At night you only see faint stars if you look away.
Your retina carries about 120 million rods for dim light and some 6 million cones for colour and detail. In the fovea, your point of sharpest vision, there are essentially only cones – rods are absent there. That's why astronomers use averted vision and deliberately look slightly to the side.
Useful: A faint point of light vanishes the moment you fixate it, and returns off-centre.
Source: en.wikipedia.org