Man in the Moon in the context of Le Voyage dans la Lune

Bias is a disproportionate weight in favor of or against an idea or thing, usually in a way that is inaccurate, closed-minded, prejudicial, or unfair. Biases can be innate or learned. People may develop biases for or against an individual, a group, or a belief. In science and engineering, a bias is a systematic error. Statistical bias results from an unfair sampling of a population, or from an estimation process that does not give accurate results on average.

Pareidolia (/ˌpærɪˈdoʊliə, ˌpɛər-/; also US: /ˌpɛəraɪ-/) is the tendency for perception to impose a meaningful interpretation on a nebulous stimulus, usually visual, so that one detects an object, pattern, or meaning where there is none. Pareidolia is a specific but common type of apophenia (the tendency to perceive meaningful connections between unrelated things or ideas).

Common examples include perceived images of animals, faces, or objects in cloud formations; seeing faces in inanimate objects; or lunar pareidolia like the Man in the Moon or the Moon rabbit. The concept of pareidolia may extend to include hidden messages in recorded music played in reverse or at higher- or lower-than-normal speeds, and hearing voices (mainly indistinct) or music in random noise, such as that produced by air conditioners or by fans. Face pareidolia has also been demonstrated in rhesus macaques.

Máni (Old Norse: [ˈmɑːne]; "Moon") is the Moon personified in Germanic mythology. Máni, personified, is attested in the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturluson. Both sources state that he is the brother of the personified sun, Sól, and the son of Mundilfari, while the Prose Edda adds that he is followed by the children Hjúki and Bil through the heavens. As a proper noun, Máni appears throughout Old Norse literature. Scholars have proposed theories about Máni's potential connection to the Northern European notion of the Man in the Moon, and a potentially otherwise unattested story regarding Máni through skaldic kennings.

Lunar pareidolia refers to the pareidolic images seen by humans on the face of the Moon. The Moon's surface is a complex mixture of dark areas (the lunar maria, or "seas") and lighter areas (the highlands). Being a natural element seen constantly by humans throughout the ages, many cultures have seen shapes in these dark and light areas that have reminded them of people, animals, or objects, often related to their folklore and cultural symbols; the best-known are the Man in the Moon in Western folklore and the Moon Rabbit of Asia and the Americas. Other cultures perceive the silhouette of a woman, a crow, a frog, a moose, a buffalo, or a dragon (with its head and mouth to the right and body and wings to the left) in the full moon. To many cultures of Melanesia and Polynesia, the Moon is seen to be a cook over a three-stone fire. Alternatively, the vague shape of the overall dark and light regions of the Moon may resemble a Yin Yang symbol.

A moon face is a medical sign in which the face develops a rounded appearance (reminiscent of the "Man in the Moon") due to fat deposits on the sides of the face.