Neith is a hypothetical

natural satellite A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are colloquially referred to as moons, a deriv ...

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

reportedly sighted by Giovanni Cassini in 1672 and by several other astronomers in following years. It was 'observed' up to 30 times by astronomers until 1770, when there were no new sightings and it was not found during the transit of Venus in 1761 and 1769.

Discovery

In 1672, Giovanni Cassini found a small object close to Venus. He did not take great note of his observation, but when he saw it again in 1686, he made a formal announcement of a possible moon of Venus. The object was seen by many other

astronomers An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, moons, comets and galaxies – in either observ ...

over a large period of time: by James Short in 1740, by Andreas Mayer in 1759, by Louis Lagrange in 1761, another eighteen observations in 1761, including one in which a small spot was seen following Venus while the planet was in a

transit Transit may refer to: Arts and entertainment Film * ''Transit'' (1980 film), a 1980 Israeli film * ''Transit'' (1986 film), a Canadian short film * ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countrie ...

across the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

, eight observations in 1764, and by Christian Horrebow in 1768.

Summary of sightings

Observations

Many astronomers failed to find any moon during their observations of Venus, including

William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...

in 1768. Cassini originally observed Neith to be one-fourth the diameter of Venus. In 1761, Lagrange announced that Neith's

orbital plane The orbital plane of a revolving body is the geometric plane in which its orbit lies. Three non-collinear points in space suffice to determine an orbital plane. A common example would be the positions of the centers of a massive body (host) a ...

was perpendicular to the

ecliptic The ecliptic or ecliptic plane is the orbital plane of Earth's orbit, Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. Fr ...

. That same year, however, mathematician

Jean le Rond d'Alembert Jean-Baptiste le Rond d'Alembert ( ; ; 16 November 1717 – 29 October 1783) was a French mathematician, mechanician, physicist, philosopher, and music theorist. Until 1759 he was, together with Denis Diderot, a co-editor of the ''Encyclopé ...

wrote to

Voltaire François-Marie Arouet (; 21 November 169430 May 1778), known by his ''Pen name, nom de plume'' Voltaire (, ; ), was a French Age of Enlightenment, Enlightenment writer, philosopher (''philosophe''), satirist, and historian. Famous for his wit ...

that Neith had "declined to follow his mistress during her passage over the sun", questioning whether Venus truly had a moon. In 1766, the director of the Vienna Observatory speculated that the observations of the moon were optical illusions. He said: "the bright image of Venus was reflected in the

eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

and back into the

telescope A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...

, creating a smaller secondary image." In 1777, J.H. Lambert estimated its orbital period as eleven days and three hours. In 1884,

Jean-Charles Houzeau Jean-Charles Houzeau de Lehaie (October 7, 1820 – July 12, 1888) was a Belgian astronomer and journalist. A French speaker, he moved to New Orleans after getting in trouble for his politics in Belgium. In the U.S. he continued his journalisti ...

, the former director of the Royal Observatory of Brussels suggested that the "moon" was actually a planet which orbited the Sun every 283 days. Such a planet would be in conjunction with Venus every 1080 days, which fit with the recorded observations. Houzeau was also the first to give the object the name Neith, after an Egyptian goddess. The Belgian Academy of Sciences published a paper in 1887 which studied each reported sighting of Neith. Ultimately, they determined that most of the sightings could be explained by stars which had been in the vicinity of Venus, including Chi Orionis, M Tauri, 71 Orionis, Nu Geminorum and Theta Librae. To date, among the space missions sent to Venus, none has retrieved evidence of a natural satellite of such planet.

References

Sources

* *

External links