Planet Mercury is making a rare transit where the smallest planet passes across the face of the earth.
During the transit, Mercury would appear as a dark silhouetted disc against the bright surface of the sun.
There are 14 transits this century; the last was in 2016, but the next one will not be until 2032.
The transit began at 12:35 GMT, when the edge of Mercury appeared to touch the edge of the sun.
It will end at 18:04 GMT, when the edge of the silhouetted planet appears to leave the sun's disc.
The public has been advised by astronomers to be careful, as looking at the sun without protection can seriously damage the eyes.