Naked eye

In astronomy, the naked eye may be used to observe celestial events and objects visible without equipment, such as conjunctions, passing comets, meteor showers, and the brightest asteroids, including 4 Vesta.

Sky lore and various tests demonstrate an impressive variety of phenomena visible to the unaided eye.

Some basic properties of the human eye are: Visual perception allows a person to gain much information about their surroundings: The visibility of astronomical objects is strongly affected by light pollution.

Even a few hundred kilometers away from a metropolitan area where the sky can appear to be very dark, it is still the residual light pollution that sets the limit on the visibility of faint objects.

Under perfect dark sky conditions where all light pollution is absent, stars as faint as +8m might be visible.

In the center of a city, where the naked-eye limiting magnitude due to extreme amounts of light pollution can be as low as 2m, as few as 50 stars are visible.

Colors can be seen but this is limited by the fact that the eye uses rods instead of cones to view fainter stars.

Under typical dark sky conditions Uranus (magnitude +5.8) can be seen as well with averted vision, as can the asteroid Vesta at its brighter oppositions.

Close to sunset and sunrise, bright stars like Sirius or even Canopus can be spotted with the naked eye as long as one knows the exact position in which to look.

Some 100 satellites per night, the International Space Station and the Milky Way are other popular objects visible to the naked eye.

Comparing the zenith with the horizon shows how the "blue quality" is degraded depending on the amount of air pollution and dust.