Johann Schröter and Carl Harding observed the Ashen Light in early 1806. Their accounts were simultaneously reported in this journal. Schröter only made one observation on February 14 despite numerous attempts thereafter. Harding made three observations on January 24, February 28, and March 1. It's worth noting that Schröter failed to observe the Ashen Light on February 28 even though Harding was successful. Both of them initially dismissed the phenomenon as an optical illusion before accepting its objective reality. Harding even invited a lens-maker named Johann Gotthard to corroborate the sighting. The Ashen Light does not appear to have been described as "ashen" prior to these two observations. Schröter described the color as "aschgraue" (ash-grey) while Harding used the terms "aschgräuliches" (ash-greyish) and "rothgräulichem" (red-greyish). Schröter later finalized his thoughts on the matter in reference #1a below. Pages 164-167 cover Schröter's account. Pages 167-171 cover Harding's account.

The terms "earthshine" and "earthlight" are sometimes used interchangeably but they do have slightly different meanings. Earthlight is sunlight reflected by the Earth. Earthshine is specifically when earthlight illuminates the nightside of the Moon.

In the 17th and 18th century, there were many reported observations of a Venusian moon. But when Venus transited the Sun on June 6, 1761, all but three observers (Abraham Scheuten, Friedrich Artzt, and an unnamed British astronomer) failed to detect this phantom satellite. This convinced the broader scientific community that the satellite of Venus was an illusion. But sporadic sightings of Venusian satellites and intramercurial planets continued well into the 19th century.

An examination of alleged observations of Venusian satellites or intramercurial planets by Belgian astronomer Paul Stroobant. Stroobant ultimately ascribe these observations to misidentified stars, sunspots, or optical illusions.

German-born British astronomer William Herschel (famous for discovering the planet Uranus) thought of the Sun as an enormous planet. The Sun was therefore enveloped by a "luminous atmosphere" and sunspots provided a "transient glimpse" of the true surface underneath. An idea first proposed by Alexander Wilson in reference #53. Herschel argued that this solar interior appeared dark because it was much cooler than the blazing exterior. As such, Herschel saw no reason for why the interior of the Sun could not be inhabited. He later expanded upon these ideas in reference #51.

German astronomer Franz von Gruithuisen likened Venus to Earth. The climate was temperate and the surface was covered by many inland seas and luxuriant forests. He believed that Venus was inhabited by an intelligent species akin to humans. These Venusians were less advanced than us but their society, culture, and overall way of life reflected our own. Gruithuisen cautiously ascribed the Ashen Light to celebratory conflagrations lit by the Venusians.

By the early 19th century, the diameter of Venus had been measured to within a few percent of its modern value. I've included two examples below. One from before the turn of the century and one from after.

Following a long series of observations, Johann Schröter concluded that the atmosphere of Venus was comparable to the atmosphere of Earth. While he correctly surmised that the atmosphere was opaque, he was led astray by illusory sightings of enormous mountains.

After a few months of study, American astronomer Percival Lowell concluded that Venus was a "very drab-like thing" with a "bare desert-like surface". Lowell also drew parallels between the lineae on Venus to those observed on Mars. However, he thought they had a "purely natural" appearance, unlike the "artificiality observable in the lines of Mars". He ascribed the markings to geological formations on the surface.

German astrophysicist Johann Zöllner compared Venus to primordial Earth and suggested that a "not-too-deep sea" covered the entire planet.

Swedish Nobel Prize winning chemist and physicist Svante Arrhenius believed that "everything on Venus is dripping wet" (lol) and that the average temperature hovered around 47 °C. Arrhenius did not believe that Venus was home to an intelligent species but supposed that "low forms of life" and "luxuriant vegetation" adorned the surface. First published in Swedish in 1915 as "Stjärnornas Öden".

