They concluded that the black drop results from blurring of the image (whether from Earth's atmosphere, or inevitable imperfections of the telescope) combined with the way that the disc of the sun fades in brightness towards its rim.

ECONOMIST: Transits of Venus

Dr Massey and his colleagues were able to map the matter (both dark and visible) in the bit of the firmament covered by the Cosmic Evolution Survey by looking for characteristic distortions in the shape of distant galaxies that only Hubble, which is beyond the image-blurring effects of the atmosphere, can see.

ECONOMIST: Cosmology: I spy with my little gravitational lens | The