Asked by: Leah Victoria Smith, Hereford
Astronomers call the technique ‘averted vision’, and it exploits the fact that our eyes contain two types of light-detecting cells. Around the centre of the retina are so-called cone cells, which give us colour vision and need good light levels.
Away from the centre are rod cells, which are responsible for black-and-white vision, and work better than the cone cells at low light levels. Looking off to one side allows more light from faint objects to strike the rod cells, and become visible to us.