This illustration of a cityscape on Venus was drawn by famous cartoonist and animations pioneer Winsor McCay. It was largely based on the information provided by reference #15. I was unable to fit this into the video but you may notice that the cityscape is confined to the terminator. That's because, in reference #23, Giovanni Schiaparelli had falsely concluded that Venus was locked in synchronous rotation with the Sun. This meant that one side of the planet was always facing the Sun, much like how one side of the Moon is always facing the Earth. One hemisphere scorched by everlasting sunlight. The other, frozen in perpetual darkness. As such, any Venusians had to be confined to the terminator. The eternal twilight-zone between day and night.

The illustration of reference #14 was largely based on this pamphlet by Charles Housden which, in turn, was largely based on the observations made by Percival Lowell.

I suspect that some viewers will be a bit confused by my use of the word "asunder". These days, the adverb "asunder" is almost exclusively used in the sense of "into separate parts". However, it can also be defined as "apart from". Some archaic definitions even include "different" or "distinct in nature" which perfectly complements the topic of the video. So a less poetic reading of "bygone visions of life asunder" would be something like "past visions of life apart/distinct (from us)". Allowing for a more interpretive reading, one could even incorporate the modern definition of the word. Something like "past visions of extraterrestrial life torn asunder by newfound understanding". But, more than anything, it sounded kinda neat. I thought about using "life asunder" in the title but due to its ambiguity, I went with "cosmic neighbors" instead.

Czech chemist and astronomer Vojtěch Šafařík held a lecture in Prague in 1873 during which he listed 22 observations of the Ashen Light. Šafařík was evidently unaware of the observation made by Giovanni Riccioli in 1643. See reference #45. Šafařík considers a handful of hypotheses before ascribing the Ashen Light to a vast phosphorescent ocean which he believes covers the whole surface of Venus. His name has been incorrectly recorded as "A. Šafařík" due to a common mix-up between the names Vojtěch and Adalbert. See reference #18b.

In 1883, Czech physicist and meteorologist Václav Zenger rediscovered Giovanni Riccioli's largely forgotten 1643 observation of the Ashen Light. See reference #45. Zenger likened the Ashen Light to earthshine and believed the two phenomena shared a common cause.

The Ashen Light was briefly reviewed by Irish astronomer and author Agnes Clerke in this popular science book from 1885. To my knowledge, this is the first use of the term "Ashen Light" in English. Agnes Clerk should not be confused with her older sister, Ellen Clerke, who published a book about Venus in 1893 in which the Ashen Light is also mentioned.

Percival Lowell dedicated the last two decades of his life to planetary astronomy and spent much of that time observing Venus. While he acknowledged the existence of the Ashen Light on page 535 of this article, there is no evidence that he ever observed the phenomenon himself. See reference #22 for more examples of astronomers who failed to observe the Ashen Light.

Author John Barentine has written the definitive book on the Ashen Light. The book chronicles the history of this enigmatic phenomenon and the many attempts to solve it. Barentine ultimately concludes that the green-line airglow/aurorae of reference #118 is the most probable explanation. He does acknowledge that it could be a subjective illusion but also notes that "were the Ashen Light nothing but wishful thinking, it would have disappeared long ago with debunked astronomical ideas like the 'canals' of Mars and the undiscovered planet Vulcan."

In this three-part "historical review", Schiaparelli attempted to ascertain the rotation period of Venus. He reviewed observations made by Giovanni Cassini, Jacques Cassini, Francesco Bianchini, Johann Schröter, Francesco de Vico, and a few others. All of whom argued for a rotation period of approximately 24 hours. After conducting a 3-month-long survey of Venus, Schiaparelli concluded that it was locked in synchronous rotation. He arrived at this conclusion by tracking the movement (or, rather, lack thereof) of various spots and streaks. Schiaparelli ascribed these markings to atmospheric phenomena. In the end, both Schiaparelli and his predecessors were led astray. Venus takes 243.69 days to complete a rotation around its axis.

This is a synthesis of observations of Venus compiled by French astronomer André-Louis Danjon. By examining drawings of Venus produced by both himself and his contemporaries, Danjon reaffirmed Schiaparelli's conclusion that Venus was locked in synchronous rotation. Danjon also observed the Ashen Light which he dismissed as an illusion. See reference #48 for a more detailed breakdown of Danjon's objections to the Ashen Light.

