Lunatic

Background
A lunatic (colloquially: "looney") is a commonly used term for a person who is mentally ill, dangerous, foolish or unpredictable, a condition once called lunacy.

The word lunatic is borrowed from Latin "lunaticus", which gains its stem from "luna" for moon, which denotes the traditional link made in folklore between madness and the phases of the moon. This probably refers to the symptoms of cyclic mood disorders such as bipolar disorder or cyclothymia, the symptoms of which may also go through phases. As yet there is little evidence for any causal link between phases of the moon and the progression of mood disorder symptoms.

In a 1999 Journal of Affective Disorders article, a hypothesis was suggested indicating that the phase of the moon may in the past have had an effect on bipolar patients by providing light during nights which would otherwise have been dark, and affecting susceptible patients through the well-known route of sleep deprivation. With the introduction of electric light, this effect would have gone away, as light would be available every night, explaining the negative results of modern studies. They suggest ways in which this hypothesis might be tested.

Mental institutions used to be called "lunatic asylums" or colloquially, "loony bins".

In Russian, Polish and Czech, a lunatic refers to a sleepwalker, literally "one who walks under the moon" or "moon walker".

In Romanian, a word with the meaning of "lunatic" is "zănatic", derived from Latin "dianaticus", from Diana, the Roman goddess of the Moon.

In England and Wales the Lunacy Acts 1890 - 1922 referred to lunatics, but the Mental Treatment Act 1930 changed the legal term to Person of Unsound Mind, an expression which was replaced under the Mental Health Act 1959 by mental illness. Person of unsound mind was the term used in 1950 in the English version of the European Convention on Human Rights as one of the types of person who could be deprived of liberty by a judicial process. The 1930 act also replaced Asylum by Mental Hospital. Criminal Lunatics became Broadmoor Patients in 1948 under the National Health Service Act. The terms are still used by journalists, especially in tabloid newspapers.

Lunar Distance
The term lunatic was also used by supporters of John Harrison and his marine chronometer method of determining longitude to refer to proponents of the Method of Lunar Distances, advanced by Astronomer Royal Nevil Maskelyne.

Later, members of the Lunar Society of Birmingham called themselves lunaticks. In an age with little street lighting, the society met on or about the night of the full moon.