The 'oldest unsolved mystery' in observational astronomy
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How could it be that a straightforward observation about another planet in our solar system could evade scientific explanation for 400 years? The “Ashen Light” of Venus, a ghostly emission of light from the night side of our nearest planetary neighbor, is still not fully understood. Mystery Of The Ashen Light of Venus shows how humanity may be closing in on a definitive interpretation of its existence and cause.
Readers of popular science books often love a good mystery, especially one that has managed to resist the explanatory powers of science for so long. The narrative follows the forward march of history, but with enough diversions into detail on certain topics to keep the flow lively and interesting with an intent to convey a sense of why the subject has captivated so many astronomers — both professional and amateur. Out Now on Springer Astronomers' Universe On the cover: An eyewitness impression of a 1962 daylight Ashen Light sighting by famed planetary scientist and space artist William K. Hartmann. |
REVIEWS
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"Keep an open mind when you read this book and, if you are a Venus observer, come to your own conclusion. You may be surprised." -The Planetarian, Vol. 50, No. 3. (September 2021)
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"Every astronomer should read Mystery of the Ashen Light of Venus and do their own observations of the planet. Maybe we can add more evidence to this 400-year old astronomical mystery." -Mike Weasner, Cassiopeia Observatory
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CONTENTS
1. Introduction
A brief overview of the topic of the book, how I came to write about it, and what the book aims to achieve.
2. Prologue: The Martians that Never Were
The book opens with the story of another Solar System world and a case of questionable perception by Earth-bound astronomers that leads to some of the same questions we encounter in trying to understand the Ashen Light. The West’s fascination with Mars in the last quarter of the nineteenth century was launched after one highly reputable (but "severely myopic" and color blind) astronomer declared that he had seen through his telescope the signs of structures that seemed deliberately designed and constructed. A ‘Martian canal’ craze ensued that garnered support from the scientific community but was ultimately proved utterly false. The need for careful investigation and adequate skepticism in evaluating extraordinary claims clashes with a tendency to see what others (claim that they) see sets the stage for examining similarly grandiose observations of Earth’s nearest planetary neighbor.
3. 'I could see the dark part of Venus…’
This introductory chapter sets up the phenomenon of the Ashen Light for those unfamiliar with the astronomical history, and gives an overview of the investigation in the book. It begins with a brief history of the observation of the planet Venus, from antiquity through the invention of the astronomical telescope in Europe during the early years of the seventeenth century. The basic phenomenology of the Ashen Light is reviewed, including a basic distinction between its so-called ‘positive’ and ‘negative’ forms. It introduces an extensive assembly of hundreds of observations of the Ashen Light from 1643 to the present day and points out correlations with certain physical influences that provide some initial insight as to the possible mechanisms that might explain it. The chapter aims to both summarize the topic of the book, as well as to draw the reader progressively deeper into important elements of the apparent mystery.
4. First Light: Early Accounts of the Ashen Light 1643−1800
The history of the Ashen Light formally begins with its first reported observation in 1643. Nearly all early accounts are described, appealing to primary sources wherever possible. The narrative captures the wonder and puzzlement of early observers, who often did not trust their own eyes. The rarity of Ashen Light appearances in this time is evident from the few available accounts and apparent independence of observers who reported they saw it, lending credence to the notion of a real but infrequent phenomenon. This recounting of observations in the seventeenth and eighteenth centuries is framed against the developments generally in the equipment, observing techniques, and (emerging) scientific thinking of astronomers during the same period.
5. Going Mainstream: A Scientific Approach c. 1800−1900
The Ashen Light story continues into the nineteenth century. Observers begin to bring a sense of scientific skepticism to their increasingly systematic scrutiny of Venus, even while various authors treat the Ashen Light as a real, but rare, phenomenon that might be telling is something about physical conditions on Venus. Astronomers continue to search for answers, limited by the pace of astronomical thought and technology development. The evolution of thinking on this subject is juxtaposed against Victorian attitudes about science, rapidly advancing frontiers of astronomy, and an evolving picture of Venus.
6. What is the Light? Historical Explanations of the Ashen Light
As astronomy evolved into astrophysics during the late nineteenth and early twentieth centuries, observers and theorists alike came to gradually accept some basis in reality for the Ashen Light and began to search for plausible physical explanations. One by one, these explanations are considered, including the reflected light of the Earth and stars, a phosphorescent atmosphere or surface, and even the possibility that the Ashen Light results from the activities of a race of intelligent Venusian beings. Each is examined in turn along with the thinking that produced it and evidence both for and against. As the twentieth century dawns, some feel that the mystery will never be fully solved, but indications exist that hint at the probable correct answer.
