Johann Schröter, William Herschel
and the Mountains of Venus: Overview

By Andrew James

[ The original paper produced here, first appeared in the Royal Astronomical Society of New Zealand (RASNZ) journal in March 2003 (Southern Stars 42, 1, March (2003). It covers the period when questionable observational phenomena was observed on Venus by several astronomers of the time, much of which, was focused on the observations made by German astronomer, Johann Schröter. It is reproduced with kind permission of the RASNZ, which I requested after a number of enquires from some noted planetary observers who did not have general access to the original published article. ]

[Andrew James : April 2005.]


Since the invention of the telescope the observations of atmospheric phenomena regarding Venus have always proved difficult. Some early observers reported variations in the curvature of the cusps and so-called terminator anomalies. It was these particular anomalies and their interpretation that lead to a somewhat passionate debate, mainly between Friedrich Wilhelm (later William) Herschel (1738-1822) and his fellow compatriot Johann Heironymous Schröter (1748-1816). Schröter assumed that the direct cause of the irregularities, especially near the southern cusp, was a mountain or a mountain range — a Venusian Himalayas, while Herschel concluded the alleged cause of the Schröters Venusian anomalies could possibly be attributed to Schröters tarnished speculum mirror. This paper also discusses the life and observations of Schröter, and attempts to explain the basis of his reputation as a poor and unreliable observer.


Two factors influence this problem — the brightness of Venus and its proximity to the Sun as seen from the Earth. In the early days of observational astronomy the early evening and morning twilight hours were considered the best times since its apparent brilliance was reduced but with the disadvantage of the planet being close to the horizon. In addition, daylight observations were limited by speculum metal mirrors that were impossible to use during the day due to their thermal expansion. Early observations made with refractors were not very common — likely limited by light scattering and inadequate baffling.

Since the 1870s, the advent of glass mirrors has made it possible for useful observations of Venus during full daylight. Today observations are often made during the daytime.

Origin of the Mountains of Venus

Observations of spots visible on the Venusian cloud tops were first described in 1643 by Franceso Fontana (1602-1656) from Naples, Italy. Two years after this discovery, Fontana again reported some darker spots, that were later confirmed in 1666 and 1667 by the brilliant French observer Giovanni Domenico Cassini I (Jean Dominique Cassini) (1625-1712).

The origin of any discussion on possible mountains on Venus is from the interpretations of various limb projections seen by these early observers. According to Baum (2001), the first recorded interpretation of these effects was reported by Phillipe de la Hire in 1700 to the Paris Academy, who declared;

Montage beaucoup plus grandes que celles de la Lune, qui le font plus â proportion que celles de la Terre.

Many mountains far higher than those of the Moon, and greater in proportion than those of the Earth (Baum, 2001)

Later Nicolas Camille Flammarion (1842-1925) came to the same conclusion. [1] Both attributed the visibility of these spots as telescope imperfections. Some sources since have all attribute these phenomena as poor atmospheric seeing.

Other types of features were also seen on Venus. In Paris, Phillipe de la Hire, 1640-1718 (1700) he also noted dark spots in August 1700, but also noticed that there were;

…greater inequalities in the termination of the light of Venus, than the Moon. (Schröter, 1795), (Baum, 1973)

These terminator inequalities, also known as the Venus Contour Anomaly, were first seen by Fontana (1643) and Burratini (1666), who described the terminator as raggedness. (Baum, 2001) Johann Schröter, also noted historically that this terminator phenomenon was again reported by Bianchini in 1726. For many years these observations of Fontana, Burratini, de Le Hire, Cassini and Bianchini were considered to be oddities.

The question about the cause of these deviations in Venus terminator shape escalated with the famous clash between the two great observational titans — the planetary discoverer of Uranus, William Herschel and the German lunar and planetary specialist Johann Schröter.

At first using a 3-ft long achromatic refractor, between 1779 and 1793 Schröter admitted he saw little in regards any evidence of structured features except that the terminator gradually decreased in brightness. Herschel said he saw nothing.

