The vertical north south plane still intersects the plane of the Greenwich meridian at some angle; that angle is the astronomical longitude, calculated from star observations.
2.
The seventh cathedral was constructed from 1870 to 1879 . It was solemnly blessed in December 1879 . The cross atop the central dome is a reference point of astronomical longitudes of the archipelago.
3.
The astronomical longitude of the Greenwich prime meridian was found to be 0.19 & Prime; ?0.47 & Prime; East, i . e . the plane defined by the local vertical on the Greenwich prime meridian and the plane passing through the Earth's rotation axis on the ITRF zero meridian are effectively parallel.
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