7. Venus as a knowable world: Chasing the Ashen Light into the Space Age 1900–1980
The twentieth century saw the planets change from distant visions in ground-based telescopes to real places with properties humans could sense and measure firsthand from orbiting and landing spacecraft. While up-close observations knocked out some potential physical explanations for the Ashen Light, reported sightings increased, particularly after the Second World War as more people took up amateur astronomy as a leisure activity. Particularly strong “outbreaks” in 1953 and during the International Geophysical Year (1957-58) are described. Finally, recent scientific work is recounted that offers particular physical insight into perhaps the most likely physical explanation left standing: an auroral-like process in the Venusian atmosphere.
8. New ideas for an old problem: Observations and science 1980–2020
The golden age of the exploration of Venus by spacecraft arrives with the U.S. Pioneer Venus and Soviet Venera missions alongside a renewed interest in coordinated Ashen Light observations on Earth. New data narrow the range of possible explanations for the phenomenon, including lighting and active volcanoes. But the evidence increasingly implicates atmospheric physics that excite the green glow of light emission from oxygen atoms in the Venusian lower ionosphere. A plausible case for this glow as the Ashen Light is presented based on the latest observations and theoretical models.
9. Seeing what we want to see: The psychology of the Ashen Light
This chapter concerns two instances in the history of astronomy in which faith in the authorities of science was validated or contradicted. In both cases, a psychology that fundamentally trusts the input of the senses is examined critically in the context of a growing certainty in the 19th century that humanity's understanding of the physical nature of the universe was near its zenith. In one example, the discovery of the planet Neptune, the predictions of classical gravitational theory were corroborated, while in another, the failure to find the conjectural planet 'Vulcan', a taste of new physics was suggested. The results suggest that both factors are at work in how the astronomical world has wrestled with the problem of the Ashen Light, including the uncomfortable possibility that the Ashen Light is something like a collective hallucination, the result peer pressure to acknowledge the existence of something that was never real in the first place.
10. Perception revisited: The psychophysics of the Ashen Light
Here the faint limits of human vision, the role of contrast effects in the visual detection of faint-light phenomena, and optical aberrations that may lead observers astray are explored: perhaps the brain is sometimes tricked into sensing light that simply isn’t really there. The likelihood of visual detection of the light on Earth is examined through the lens of vision science and what it can (and can't) tell us about the reality of what our senses present. Finally, I confront an outcome in which we might hold the Ashen Light to be simultaneously real and illusory, consigning it to a future in which the problem it represents is never fully solved.
11. Epilogue: Evanescence and Evasion
Is it real or imagined? I acknowledge a phenomenon real ‘enough’ to beguile astronomers for almost four centuries and persist despite the repeated inability of observers to create a wholly objective record of its existence. The result stands out from every other formerly-unsolved mystery of astronomy history, leaving an impression on the reader of a curiosity that endures. Nevertheless, I reach some conclusions that consider the validity of all of the explanations of the Ashen Light, both real and imagined, and speculate on a future in which the Ashen Light never completely disappears from observers’ reports.
1. Introduction
A brief overview of the topic of the book, how I came to write about it, and what the book aims to achieve.
2. Prologue: The Martians that Never Were
The book opens with the story of another Solar System world and a case of questionable perception by Earth-bound astronomers that leads to some of the same questions we encounter in trying to understand the Ashen Light. The West’s fascination with Mars in the last quarter of the nineteenth century was launched after one highly reputable (but "severely myopic" and color blind) astronomer declared that he had seen through his telescope the signs of structures that seemed deliberately designed and constructed. A ‘Martian canal’ craze ensued that garnered support from the scientific community but was ultimately proved utterly false. The need for careful investigation and adequate skepticism in evaluating extraordinary claims clashes with a tendency to see what others (claim that they) see sets the stage for examining similarly grandiose observations of Earth’s nearest planetary neighbor.
3. 'I could see the dark part of Venus…’
This introductory chapter sets up the phenomenon of the Ashen Light for those unfamiliar with the astronomical history, and gives an overview of the investigation in the book. It begins with a brief history of the observation of the planet Venus, from antiquity through the invention of the astronomical telescope in Europe during the early years of the seventeenth century. The basic phenomenology of the Ashen Light is reviewed, including a basic distinction between its so-called ‘positive’ and ‘negative’ forms. It introduces an extensive assembly of hundreds of observations of the Ashen Light from 1643 to the present day and points out correlations with certain physical influences that provide some initial insight as to the possible mechanisms that might explain it. The chapter aims to both summarize the topic of the book, as well as to draw the reader progressively deeper into important elements of the apparent mystery.
