AGARTALA, May 9 (TIWN): Along with the nation Tripura on Monday witnessed astronomical phenomena when exactly at 4.40 p.m. mercury came exactly in between the Sun and the Earth, and a small dark spot was witnessed moving across the face of the Sun.Tripura witnessed this view from Sukanta Academy from Monday.The phenomenon was witnessed across the country until the local time of sunset and will last nearly five hours and it was an astronomical phenomenon that took place approximately 13 times in a century.Since Mercury is tiny, a telescope was required to observe the transit. People were advised not to look at the Sun directly or through any optics, as they may risk permanent blindness. The safest way to view it is by projecting the image of the Sun onto a sheet of paper and looking at that image. Seeing the Sun and the transit of Mercury by projecting its image on a sheet is perfectly safe.On an average, about 13 transits of Mercury take place in a century. The 20th century saw 14 transits and the 21st century too will see 14 transits.

However, the 22nd century will see 13 transits.

 These are global numbers, with a single location on the Earth not necessarily having visible access to all the events.In contrast, transits of Venus are very rare. 

There were two events in this century — in June 2004 and June 2012. The next transit of Venus will take place in 2117 and 2125.Transits of Mercury are, however, not as rare as those of Venus, but not very frequent either. In recent times, the transits of Mercury took place in 2003 and 2006.The next transit on view from India will be in 2032.