Final answer:
The most common standard can light fixture typically has a diameter of about 6 inches, widely used in various settings for recessed lighting.
Step-by-step explanation:
The diameter of the most common standard can light fixture can vary, but it's typically around 6 inches (or roughly 15.24 centimeters). This size is widely used in residential and commercial settings for recessed lighting. In terms of fixtures such as those used in astronomy, the subject matter does not directly address standard can light fixtures, instead discussing topics such as telescope diameters and the concept of stars as 'standard bulbs' in celestial navigation, light collecting area of a telescope, and the light gathering ability of the human eye's pupil under different lighting conditions.