The Wikipedia article for Venus's alleged moon Neith has this picture:

enter image description here

And a tantalizing remark regarding paramecia (vandalism?). I know the grey ball is supposed to be Neith, the white is Venus, the little rods are the halo of light. But why is Venus shaped like a kidney? Is this supposed to be a partially lit Venus? Then why is Neith never behind it?

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    $\begingroup$ According to to Wikipedia the images are woodcuts by Francesco Fontana (1580–c. 1656) an Italian lawyer (University of Naples) and an astronomer.(en.wikipedia.org/wiki/Francesco_Fontana) Perhaps more a history of science topic. $\endgroup$ – M. Enns Jul 25 '16 at 19:18
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    $\begingroup$ That's probably what they think they saw in the best (or not even) telescopes they had back then. The theory of optical imaging errors was not developed until the mid to late 19th century, so it's not surprising that older observers would trust their instruments and eyes a little too much. $\endgroup$ – CuriousOne Jul 25 '16 at 19:24
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    $\begingroup$ Strictly speaking, the answer to your question is that what is depicted in these pictures is nothing on Earth. $\endgroup$ – tparker Jul 25 '16 at 23:51
  • $\begingroup$ @tparker But it's depicting the image of Venus generated at the telescope eyepiece on Earth... And it's also a picture of a book that was written on Earth... =] $\endgroup$ – Superbest Jul 26 '16 at 3:08
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    $\begingroup$ "why is Neith never behind it?" -- I'm going to say because this is a selected series of drawings of Venus together with (what Fontana believed to be) Neith. Any pictures Fontana drew of Venus in which he didn't see Neith, and concluded that it was behind Venus, would not have been selected to illustrate Neith. Similarly, any pictures he drew of his cat have not been selected for inclusion in this series, it doesn't follow that he never saw a cat ;-p $\endgroup$ – Steve Jessop Jul 26 '16 at 10:08

According to the caption for that picture on the same Wikipedia article, it is

Francesco Fontana’s drawing of the supposed satellite(s) of Venus. Woodcuts from Fontana’s work (1646). The fringes of light around Venus are produced by optical effects.$^1$

Fontana lived from around 1580 to around 1656. He was an Italian lawyer at the University of Naples and an astronomer, using a hand-made telescope. He observed the Moon and the planets of the solar system, recording observations and drawing them. Most of these were published in his book Novae coelestium terrestriumq[ue] rerum observationes, et fortasse hactenus non vulgatae in 1646. 1645 was when he made his observation of a Venusian moon.

It is interesting to note that according to the book cited by Wikipedia (The Moon that Was not: The Saga of Venus' Spurious Satellite by Helge Kragh), Fontana's contemporaries thought he was a good telescope maker (his were some of the best of the day) but a poor astronomer. Contemporaries said his observations were ridiculous and fantasies. One even wrote about his published book of observations, "I have the book of foolishnesses observed, or rather dreamed, by Fontana in the heavens. If you want to see insane things...I will send you the book." He was scorned by Galileo and one of Galileo's protégés as well. It also appears that he didn't think the obviously optical effects in his woodcut were optical.

Fortana was the first to observe a "moon" of Venus, according to Wikipedia. This he also published in his book of observations, and he was thought ridiculous for this (at least until other, more reputable astronomers sighted something similar). The mention of paramecium is just there saying the depiction of Venus and later depictions of paramecium are similar. Interestingly, Fontana shows two moons in one panel. I found no references to a second theoretical Venusian moon anywhere, but maybe Neith is sometimes in front and sometimes behind, but moon number two is making things confusing.

As for why Venus is kidney shaped, that's probably the least confusing part. Venus often appears as a not-complete circle, as it has phases like the moon, as shown below:

venus phases

Hope this helps!

Kragh's book can be found here; the relevant part is chapter two, section 2.1.

$^1$See this website

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Generally speaking, Venus is rarely a full disk, because it's inwards from the Earth's orbit, so it displays a full cycle of phases. Mostly, it looks like this:

Image source

Thus, it's not surprising that Fontana would depict it like that, since most of the time Venus appears partially full or as a crescent. Moreover, the only times when Venus appears almost full is when it is diametrically opposite from Earth in its orbit, so it is small, faint, low in the sky, and close to the Sun, so it is harder and harder to observe the 'fuller' it is.

I tried to get a bit more detail, and the woodcuts appear in p. 10 of H Kragh's The Moon that Wasn't: The Saga of Venus' Spurious Satellite (google books link), but I can't quite get a correspondence that makes sense.

As to why Neith is never behind it, you'd have to ask Fontana. (While you're at it, ask him to double-check his observations.) However, I don't find the reported range of Neith positions particularly suspicious or surprising - it's shown at pretty representative ranges of where you'd expect it, particularly given the quality of Fontana's representations. The only part of the orbit this misses are wider approaches and occultations, and the latter are very rare since planets' shadows are generally small compared to their satellites' orbits.

