Averted vision

Interesting what Bert GrayMalkin says about things seen at the edge of our vision [ FT354:70]. In astronomy there is a technique called averted vision. Basically, this involves not looking directly at faint objects but around the edge. Our eyes have rod and cone cells, the rod (or I may be confused with the cones!) see in black and white and are much more sensitive to faint objects. However, they are found around the eyes’ edge, while the colour- seeing cones are in the centre. If you stare directly at say M51, a galaxy, with an underpowered instrument, in my case an 8x25 monocular, it’s hard to see it – but stare around the edge and it pops into view. Kevan Hubbard Oxford