The principle of parallax has never been more striking than it was yesterday, when duelling observations from space located one man – a rotund forty-nine-year-old Italian tourist who local guides have identified as Pablo Paunchetti, a shoemaker native of Turin – simultaneously at both ends of the Great Wall of China.
Parallax is the phenomenon by which a single object appears differently positioned when viewed along different lines of sight. The simple illustration below gives some sense of the effect.
The alert reader will note that in this illustration, the star-like object appears in front of the blue square from the perspective of viewpoint A, and in front of the red square from the perspective of viewpoint B. It is left to the imaginative reader to conjure the sort of scenario which would conclude with our star-like object appearing in front of the white square.
Using the angle of inclination between two lines of sight, astronomers have long been able to measure the distance to some of the closest stars in our universe. But yesterday it was the turn of astronauts to make the big discoveries.
As Tim Kopra of NASA and ESA’s Tim Peake loitered in low Earth orbit, gesturing warmly to one another from opposite sides of the International Space Station while in the process of carrying out non-essential external repairs, they took their habitual glances back down to Earth only to spot Paunchetti atop the Great Wall.
While Kopra spied the holidaying Italian in Dandong, the site of the Great Wall of China’s eastern extremity, Peake was meanwhile convinced that Paunchetti was instead in the vicinity of Jiayu Pass, at the Great Wall’s western terminus.
According to China’s State Administration of Cultural Heritage, the Great Wall is 21,196 km (13,171 miles) in length. Parallax was only able to occur over such a vast area because Paunchetti was in the process of jumping for a photograph at the time of the astronomers’ twin observations. Despite his bulk and the distraction of his quivering waistline, Kopra and Peake were in agreement when they stated that the Italian had jumped very high indeed.
Proper scientists and laymen alike have quarrelled over the Great Wall of China’s purported visibility from space, with some calling the idea no more than a myth. But thanks to NASA, ESA, and Pablo Paunchetti, the debate is now sure to rage for years to come.