Looking slightly to the side of a faint object instead of straight at it. The centre of the retina has few rods, the cells that sense dim light; shifting your gaze by about ten degrees makes the object show up better. The gain is about one magnitude.
Related terms
- Dark adaptation
The time the eye takes to become sensitive in the dark: the pupil opens within seconds, but the retina gains most of its sensitivity over 20 to 30 minutes. A single bright white light undoes it all. That is why observers use a dim red light.
- Limiting magnitude
The brightness of the faintest stars you can see. With the naked eye it ranges from 3 or 4 in a city to 6.5 or more under a very dark sky. A telescope of aperture D (in mm) pushes it further by about 5 log₁₀(D ÷ 7) magnitudes: a 200 mm telescope reaches roughly magnitude 14.
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