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  • $\begingroup$ Seeing the same moon twice is a little suspicious of an optical defect in the instrument, isn't it? :-) The only problem I have with that hypothesis is that optical reflections would have moved when the instrument was moved, so they should have been obvious to the observer. $\endgroup$ – CuriousOne Jul 25 '16 at 20:08
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    $\begingroup$ @CuriousOne Francisco Fontana may not have been a great scientist, but he was passionate about observations and he observed the planets and moon extensively through his telescope, even writing a book on his observations, with what to us look like bad drawings, but which at the time were cutting edge observations. The false image of a moon around Venus is thought to be caused by light reflecting off the eye back into the Telescope. Several people fell for that false image including Cassini. It wasn't till over 100 years later that Venus' moon was dismissed. $\endgroup$ – userLTK Jul 25 '16 at 20:12
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    $\begingroup$ @userLTK: If one can show that the reflection remains largely independent of the orientation of the instrument (and the eye?), that would convince me that what he saw was an optical error. Thanks for the links! $\endgroup$ – CuriousOne Jul 25 '16 at 20:25
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    $\begingroup$ @CuriousOne That's a really interesting question. You can certainly get flare like that from poorly made optics. However, Fontana was respected as a telescope maker, even by Galileo, and Galileo found his five moons of Jupiter, so I think the technology, in this specialist application, was good enough then to avoid all cheap optics artifacts, otherwise Galileo wouldn't have found what he did. I think the most likely explanation was that Fontana was 65 years old at the time of the observation, so his own optics / sight was probably beset by "floaters" and other effects that can beget flaring. $\endgroup$ – Selene Routley Jul 26 '16 at 0:03
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    $\begingroup$ "Moreover, the only times when Venus appears almost full is when it is diametrically opposite from Earth in its orbit, so it is small, faint, low in the sky, and close to the Sun, so it is harder and harder to observe the 'fuller' it is." This occurred to me whilst reading the other answers. Frankly I'm surprised it can be seen at all in this position! $\endgroup$ – Lightness Races in Orbit Jul 26 '16 at 9:15

Galileo was the first to observed the phases of Venus, also here, which he was able to do by his telescope, around 1610. It was the phases of Venus as well as observing Jupiter's moons orbiting Jupiter, that, to Galileo, confirmed without any question that Copernicus' model was the correct one and planets orbited the sun and moons orbited planets. Galileo's publications of 1613 were banned in 1616 and in 1633 he was put on trial and sentenced to house arrest, narrowly escaping the death penalty. Timeline here.

Francesco Fontana and here, was inspired by Galileo and while he was also an artist and a lawyer, he also constructed his own telescope and extensively observed the moon and planets and he made similar wood carvings of all the known planets and detailed observations of the moon. A crater on the moon is named after him.

That particular drawing, or printing is probably more correct, as it was made from woodcuts, was done in 1646, about 4 years after Galileo's death. It seems to show the phases of Venus as well as a moon or a few moons orbiting Venus. As strange as that picture looks today, it was pretty cutting edge astronomy at the time, and it was (perhaps) still dangerous to make that claim in 1646. I'm not sure of that, but that printing might have been scandalous at the time.

Fontana claimed to have observed a moon around Venus in 1645. Cassini and several others also made that observation, See here. Cassini in 1672, and by that same article, the first recorded observation in 1650, which is a little inconsistent, but in the same time period. It's entirely possible that Fontana observed what he thought was a moon or moons around Venus by telescope.

Neith is a hypothetical natural satellite of Venus reportedly sighted by Giovanni Cassini in 1672 and by several other astronomers in following years. The first supposed sighting of this moon was in 1650. 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 1769.8

and a likely explanation for the moon from that same source.

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 and back into the telescope, creating a smaller secondary image."

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  • $\begingroup$ The Galileo trial went a little bit differently as it is well-known, I suggest to read after independent historical viewpoints, too. Most of the story is an anti-Church invention from the XVIII-XIX century. For example, he never said, that "the Earth still moves". $\endgroup$ – peterh - Reinstate Monica Jul 25 '16 at 22:33
  • $\begingroup$ @peterh I'm not an expert on the trial, though I've read a little. He wasn't convicted and sentenced to house arrest till 1633, so the trial came much later. His writings were objected to as early as 1613 and banned in 1616. He spent some time trying to get them unbanned between 1616 and 1633. I should probably clean up that part of my answer, but it doesn't really affect the specific question. Fontana did like and respect Galileo and probably shared his viewpoint on Venus orbiting the sun. The crescent Venus is probably paying homage to Galileo I would think. $\endgroup$ – userLTK Jul 25 '16 at 23:34
  • $\begingroup$ Bellarmine's view wasn't the geocentric world-view, his view was that Galileo doesn't have enough evidence for a clear decision. And yes, he really didn't have enough (at the time - Herschel didn't exist yet). His theory based on the at the time available evidence weren't acceptable even today. The "house arrest" meaned that he has lived from the money of the Pope in his own house, where he could still write books and publish them. The real reason behind the trial was that he wasn't really polite in his books with the (sometimes powerful) people having different opinions as his own. $\endgroup$ – peterh - Reinstate Monica Jul 26 '16 at 0:17

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