Using his larger 7-ft long Herschelian telescope in perfect seeing conditions at 5pm on the 28 December 1789, Schröter reported seeing a bright circular point of light within the darkened disk of Venus. Increasing the magnification to 370×, this illuminated point became clearly separated from the southern terminator of the planets disk. Again on 25 December 1791 he saw this same brilliant starry point near the southern cusp. Upon some serious pondering, Schröter convinced himself this was no optical aberration and started to postulate about the true cause of the phenomena. By the beginning of 1792 he had reasoned that the only logical explanation was the reflection of light from a tall mountain range or peak — arguing from the similarity to the circumstance that we sometimes see on the surface of the Moon. These hypothetical mountains affected the southern cusp of Venus, and according to Florens Fredrick Chaladni (1756-1827), Schröters argument roughly followed the lines, that if the Venusian surface was level, then the horns of the crescent would be even. In Schröters own words, he said of his observations in March and April 1790 ;

…one cusp frequently appears pointed and the other blunt, owing to the shadow of some mountain darkening the extremity of the latter…

Another quote of Schröters, according to Baum (2001) was also announced to the Royal Society in London in 1792;

… [mountains] of such enormous height, as to exceed 4, 5, or even 6 times the perpendicular elevation of Cimborano, the highest off our mountains. (Baum 2001)

On hearing of these presumed Venusian mountains, Herschel in 1792 began criticising Schröters interpretation of their origin. Perhaps Herschel was correct in this view, but in these times, Schröter himself was to be seen as the leading authority in observational astronomy regarding any Venusian atmospheric phenomenon. We should also remember such speculative views were more liberally accepted among the astronomical community of this era. In retrospect, the mountains to which he was referring, likely originated from de la Hire statements. It was likely his observation of the 28th December 1789 started to change his view of the reality of de La Hires Academy claims. Yet again, on 25 December 1791 Schröter reported seeing similar limb projection phenomena. After the publication of his views, what happened next was something likely unexpected from the astronomical community — Schröter had to defend his observations and interpretation. [2]

After the Royal Society announcement in 1792, Schröter continued to sporadically see and report these effects throughout the 1790s, backed quietly by his assistant Karl Ludwig Harding (1765-1834) who also noted and confirmed the phenomena. Harding was also a noted keen observer and later became the Professor of Astronomy at the German University of Göttingen and went on to discover the asteroid Juno during March 1804. This support proved to be an important lever against the increasing criticism.

The Dichotomy of Venus

Another mystery associated with Venus is the so-called Schröter Effect — based on the problem of the observed time of the Venusian Dichotomy. In August 1793, Schröter had discovered that the observed time of the 50% phase did not correspond to what they predicted, and seeing some deformity of the southern limb remaining concave for up till eight days before or after conjunction with the Sun. He thought the average difference in dichotomy was six days, and some references still wrongly states eight days, though modern values — based on several dichotomies — suggested perhaps four days early or late, depending on the side of the particular elongation. Some even suggest that this is merely an optical illusion, yet it is odd that the effect is neither aperture, field orientation nor magnification dependant. A proof, in a partly unconvincing argument of this optical effect was presented in Sky and Telescope in August 1994; some 201 years later! A proper explanation of the effect has yet to be determined.

Schröter’s Lunar Observations

Schröters vigorous interest for some twenty-eight years was the observation of the Moon. In that era popular beliefs of the day held that the Moon and all other planets might be inhabited. Like Herschel, Schröter thought this might be true. Starting serious lunar observing in 1779, Schröter discovered many lunar features and made thousands of drawings According to some. Schröter was not a good draughtsman, and his drawings both disorganised and crude, based on the small part of his work which remains. King (1955) further says of his complete ardour for the subject, he was; …a persistent lunar and planetary observer. Unlike his predecessors, he made several useful repeated observations of different aspects of the same lunar features throughout the lunar month. From this he could estimate the heights of lunar mountains and the general topography of the lunar terrain.

Today, Schröter is often described as the Father of Selenography based on his extensive studies of the Moon. He wrote the two-volume classic book Selenotopographische Fragmente (1791 and 1802), yet he never produced a complete lunar map. [3]

Schröters first discoveries were of the lunar features known as clefts - to the eye seemingly long cracks in the lunar surface. One of his most famous discoveries was Rupes Recta, commonly called the Straight Wall which lies within Mare Nubium. The Straight Wall extends about twenty-six (26) kilometres in length and is 250 to 300 metres in height. Spacecraft have revealed the feature has a width of some two-and-a-half kilometres, that slopes downward one side of the central edge around 8 degrees. One of the very few existing Schröters drawings is from 1781, and one remaining is of this particular feature. (Figure 1)

