Averted Vision

Messier 33 in the northern constellation of Triangulum

Compared to the Andromeda Galaxy, M33 or Triangulum Galaxy near the constellation Triangulum is very faint.  When observing any object of low surface brightness, deep-sky observers use a technique called averted vision, which involves concentrating on the target without looking directly at it.  Averted vision works because the eye’s visual receptors in the periphery of the retina (away from the center of the retina) are more sensitive to dim light.  In other words, there are more rods in the retinal periphery than there are in the center of the retina.