Italian astronomer Giovanni Schiaparelli was the first to observe somewhat linear markings on Mercury. The near lack of movement of these markings led Schiaparelli to falsely conclude that Mercury was locked in synchronous rotation. The year before, Schiaparelli had made a similar proclamation in reference #23 about the rotation of Venus.

Balkan astronomer Leo Brenner (pen name of Spiridon Gopčević) could only discern amorphous streaks on Mercury.

American astronomer Percival Lowell could discern clearly defined lines on the surface of Mercury.

The two French astronomers Georges and Valentin Fournier recorded both curved and straight lines on Mercury.

French astronomer and popular science author Camille Flammarion compiled and reviewed a great number Martian Canal observations in this influential book.

In these three complementary books, American astronomer Percival Lowell outlined his beliefs that Mars was inhabited by intelligent beings. The Martian Canals are meticulously analyzed and illustrated. Lowell ultimately ascribed the canals to a vast irrigation network. A belief which he maintained until his death in 1916.

British scientist Alfred Russel Wallace was extremely skeptical of the Martian Canals and especially of Percival Lowell's interpretations. So much so that he dedicated an entire book to refute Lowell's theories.

The second- and fourth chapter of this book provides a good overview of the Martian Canals. The section titled "Antoniadi and the Attack on the Canal Theory" is about Eugène Antoniadi and his skepticism of Percival Lowell's theories about Mars. Antoniadi was initially a proponent of the Martian Canals and even drew networks of straight lines on some of his early maps. He eventually changed his mind, however, and came to believe they were illusory.

The War of the Worlds was first published in a serialized format between April and December of 1897. It was then published as a novel in 1898.

Madame Anne Emilie Clara Guzman (neé Goguet) was the window of a wealthy French industrialist named Marc Guzman. She died at her home in Pau, France, on June 30, 1891, at the age of 87. She left behind a will which stipulated that 100 000 francs were to be awarded to "the person who finds the means of communicating with a heavenly body". While Mme. Guzman used the French word "astre" which literally means "star", the intended meaning was clearly "heavenly body" or even "planet" as evident by her exclusion of the planet Mars. Mars was excluded because Mme. Guzman thought it was already "sufficiently well known". She dedicated this prize to her late son, Pierre Guzman, who likely died of heart disease on May 7, 1886, at the age of 52. Author Frank Winter writes that the 100 000 francs would have been worth "about $20,000" in 1891 which is consistent with other sources. Using that figure as a base and adjusting for inflation, the prize money would have been worth approximately $600 000 in 2022.

As indicated by the front matter of the book, it was "written under the sponsorship of the national aeronautics and space administration". I was unable to determine the exact date of publication but, based on dates and events mentioned in the book itself, it was published between the end of March and early July.

The two maps of Mars featured near the end of this blog article were published by geography divisions of the US Army and Air Force. The first map is simply labeled "Pictorial Representation of Mars" and was compiled from "astronomers' notes, observatory observations, and from various sources". The second map is labeled "MEC-1 Prototype" and was prepared by Earl C. Slipher at the Lowell Observatory. Slipher was, perhaps, one of the last proponents of the Martian canals. These maps were later used by NASA scientists during the Mariner 4 mission. In fact, a cropped sections of the second map is actually featured in reference #39 on page 266 and elsewhere.

The results of this experiment by Joseph Evans and Walter Maunder questioned the objective reality of the Martian Canals. The participants were all male students between the ages of 12-14 (some were "a little older or a little younger") and were seated between 15-62 feet (4.6-18.9 meters) from the illustrations. The illustrations used in the experiment were all based on genuine sketches of Mars, except the linear markings had either been erased or replaced with tiny dots and/or squiggly lines. None of the students had any prior knowledge of the Martian Canals and were simply instructed to reproduce each drawing "as well as they could". Proponents of the canals questioned the methodology of the experiment and the objectivity of the experimenters. These concerns were not entirely unfounded as evident by reference #32 and reference #40a below. But even if the experiment was flawed, a seed of doubt had nonetheless been planted. A seed which continued to grow until the Martian Canals had been reduced to myth.

