Watching Mercury from Queensberry

Last week Wānaka-based astronomy enthusiast Martin Unwin observed the transit of Mercury across the sun at Queensberry—almost a quarter of a millennium since Captain James Cook saw the uncommon spectacle in New Zealand. 

The transit began around midnight on Monday November 11 and was visible via a protective telescope from sunrise on Tuesday November 12, from 6:00 am to 7.04 am.

Cook and his astronomer Charles Green watched the transit on November 10, 1769 at Mercury Bay on the Coromandel Peninsula. 

There are 13 transits of Mercury each century, and NASA said the next won’t occur until 2032. 

NASA said, “Viewers nearly everywhere on Earth will be able to see a tiny dark spot moving slowly across the disk of the Sun.”

The MetService reported inland in Southland and parts of Otago as having the best chance of clear skies in the country during the event.

“Watching the transit with your own eyes gives you a rare opportunity to see the solar system clockwork operating in real time, with Mercury's motion across the solar disc easily detectable over time scales as short as a few minutes,'' said Unwin. “Only the final stages of the transit were visible from New Zealand, for about 30 minutes after sunrise with the sun very low in the eastern sky. It was difficult to see from Wānaka, where the sun rises behind the Grandview Range, but we were able to get an excellent view from the terraces above Queensberry. From our vantage point at about 500 metres the sun cleared the eastern horizon behind Tarras just after 6:30 am, with Mercury finally crossing the edge of the sun at 7:04 am.”

Unwin added, “The real value of watching the transit is that it gives you a direct measure of the scale of the inner solar system. It is one thing to read that the sun is 140 million kilometres away, but another to actually see this for yourself. Through a telescope, masked with a solar filter, the sun is a grapefruit held at arms’ length. The black dot of Mercury in transit is as big as this full stop. The furthest our species has travelled, from the Earth to the moon, would take you barely a quarter of the way across the face of our nearest star.”


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