Astronomers today are preparing for one of the highlights of the skywatchers' year, when the Sun, Mercury and Earth all line up, a phenomenon that happens just a dozen or so times per century. <br/><br/>Mercury will be seen through telescopes as a black dot inching over the face of our star, providing a celestial spectacle, weather permitting, that will last seven and a half hours. The smallest recognised planet in the Solar System, Mercury completes an orbit every 88 days, and passes between the Earth and the Sun every 116 days.<br/><br/>According to Britain's Royal Astronomical Society, most of Western Europe, the western parts of North and West Africa, eastern North America, and most of South America will be able to view the entire transit.<br/><br/>The rest of north and south America, the eastern Pacific, the remainder of Africa and most of Asia, will see parts of the event.<br/>Observers in east and southeast Asia and Australasia, however, will miss out entirely.

In a rare astronomical phenomenon that occurs only 13 times in a century, planet Mercury will be seen as dot on the solar disc from various places of India today.<br/><br/>This phenomenon takes place when the planet will be seen as a small black dot travelling from one limb of the solar disc to the other.<br/><br/>This occurs only when the Sun, Mercury and the Earth lined up in one plane. It appears as a dot on the disc because its angular size is very small compared to that of the Sun as seen from the Earth.<br/><br/>The phenomenon is a relatively rare one which occurs 13 or 14 times in a century. It occurs in May and November, a statement by the Ministry of Earth Sciences said.<br/><br/>In Delhi and Mumbai the event can be seen for a duration of about 2 hours 20 minutes as it will start at 4:41 P.M.<br/><br/>Similarly, in Kolkata and Chennai the event will start at 4:41 P.M. and it can be seen for a duration of about 1 hour 26 minutes, the statement said.<br/><br/>The next transit of Mercury will take place on November 11, 2019, however it cannot be seen from India as the same will begin after the sunset time of the places in the country.