Beginning in 1901, Percival Lowell made repeated attempts to acquire photographic evidence of the Martian Canals. Numerous photographs were printed in various publications. Lowell thought some of the photographs proved "the existence of the canals" and that they were "continuous lines and not a synthesis of other markings" as some of his critics had supposed. See reference #40. But the photographic plates were tiny and of low resolution. It was difficult to discern much of anything, let alone a network of fine straight lines.

In 1962, American astronomer Earl Slipher published a book filled with photographs of Mars from between 1905-1961. Slipher worked with Percival Lowell at the Lowell Observatory and was a long-time proponent of the Martian Canals.

In 2002, authors William Sheehan and Thomas Dobbins wrote an article about Percival Lowell's observations of Venus in Sky & Telescope Magazine. Soon thereafter, Sheehan and Dobbins were contacted by several ophthalmologists who pointed out that Lowell's "spoke system" bore a striking resemblance to the inside of an eye. This explanation was later explored in reference #44.

Authors William Sheehan and Thomas Dobbins hypothesize that Lowell accidentally converted his telescope into a large ophthalmoscope by severely "stopping down the aperture of his telescope".

Italian astronomer Giovanni Riccioli observed a band of color on the disc of Venus on January 9, 1643. The dayside was rubicund (reddish), the terminator was flavescent (yellowish), while the nightside had a cerulean (greenish-blue) hue. Riccioli ascribed the vivid colors to light being refracted inside his telescope. Riccioli also witnessed a semicircle of bright light enclosing the nightside of Venus. This is known as limb brightening and is caused by atmospheric refraction of sunlight. See reference #22 for other examples of this. Riccioli is typically recognized as the person who discovered the Ashen Light but that credit should in all probability go to Athanasius Kircher. See reference #46.

In 1660, German Jesuit scholar and polymath Athanasius Kircher recounted Giovanni Riccioli's 1643 observation of a band of colors on Venus. See reference #45. Kircher had evidently observed the same multicolored light from an observatory in Palermo, Sicily, and ultimately agreed with Riccioli's interpretation that the colors arose from light being refracted inside the telescope. Kircher does not provide a date but, according to reference #47, visited Palermo in the spring of 1638. This means that the observations made by Kircher predates the one made by Riccioli by five years. The relevant passage is the italic text that begins at the bottom of page 134 and continues into page 135. See reference #46a below for some Latin to English translation attempts. This book is actually a revised and expanded edition of one of Kircher's earlier works titled "Itinerarium Exstaticum". However, Riccioli's and Kircher's observations of Venus is only mentioned in this revised edition titled "Iter Exstaticum".

Author John Fletcher wrote extensively about Athanasius Kircher and documented much of his vast body of work. After passing away in 1992, this book was posthumously published by his wife Elizabeth in 2011. It is primarily comprised of a thesis written by Fletcher in 1966. According to Fletcher, Kircher visited Palermo in the spring of 1638 while on his way from Malta to Rome. After returning home, Kircher was "never to leave Rome again". Just to be certain, I reached out to two historians and both of them confirmed that Kircher did indeed visit Palermo in 1638 and that this is the only time he is known to have done so.

French astronomer André-Louis Danjon observed the Ashen Light on multiple occasion and was confident that it was an optical illusion. See reference #22 for a detailed breakdown of the Ashen Light debate.

When Venera 9 began to orbit Venus in late October of 1975, the onboard spectrometer detected bursts of light on the planet's nocturnal hemisphere. These findings are examined in chapter 15 by Vladimir Krasnopolsky, an expert on spectroscopy and planetary atmospheres. Krasnopolsky ultimately ascribed the flashes to powerful lightning strikes within the atmosphere of Venus. The whole chapter is pertinent but the possibility of lightning is primarily examined in section four, beginning on page 478.

Like many other astronomers of his age, Scottish astronomer James Ferguson believed that all the planets in the Solar System were inhabited. The quote about Mercurians can be found on page 9.

