Don't tell the swarms of tourists paying nearly $15 to pose with one leg on either side of the prime meridian at the Royal Observatory in Greenwich, England, but Earth's true prime meridian actually passes through a park approximately 334 feet to the east near a trash can. And admission is free. Phys.org reports the prime meridian—"the north-south line marking zero degrees longitude" that serves as the starting point from which time zones are measured—is not quite where international representatives placed it in 1884. That's the conclusion of GPS-armed researchers, who published their conclusions in the Journal of Geodesy. To arrive at the now-incorrect meridian, scientists used a bowl of liquid mercury to position a telescope exactly vertical to the "clock stars" above.
The Independent explains that the telescope determined local time "by marking the exact moment a clock star" passed—and achieving exactness meant the telescope had to be "absolutely perpendicular to the Earth." But the earth is not uniformly round, and gravitational effects vary. A subtle gravitational "deflection" affected things in Greenwich, reports Phys.org, something the researchers determined by way of GPS, which is essentially able to take measurements unaffected by gravity and terrain. The conclusion won't have a ripple effect: The researchers analyzed other coordinates across the globe to verify the effect is specific to Greenwich. Further, "the orientation of the meridian plane used to measure Universal Time has remained essentially unchanged," they write.