4. First Light: Early Accounts of the Ashen Light 1643−1800
The history of the Ashen Light formally begins with its first reported observation in 1643. Nearly all early accounts are described, appealing to primary sources wherever possible. The narrative captures the wonder and puzzlement of early observers, who often did not trust their own eyes. The rarity of Ashen Light appearances in this time is evident from the few available accounts and apparent independence of observers who reported they saw it, lending credence to the notion of a real but infrequent phenomenon. This recounting of observations in the seventeenth and eighteenth centuries is framed against the developments generally in the equipment, observing techniques, and (emerging) scientific thinking of astronomers during the same period.
5. Going Mainstream: A Scientific Approach c. 1800−1900
The Ashen Light story continues into the nineteenth century. Observers begin to bring a sense of scientific skepticism to their increasingly systematic scrutiny of Venus, even while various authors treat the Ashen Light as a real, but rare, phenomenon that might be telling is something about physical conditions on Venus. Astronomers continue to search for answers, limited by the pace of astronomical thought and technology development. The evolution of thinking on this subject is juxtaposed against Victorian attitudes about science, rapidly advancing frontiers of astronomy, and an evolving picture of Venus.
6. What is the Light? Historical Explanations of the Ashen Light
As astronomy evolved into astrophysics during the late nineteenth and early twentieth centuries, observers and theorists alike came to gradually accept some basis in reality for the Ashen Light and began to search for plausible physical explanations. One by one, these explanations are considered, including the reflected light of the Earth and stars, a phosphorescent atmosphere or surface, and even the possibility that the Ashen Light results from the activities of a race of intelligent Venusian beings. Each is examined in turn along with the thinking that produced it and evidence both for and against. As the twentieth century dawns, some feel that the mystery will never be fully solved, but indications exist that hint at the probable correct answer.
7. Venus as a knowable world: Chasing the Ashen Light into the Space Age 1900–1980
The twentieth century saw the planets change from distant visions in ground-based telescopes to real places with properties humans could sense and measure firsthand from orbiting and landing spacecraft. While up-close observations knocked out some potential physical explanations for the Ashen Light, reported sightings increased, particularly after the Second World War as more people took up amateur astronomy as a leisure activity. Particularly strong “outbreaks” in 1953 and during the International Geophysical Year (1957-58) are described. Finally, recent scientific work is recounted that offers particular physical insight into perhaps the most likely physical explanation left standing: an auroral-like process in the Venusian atmosphere.
8. New ideas for an old problem: Observations and science 1980–2020
The golden age of the exploration of Venus by spacecraft arrives with the U.S. Pioneer Venus and Soviet Venera missions alongside a renewed interest in coordinated Ashen Light observations on Earth. New data narrow the range of possible explanations for the phenomenon, including lighting and active volcanoes. But the evidence increasingly implicates atmospheric physics that excite the green glow of light emission from oxygen atoms in the Venusian lower ionosphere. A plausible case for this glow as the Ashen Light is presented based on the latest observations and theoretical models.
9. Seeing what we want to see: The psychology of the Ashen Light
This chapter concerns two instances in the history of astronomy in which faith in the authorities of science was validated or contradicted. In both cases, a psychology that fundamentally trusts the input of the senses is examined critically in the context of a growing certainty in the 19th century that humanity's understanding of the physical nature of the universe was near its zenith. In one example, the discovery of the planet Neptune, the predictions of classical gravitational theory were corroborated, while in another, the failure to find the conjectural planet 'Vulcan', a taste of new physics was suggested. The results suggest that both factors are at work in how the astronomical world has wrestled with the problem of the Ashen Light, including the uncomfortable possibility that the Ashen Light is something like a collective hallucination, the result peer pressure to acknowledge the existence of something that was never real in the first place.
10. Perception revisited: The psychophysics of the Ashen Light
Here the faint limits of human vision, the role of contrast effects in the visual detection of faint-light phenomena, and optical aberrations that may lead observers astray are explored: perhaps the brain is sometimes tricked into sensing light that simply isn’t really there. The likelihood of visual detection of the light on Earth is examined through the lens of vision science and what it can (and can't) tell us about the reality of what our senses present. Finally, I confront an outcome in which we might hold the Ashen Light to be simultaneously real and illusory, consigning it to a future in which the problem it represents is never fully solved.
11. Epilogue: Evanescence and Evasion
Is it real or imagined? I acknowledge a phenomenon real ‘enough’ to beguile astronomers for almost four centuries and persist despite the repeated inability of observers to create a wholly objective record of its existence. The result stands out from every other formerly-unsolved mystery of astronomy history, leaving an impression on the reader of a curiosity that endures. Nevertheless, I reach some conclusions that consider the validity of all of the explanations of the Ashen Light, both real and imagined, and speculate on a future in which the Ashen Light never completely disappears from observers’ reports.
Gallery of Images
©2021 John C. Barentine (except as noted), all rights reserved.