William Herschel elaborates on his "habitable sun" hypothesis. One notable addition is that the solar inhabitants are now insulated from the blazing outermost layer of the luminous atmosphere by intermediate layers of "planetary clouds".

A brief review of William Herschel's "habitable sun" hypothesis.

Scottish astronomer Alexander Wilson observed that sunspots become increasingly concave as they approach the limb of the Sun. This led Wilson to conclude that sunspots are "vast excavation[s] in the luminous matter of the Sun" which revealed the cool "nucleus" underneath. This phenomenon has since been dubbed the Wilson Effect.

This extensive lunar atlas published by Polish-German astronomer Johannes Hevelius was the first of its kind. According to reference #56, Hevelius's maps of the Moon "set a basic standard for lunar image making that was not exceeded for more than a century."

The title of this book is Latin for "Celestial Machines" and it includes detailed descriptions and illustrations of the telescopes and instruments constructed by Johannes Hevelius.

An overview of the lunar observations made by Johannes Hevelius. Hevelius could discern "seas, bays, islands, continents, peninsulas, capes, lakes, swamps, rivers, plains, mountains, and valleys" upon the Moon. He also believed it to be inhabited by intelligent beings but was never fortunate enough to observe these "Selenites" as he called them. Also, citation 19 of chapter 11 (regarding a quote by Hevelius) has been incorrectly attributed to page 353 of reference #54. It's the correct book but the quoted passage appears on pages 118-119 instead.

This is an English translation of a treatise about the Moon written by Plutarch in the 1st century CE. Plutarch repeatedly describe the lunar maria (the dark regions on the Moon's surface) as "seas" and "oceans".

Pages 6-7 and 22 explain how bright and dark regions on the Moon came to be regarded as continents and oceans respectively. It's interesting to note that some thought it was the other way around, light regions being vast bodies of water interrupted by dark spots of land. Pages 109-110 provides a brief overview along with a few sketches of Franz von Gruithuisen's discovery of a "lunar city".

The modern lunar nomenclature was first proposed by Giovanni Riccioli in 1651 in reference #45. Thousands of additional features have since been named and all of them can be found on this page collaboratively maintained by the International Astronomical Union, United States Geological Survey, and NASA.

The 39th chapter of this encyclopedia about volcanoes covers "The Volcanism On the Moon". This is the second edition. The first edition was published in 1999.

The letter quoted in the video is titled "Letter from Mr. Herschel to the Reverend Dr. Maskelyne, Astronomer Royal". While the letter is dated June 12, 1780, much of the text was written in December 1778.

William Herschel never publicly acknowledged his belief in Lunarians but revealed in his private notes and correspondence that he spent years searching for them. This is the second edition. The first edition was published in 1986. The quote about "circuses" on the Moon can be found on page 65. The word circuses means "circular structure" in this context.

Franz von Gruithuisen presented his case for an inhabited Moon in this 1824 book titled "The Discovery of Many Distinct Traces of Lunar Inhabitants, Especially of One of Their Colossal Artificial Buildings". The book is divided into three sections concerning traces of vegetation, animals, and artificial structures that Gruithuisen is supposed to have witnessed on the Moon. Gruithuisen reported similar findings both before and after the publication of this book across multiple journals and papers. The passages quoted in the video were taken from pages 42 and 110 and were human-translated.

A comprehensive overview of Franz von Gruithuisen's discovery of a "lunar city".

The landform described as a "lunar city" by Franz von Gruithuisen in reference #63 can be seen near the bottom right of this photograph of the Moon. The approximate coordinates are: 6.00, -7.50. It's similar to the "face" on Mars of reference #95 in that it's only visible under very specific circumstances when the Sun is very low in the lunar sky.

The Great Moon Hoax made its debut in The Sun newspaper on August 28, 1835, and consisted of six separate articles. Scans of these articles do not appear to be available online but, due to their extreme popularity, the whole series was reprinted in this pamphlet form later that same year. The story is written from the perspective of John Herschel's supposed assistant "Dr. Andrew Grant". Grant was not a real person but invented by Richard Locke. The quote in the video can be found on pages 20-21.

