Neith (hypothetical moon)
Hypothetical moon of Venus, observed but never confirmed.
Neith is the name given to a supposed moon of Venus, first reported by Francesco Fontana in 1645. He described seeing small, moving dots near the planet, comparing them to fish in the sea. Giovanni Cassini spotted a small object near Venus in 1672, and again in 1686, when he formally announced a possible satellite. Over the next century, other astronomers—including James Short, Andreas Mayer, and Louis Lagrange—recorded around thirty sightings of the object, the last in 1770. However, no one saw it during the transits of Venus in 1761 and 1769, and many observers, such as William Herschel in 1768, failed to find anything. Cassini had estimated the object's diameter at one-quarter that of Venus. Lagrange calculated its orbital plane as perpendicular to the ecliptic in 1761, but mathematician Jean le Rond d'Alembert noted that year that the supposed moon did not appear during Venus's transit. In 1766, the director of the Vienna Observatory suggested the sightings were optical illusions caused by the bright image of Venus reflecting inside the telescope. J.H. Lambert later estimated its orbital period at eleven days and three hours. In 1884, Jean-Charles Houzeau proposed that the object was actually a planet orbiting the Sun every 283 days, coming into conjunction with Venus every 1080 days. Houzeau also gave it the name Neith, after an Egyptian goddess. A study by the Belgian Academy of Sciences in 1887 concluded that most sightings could be explained by stars near Venus, such as Chi Orionis, M Tauri, and Theta Librae. No space mission to Venus has ever found evidence of a natural satellite.
- First reported
- 1645 by Francesco Fontana
- Notable sighting
- 1672 by Giovanni Cassini
- Last reported sighting
- 1768 by Christian Horrebow
- Number of observations
- Up to 30
- Named by
- Jean-Charles Houzeau (1884)
- Status
- Hypothetical; no evidence found by space missions
Lore & Background
The first report of a moon of Venus was in 1645, by the Italian astronomer Francesco Fontana. He wrote that the dots were not always seen, but only when Venus was shimmering, and they moved back and forth like fish in the sea. In 1672, Giovanni Cassini found a small object close to Venus, but did not take great note until he saw it again in 1686, when he made a formal announcement. The object was seen by many other astronomers over a large period of time, including James Short in 1740, Andreas Mayer in 1759, Louis Lagrange in 1761, and Christian Horrebow in 1768.
Many astronomers failed to find any moon during their observations of Venus, including William Herschel in 1768. In 1761, Lagrange announced that Neith's orbital plane was perpendicular to the ecliptic. That same year, mathematician Jean le Rond d'Alembert wrote to Voltaire 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 were optical illusions, with the bright image of Venus reflected in the eye and back into the telescope, creating a smaller secondary image.
Reader's Guide
Neith represents a notable case in the history of astronomy of a spurious satellite—an object repeatedly observed but ultimately discredited. Its significance lies in how it illustrates the challenges of early telescopic observation, where optical artifacts, faint stars, and wishful thinking could produce persistent false detections. The Belgian Academy of Sciences published a paper in 1887 that studied each reported sighting and determined that most could be explained by stars such as Chi Orionis, M Tauri, 71 Orionis, Nu Geminorum, and Theta Librae. The saga of Neith also highlights the role of mathematical analysis, as J.H. Lambert estimated its orbital period as eleven days and three hours in 1777, and Jean-Charles Houzeau later suggested it was a planet orbiting the Sun every 283 days. Ultimately, no space mission sent to Venus has retrieved evidence of a natural satellite, confirming Neith as a phantom moon. Its legacy endures as a cautionary tale in observational astronomy and as a subject of historical study.
Did You Know?
- Neith was named after an Egyptian goddess by Jean-Charles Houzeau in 1884.
- The object was 'observed' up to 30 times by astronomers until 1770.
- In 1761, Louis Lagrange announced that Neith's orbital plane was perpendicular to the ecliptic.
- The Belgian Academy of Sciences in 1887 explained most sightings as stars near Venus, including Chi Orionis and Theta Librae.
More in Hypothetical astronomical objects 1-24
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record