Mercury makes a rare move across the Sun

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.

In a rare astronomical phenomenon that occurs only 13 times in a century, planet Mercury was seen as a dot on the solar disc from several parts of India today.

The transit of Mercury was visible from most parts of of Asia, Europe, Africa, Greenland, South America, North America, Arctic, North Atlantic Ocean and much of the Pacific Ocean area.

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To catch a glimpse, viewers need binoculars or telescopes with protective solar filters. Mercury’s journey can also be seen via a livestream on NASA’s website.

In New Delhi, the transit began at 4.43 p.m. and lasted till 6.48 p.m. >More..

Children watching the transit >t hrough a telescope at Anna Science Centre - Planetarium in Tiruchi on Monday. Photo. M. Moorthy

Historical significance

Until the end of the 17th century, there was no mechanism for calculating the distance from the Sun to the Earth. The relative distances between planets were known, for example, that Jupiter is about five times as far from the Sun as the Earth is. To calculate this, at least one absolute distance was needed, namely, the Earth-Sun distance.

Sir Edmund Halley observed a mercury transit in 1677 and realised that if the time taken for the planet to transit were measured from two different spots on Earth, this could be used to measure the Earth-Sun distance, which could be used to calculate the distances of other planets, absolutely.

>All you need to about the phenomenon