This whole book is dedicated to the Great Moon Hoax but chapters 12, 13, and 16 are the most pertinent. Author Matthew Goodman stresses that the story written by Richard Locke had "not been intended as a hoax at all; it had been intended as a satire". Regardless of Locke's intentions, his story managed to deceive thousands around the world all the same.

The founder of The Sun newspaper, Benjamin Day, ultimately confessed that he paid Richard Locke to fabricate the story.

The egg-shaped Moon hypothesis originated with this abstruse paper by Danish mathematician and astronomer Peter Hansen. It is written in French and is highly technical so I've only included it here for the sake of completeness. See reference #72 for an uncomplicated overview.

An overview of the egg-shaped Moon hypothesis.

John Herschel expressed support for the egg-shaped Moon hypothesis and, by extension, lunar inhabitants in the fifth edition of this book. See articles 436a and 436b on the specified pages. The first edition was published in 1849.

This anonymous account of the egg-shaped Moon hypothesis was "almost certainly" written by John Herschel according to sources like reference #76 among others. The quote in the video can be found on page 549.

A brief overview of the egg-shaped Moon hypothesis as it relates to John Herschel.

Canadian-American mathematician and astronomer Simon Newcomb was among the most vocal critics of the egg-shaped Moon hypothesis first proposed by Peter Hansen in reference #71.

This episode of an American science fiction series from the mid-1950s is about an astronomer named Laurence Kerston who discovers evidence of extraterrestrials on the Moon. After photographing the Moon using a new type of camera, Kerston detects a halo of radioactive dust that appears to emanate from the farside of the Moon. Another set of photographs reveal a formation of spaceships as they approach and depart the Moon's hidden hemisphere. An unmanned rocket is launched by the US military to investigate. Upon reaching the farside it mysteriously malfunctions and crashes into the Moon. The episode ends with Kerston and other scientists realizing that aliens must be using the other side of the Moon as a dumping ground for radioactive waste.

Many science fictions stories before 1959 took advantage of our inability to see the farside of the Moon to populate it with intelligent inhabitants. These are but three examples.

This book is a "translation, extension, and revision" of a book originally written in Russian by astronomer Iosif Shklovsky. It is a collaborative project between Shklovsky and Carl Sagan. As outlined in the preface, the sections delimited by the symbols ᐁ and ᐃ were specifically written by Sagan.

Information about and photographs from the Soviet Luna 3 (Луна-3) mission. The probe was also known as "Lunik III", "Automatic Interplanetary Station", and "E-2A No.1".

Everything you could possibly want to know about the Luna 3 mission can be found in this technical document. This is a NASA commissioned translation of the original Soviet publication from 1960.

Boris Belitsky was a radio journalist and science correspondent for a popular radio station known as Radio Moscow. In this article, he stated that the final images transmitted by Phobos II depicted features either on or above the surface of Mars which he described as "quite remarkable", "spindle-shaped", and "intriguing and puzzling". Belitsky was also a double agent who was recruited by the American CIA but secretly remained loyal to the Soviet KGB.

According to Alexander Dunayev, an image taken by Phobos II included an "odd-shaped object between the spacecraft and Mars". Dunayev was the chairman of Glavkosmos, a subsidiary of the Soviet space program, who oversaw the Phobos II mission. He also stressed that, while they could not identify the object, it was probably some kind of debris.

Marina Popovich was a decorated Soviet Air Force pilot who often spoke about her experiences with UFOs. In 1991, she held a press conference at the Russian Consulate in San Francisco where she revealed a photograph taken by Phobos II depicting a "pencil-like object".

Many of the more egregious claims about the so-called "Phobos Incident" originated with this book by pseudohistorian Zecharia Sitchin. While not all sources agree on the specifics, the overall story goes something like this. Soviet mission control lost contact with Phobos II in late March of 1989. The last photograph transmitted back to Earth depicts an unknown pencil-shaped object near the moon Phobos. This is said to be an alien spaceship which disabled Phobos II. Other images depicts a vast elliptical shadow on the surface of Mars. This is said to be the shadow of the alien spaceship. While this edition of the book was published in 2002, it was first printed in 1990 when information about the Phobos II mission was extremely limited.

