The mechanism behind seeing the entire Moon despite only a few photons reaching your eyes lies in the principles of human vision and the way our brains process visual information.
When light from the Sun reaches the Moon, it gets reflected in various directions. Some of these reflected photons happen to travel towards Earth, and a portion of them eventually reach your eyes. These photons carry information about the Moon's surface and its features.
Human vision relies on the eyes' ability to detect and process light. The photons that enter your eyes pass through the lens and reach the retina, which is a layer of specialized cells at the back of your eye. The retina contains photoreceptor cells called rods and cones, which are responsible for converting light into electrical signals.
The rods and cones in your retina are sensitive to different intensities and wavelengths of light. Cones are responsible for color vision and work best in bright light conditions, while rods are more sensitive to low light levels but do not differentiate colors.
The Moon appears bright in the night sky because the photons reaching your eyes are relatively few, but they are still enough to activate the rods and cones in your retina. These activated photoreceptor cells transmit electrical signals through the optic nerve to the visual processing centers in your brain.
Your brain receives these electrical signals and processes them to construct the image you perceive as the Moon. It combines information from different areas of your retina to create a coherent and detailed representation of the Moon's shape, texture, and features.
Despite the relatively small number of photons reaching your eyes, your brain is adept at interpreting the available information and filling in the gaps. It uses various cognitive processes, such as pattern recognition and spatial integration, to construct a complete image of the Moon based on the limited data received.
In summary, while only a few photons from the Moon reach your eyes, your visual system, including your retina and brain, works together to process and interpret this information, allowing you to perceive the entire Moon as a coherent and detailed object.