May 25, 2022
In astronomy, the naked eye is an expression that indicates observations conducted without the aid of any instrument, such as telescopes or binoculars, but only the human eye. It is used to refer to celestial bodies and phenomena visible to anyone, such as the planets closest to the Earth, stars of lower apparent magnitude, astronomical conjunctions, some comets, some meteor showers. Normally the naked eye can see stars with an apparent magnitude of less than 6 and the angular resolution is about 3 arc minutes. For example, it is possible to separate the main components of the quadruple star ε Lyrae with the naked eye and observe the planet Uranus. This performance requires optimal conditions, such as excellent sky transparency and a dark, light pollution-free environment. Some people have more acute eyesight: unverifiable anecdotes, report the naked eye vision of the Galilean satellites of Jupiter or the phases of Venus. The farthest object visible to the naked eye is the Triangle Galaxy.