This is a recording of the Soviet evening newscast Время (Time) originally broadcast on March 29, 1989. At the specified timecode, a segment about Phobos II features interviews with Soviet scientists as well as images transmitted by the probe. The scientists express confusion about the shadow cast upon the surface of Mars and the news correspondent jokingly asks them whether it could be the contrails of a rocket taking off from the surface. See reference #87a below for a Russian to English translation of this segment.

General information about Phobos II with links to the raw data transmitted back to Earth.

A detailed explanation of the Phobos Incident.

A succinct overview and debunking of the Phobos Incident.

Scientists from Glavkosmos who worked on the Phobos II mission explain why the shadow of Phobos appeared elliptical in images captured by Phobos II. M. K. Naraeva, A. S. Selivanov, and V. D. Kharlamov, who are listed as authors of this paper, appeared in the newscast of reference #87.

Scientists from the Institute of Space Device Engineering in Moscow explain why the shadow of Phobos appeared elliptical in images captured by Phobos II.

Numerous spacecraft have captured the shadow of Phobos whilst photographing the surface of Mars. Below are two examples of such photographs. The first was taken in 1999 by NASA's Mars Global Surveyor. The second was taken by ESA's Mars Express in 2005.

The Soviet space probe Zond 3 took multiple photographs of the Moon back in 1965. One specific copy of one of these photographs appears to show a "tower" on the Moon. It's unclear when and where this copy first appeared.

The "face" on Mars was first spotted in an image taken by the Viking 1 orbiter in 1976. It's a textbook example of pareidolia. It's merely an illusion caused by the happenstance of light and shadow. The face evaporates when the Sun is positioned at a less oblique angle.

There are at least two features on Mars which have been described as a "monolith" but there are literally thousands of other boulders of equal or even greater size dotting the Martian surface.

The Phobos Monolith was discovered around the turn of the millennium in a photograph taken by the Mars Global Surveyor in 1998. It's also visible in two images taken by the Mars Reconnaissance Orbiter in 2008.

Nikola Tesla chronicled the enigmatic radio signals he received at his Colorado Springs laboratory in various letters and articles. He made no secret of the fact that he believed them to be interplanetary messages. By 1901, the story had been widely publicized and Tesla summarized the whole ordeal in this magazine article.

Chapter 25-26 provide a detailed overview of the radio signals received by Nikola Tesla while he was conducting wireless radio experiments at his Colorado Springs laboratory in 1889. According to author Marc Seifer, Tesla might have intercepted a transmission from one of the other radio pioneers active at the time. Most notably, his European rival Guglielmo Marconi. Seifer speculates that Marconi might have transmitted the letter S in Morse Code (represented by three clicks) across the English Channel on the same day that Tesla is supposed to have first received the signals. However, according to reference #101, Tesla and Marconi were operating on different frequencies and it's doubtful that Marconi's signals were powerful enough to cross the Atlantic.

The section titled "An Interplanetary Message?" of chapter 13 provides a brief overview of the radio signals received by Nikola Tesla while he was conducting wireless radio experiments at his Colorado Springs laboratory in 1889. Author Bernard Carlson rejects the solution proposed in reference #100 and supports the hypothesis offered in reference #108.

According to this letter which Nikola Tesla sent to the Red Cross Society in 1900, the enigmatic radio signals consisted of a repeating sequence of three pulses. He described the pattern as "one... two... three...".

In this article, Nikola Tesla stated that the radio signals he received more than two decades prior consisted of four distinct pulses. He described the pattern as "1-2-3-4". He made a similar remark is an unpublished interview in 1935 which is quoted in reference #108.

More than two decades after Nikola Tesla received pulsed radio signals at his Colorado Springs laboratory, he was still convinced that it had been an "interplanetary communication". While he was initially uncertain about its origin, he had since determined that the signals must have emanated from Mars.

