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Neith is a hypotheticalnatural satellite ofVenus reportedly sighted byGiovanni 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.[1][2]
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.[3] The object was seen by many otherastronomers over a large period of time: byJames Short in 1740,[4] by Andreas Mayer in 1759,[4] by Louis Lagrange in 1761,[5] another eighteen observations in 1761, including one in which a small spot was seen following Venus while the planet was in atransit across theSun, eight observations in 1764, and byChristian Horrebow in 1768.[6]
| Year | City | Person | Number of sightings |
|---|---|---|---|
| 1645 | Naples | Francesco Fontana | 3[4] |
| 1646 | Naples | Francesco Fontana | 1[4] |
| 1672 | Paris | Giovanni Domenico Cassini | 1[4] |
| 1686 | Paris | Giovanni Domenico Cassini | 1[4] |
| 1740 | London | James Short | 1[4] |
| 1759 | Greifswald | Andreas Mayer | 1[4] |
| 1761 | Marseille | Joseph Lagrange | 3 |
| 1761 | Limoges | Jacques Montaingne | 4 |
| 1761 | St. Neots | unknown | 1 |
| 1761 | Greifswald | Friedrich Artzt | 1 |
| 1761 | Krefeld | Abraham Scheuten | 2 |
| 1761 | Copenhagen | Peter Roedkiær | 8 |
| 1764 | Copenhagen | Peter Roedkiær | 2 |
| 1764 | Copenhagen | Christian Horrebow and others | 3 |
| 1764 | Auxerre | Marian | 3 |
| 1768 | Copenhagen | Christian Horrebow | 1 |
Many astronomers failed to find any moon during their observations of Venus, includingWilliam Herschel in 1768[citation needed]. Cassini originally observed Neith to be one-fourth the diameter of Venus. In 1761, Lagrange announced that Neith'sorbital plane was perpendicular to theecliptic.[5] That same year, however, mathematicianJean le Rond d'Alembert wrote toVoltaire that Neith had "declined to follow his mistress during her passage over the sun", questioning whether Venus truly had a moon.[7] In 1766, the director of theVienna Observatory speculated that the observations of the moon wereoptical illusions. He said: "the bright image of Venus was reflected in theeye and back into thetelescope, creating a smaller secondary image."[citation needed] In 1777,J.H. Lambert estimated its orbital period as eleven days and three hours.[citation needed]
In 1884,Jean-Charles Houzeau, the former director of theRoyal 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 anEgyptian goddess.[citation needed]
TheBelgian 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, includingChi Orionis,M Tauri,71 Orionis,Nu Geminorum andTheta Librae.[citation needed]
To date, among thespace missions sent to Venus, none has retrieved evidence of a natural satellite of such planet.
