Venus in transit... Science

# When Venus makes a transit

It was Jeremiah Horrocks who predicted that Venus transits occurred in pairs that were eight years apart - 375 years ago! Photo: K.R. Deepak   | Photo Credit: K_R_DEEPAK

I am going to take you 375 years back today. We’ll be tracking an event that took place on this day in 1639 (November 24 under the Julian calendar that was in use then in England, December 4 in Gregorian calendar).

No telephones or electricity. Even the notion that the Earth went around the Sun wasn’t completely accepted then. In such circumstances, it required someone like Jeremiah Horrocks, who would go on to be hailed as the Father of British astronomy, to predict and observe the transit of Venus.

A watchmaker’s son, Horrocks was born in Liverpool and won a place at Cambridge University while he was still a teen. He had read everything he could get his hands on and was therefore well versed in the works of Kepler and Copernicus. He confirmed Galileo Galilei’s discovery of Jupiter’s four large moons, found out about comets and is said to have in fact formulated his own theory of gravity, decades before Newton did. But the work that he became known for concerned Venus.

A hunch

Kepler, who established the laws of planetary motion, had correctly predicted the Venus transit of 1631 (for which there is no record of anyone witnessing it) and stated that the next one would occur only after 1756. Horrocks, however, believed that this calculation was wrong and got to work on his own.

Question
Can you tell me in which year Venus is expected to make its next transit? Send your answers to ganesh.a.s@thehindu.co.in with your name, class, school and location. [subject: eye]
Dual Tone Multi-Frequency works based on the table of frequencies shown (above). Therefore, if you were to dial ‘7’, the resulting sound would be composed of the two frequencies 852 Hz and 1209 Hz. Neeraj Kumar of class 10, S.V.M Residential Public School, Rajeev Nagar, Patna was the first to get it correct. Congratulations!
His results showed that Venus transits occurred in pairs that were eight years apart, then either 105 or 121 years later. What this meant was that the next one was due in 1639 and he also realised that this transit would be visible from Europe.

Horrocks wrote to his friend William Crabtree, urging him not to miss the spectacle. He set up his apparatus such that the telescope projected its view on a screen in a darkened room. You can imagine Horrocks’ joy when the black spot finally made its appearance on the card disc. Over the next few hours, he watched the transit, tracing his observations and timing each one. Crabtree, who was miles away but hampered by a cloudy sky, got his glimpse of the transit shortly before sunset.

What’s Venus Transit?

Venus transit occurs when Venus passes directly between the Sun and the Earth. Even though it is much bigger than our moon, it appears as a dot and doesn’t cause an eclipse like the moon as it is much farther away from our Earth.

A year and a few months after his historic prediction and observation, Horrocks died, aged just 22. By then, he had already used his data to show that the sun was in fact humongous and even confirmed that planets like Jupiter and Saturn were giants when compared to our Earth.

Observing Venus transits has enabled us to better understand Venus, its atmosphere and the solar system in general. The 2004-2012 pair has provided us with a wealth of information, especially with regard to studying exoplanets. This pair also implies that most of us wouldn’t be around when Venus next makes its transit.

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