During a celebration of his 81st birthday in New York, Nikola Tesla announced that he was in the process of developing a technology capable of interstellar communication. It's unclear what technology Tesla was talking about as he failed to disclose any technical details. He ambiguously stated that it would make it possible to convey "several thousand units of horsepower to other planets, regardless of the distance." Tesla did nonetheless express remarkable confidence in his new creation by stating that "this discovery of mine will be remembered when everything else I have done, is covered with dust." He also expected this invention to grant him the Pierre Guzman prize of reference #35 and declared that "life on other planets is an infinite probability, a certitude."

The Pierre Guzman Prize of reference #35 was awarded to the crew of Apollo 11 in Paris on December 8, 1969. Neil Armstrong, Buzz Aldrin, and Michael Collins received gold medals instead of money. The event received surprisingly sparse media coverage.

Planets like Jupiter and Saturn are known to emit radio signals. These emissions are "characterized by their impulsive or pulse-like nature" which is consistent with Nikola Tesla's description. The authors of this papers actually rebuilt the receiver used by Tesla and ultimately concluded that "it is entirely within reason to identify Tesla's signals as the detection of [radio] emissions originating from Jupiter."

This paper examines all the available evidence for lightning on Venus. The authors cast some doubt on the popular interpretation that Venera 9 detected lightning. Instead they speculate that the flashes "may have been caused by light reflected from some material released from the spacecraft". Nevertheless, data gathered by subsequent missions are less controversial and, while the authors fall short of determining that lightning does occur on Venus, they acknowledge that much of the evidence is "fully consistent" with that conclusion.

Data gathered by JAXA's Akatsuki spacecraft has detected tentative signs of lighting on Venus. The spacecraft is outfitted with a Lightning and Airglow Camera (LAC) specifically designed for this purpose.

According to this paper, in order for lighting to to be responsible for the Ashen Light "there must be approximately 1000 flashes per second within the clouds on the night side". The paper also states that this would be "about 10 times the number of ground-to-cloud flashes on Earth's nighttime hemisphere" but this is based on now obsolete data. See reference #112 for more recent figures.

According to this paper, there are 46 lighting strikes on Earth every second. Previous estimates of the "mean global flash rate" were significantly higher. Many sources (even to this day) quote a figure from 1925 which estimated the mean global flash rate at 100 lighting strikes per second.

Based on data gathered by various probes and landers, the authors of this paper tried to determine whether flashes of light on Venus could be ascribed to lightning. As to whether these flashes could be responsible for the Ashen Light, the authors found "no support" for this conclusion as the flashes were too faint to be visible from Earth.

A brief description of aurorae, also known as the Northern Light (aurora borealis) or the Southern Lights (aurora australis).

As described in this article, Venus does not have an "intrinsic" magnetic field but "the interplanetary magnetic field carried by the solar wind piles up above the planet’s upper atmosphere, creating a weak magnetic envelop around Venus".

The detection of oxygen green-line auroral/airglow emissions on Venus received a lot of media attention after the publication of this peer-reviewed paper. The paper is quite technical but see reference #118a and reference #118b below for more plain-spoken overviews. See also reference #22 for a more detailed explanation and an attempt to link these findings to the Ashen Light.

This whitepaper, which advocates for more missions to Venus, provides a decent overview of various atmospheric phenomena on Venus, including emissions that are analogous to terrestrial airglow and aurorae.

This abstract of a presentation about the oxygen green-line auroral/airglow emissions provides a brief yet succinct overview. The phenomenon is described as "a bright auroral line [...] detected on the Venusian nightside after major solar storms as a diffuse, global aurora".

While far less certain than the watery past of Mars, it's possible that Venus, too, was once covered by a vast ocean.

This paper regarding the detection of phosphine in the atmosphere of Venus made a lot of headlines at the end in 2020. Phosphine is a gas associated with living organisms and is thus a potential biosignature. But subsequent research, such as reference #123, has cast serious doubts on these results so there is more work to be done.

There's a lot of evidence to suggest that, billions of years ago, the surface of Mars was covered by water.