spectacle as this is the last Venus transit this century; the prior transit took place on 8 June 2004. The previous pair of transits were in December 1874 and December 1882. After 2012, the next transits of Venus will be in December 2117 and December 2125.

It is the Sun which influences life on earth and other planets.  In their orbit of various planets, there would be movements when they cross the path of others.  Today, Venus passes directly between the Sun and Earth, becoming visible against (and hence obscuring a small portion of) the solar disk.  It is today, when  Venus can be seen from Earth as a small black disk moving across the face of the Sun. The duration of such transits is usually measured in hours (the transit of 2004 lasted six hours). A transit is similar to a solar eclipse by the Moon. While the diameter of Venus is more than 3 times that of the Moon, Venus appears smaller, and travels more slowly across the face of the Sun, because it is much farther away from Earth.

You get to know and read more about eclipses, especially the lunar and solar eclipse.  Factually, moon passes between Sun and earth every month, yet we do not see a solar eclipse every month. That’s because the moon’s orbit is also slightly inclined to earth’s orbit, so the new moon is usually a little above or a little below the sun.  The transit of Venus is essentially an annular eclipse of the sun by Venus.
the path of venus in 2004 and today - pic courtesy

Transits of Venus are among the rarest of predictable astronomical phenomena. They occur in a pattern that repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 years and 105.5 years.  If Venus and the earth orbited the sun in the same plane as the sun, transits would happen frequently.  However, the orbit of Venus is inclined to the orbit of earth, so when Venus passes between the sun and the earth every 1.6 years, Venus usually is a little bit above or a little bit below the sun, invisible in the sun’s glare.  Ascending-node transits occurred in December 1631, 1639, 1874, and 1882. The next ones occur in December 2117 and 2125. Descending-node transits occurred in June 1761, 1769, and 2004, with the next one coming June 5/6, 2012. After that, the next descending-node transits occur in June 2247 and 2255.

In 1716 astronomer Edmond Halley calculated that you can quantify the distance from the sun to the earth by having observers across the globe time the passage of Venus across the sun. For the 1761 transit and every transit opportunity since then, explorers sailed to distant lands to time the transit.  By quantifying the distance from the sun to the earth, a simple application of Kepler’s Third Law gives you the distances of all the planets from the sun, and thus the scale of the solar system.  Knowing the size of the solar system gives more accurate parallax measurements of distant stars.  Today, the transit of Venus as a means to measure the sun-earth distance is largely of historical interest, for tools such as radar have measured distances to planets much more accurately.

If one were to ask why does Venus take “only” 105½ years to go from a pair of June transits to a pair of December transits, whereas it takes 121½ years to go from a pair of December transits to a pair of June transits? – this  asymmetry is due to the fact that Earth's orbit around the Sun is not quite a perfect circle. It's slightly elongated (the technical term iseccentric), deviating from a perfect circle by about 3 percent. In contrast, Venus's orbit is so close to being a perfect circle that its minuscule elongation can be ignored in this discussion.
Scientifically, the starting phase of the event called 'Ingress Exterior' was visible in India, after sunrise for about 5 hours 30 minutes for the observers in the east of the country to about 4 hours 30 minutes for those in the west.  The entire transit event will be visible from north western North America, the western Pacific, northern Asia, Japan, Korea, eastern China, the Philippines, eastern Australia and New Zeeland.

So did you see Venus today – sure none of us would be alive to watch it again, when it occurs in Dec 2117.

With regards – S. Sampathkumar

1 comment:

  1. very explanative and elaborate - good source of education - Suraj