Another concerns the discovery of the largest of the sinuous rilles, later named Vallis Schröter (Schröters Valley). This crack, roughly two-hundred kilometre long by one kilometre deep, lies in an island complex within the mare, Oceanus Procellarum, in the north-western quadrant and hemisphere of the Moon. Vallis Schröteri starts 25km north of crater Herodotus, where the rill begins from river delta-like feature common known as the Cobras Head. From here the arc-like rill leads northward, narrowing to some 400 to 500 metres across. The end of the valley slowly losses its depth and abruptly ends near another sinuous rille. [4]

Schroter Lunar Drawing With the 
Striaght Wall

Schröters Early Life

Schröters personally was both enthusiastic and passionate, yet often appeared reserved in character. Throughout his life suffered frequent bouts of ill health. Professionally a lawyer, he became the well-respected bailiff and the community leader in the township of Lilienthal, about 150 kilometres southeast from the North Sea coast of Germany. Schröters home on the river Worp was named Amthaus, and here he built his observatory. This location later became the central meeting place of many other observers in the region — including the so-called Celestial Police. Schröter continued to be an ardent amateur astronomer all his life and financed from his own income.

In his early years, he once worked in Hannover. According to Baum (2003), Schröter association and friendship was with the Herschel family and older William, and began when he met them during several organised musical concerts. According to Berry (1898), William Herschels father had sent his son to England during the outbreak of the Seven Years War mainly because of his delicate health problems displayed during the early parts of the campaign. It is likely that Schröter understood Herschels problems, and continued corresponding with him from afar once he moved to England. Schröters observatory at Lilienthal was initially equipped with instruments from Herschel.

Schröter had a number of acquaintances and friends during this time. One of the people he personally influenced was Friedrich Wilhelm Bessel (1784-1864) when Bessel was only twenty-one years old. Bessel later went on to became the director at Königsberg Observatory in 1810.

Schröters Last Years

Schröters final years of life reads like a very sorry tale. In 1813, during the final years of the Napoleonic Wars, the French occupied and sacked Bremen under the Vandammes. The little town of Lilienthal fell into the hands of the French and was razed to the ground. Even Schröter was captured and imprisoned for a short time and the soldiers then burnt and pillaged his house and observatory, destroying much of his precious observations, manuscripts and books. Some say that the soldiers even mistook his brass telescopes for gold and pillaged them for themselves.

After this setback, Schröter had neither the finances, strength, nor the inclination to start another observatory — the reconstruction of the township was a much higher priority, and he died three years later. [5] Fortunately, most of his observational work has been discovered elsewhere, either through his letters, publications or discovery of his works posthumously. [6] [7] After 1816, the observatory fell into disrepair and finally was completely demolished in the next decade, with the observatory instruments being eventually passed on to Göttingen University. The observatory site is now marked by a small ground tablet.

Schröter died in 1816 at the age of 68 years old, the same year as Herschel was knighted by George III for his astronomical work.

Schröters efforts were later honoured by the IAU with the naming of the crater Schröter, on the edge of Mare Imbrium (Sea of Rains).

Schröters Instruments

At thirty-years-old, one of his earliest telescopes was a small Dolland telescope, a gift from Herschels brother Johann Alexander Herschel in 1779. [8] Johann Schröter already knew the Herschel family, and this telescope inspired him to greater things. As his interest grew, a larger aperture was necessary. In 1784, he bought from William Herschel a 4-foot (12cm aperture. f/13) telescope, and in 1786 a larger 7-foot (16.5cm aperture f/12.7) telescope as well as several much larger metal mirrors. This last telescope was identical to the one Herschel used to discover the planet Uranus.

Later in 1792, he turned to a German physics and chemistry professor, Johann Gottlieb Friedrich Schräder (1763-1833), of Kiel (located near the Denmark border, some 50 km north of Hamburg) for another 7-foot telescope. Again, in the same year, he purchased a 13-foot (24cm aperture f/16) telescope. Schräders telescopes also used a modified method in metal mirror making by applying gaseous arsenic and a slow cooling of the mirror, giving a more reflective surface. [9] None of these telescopes had telescope drives, and all had altazimuth mounts. It seems that both these Schräder instruments ended up being of slightly lesser quality, so Schröter eventually began constructing his own primary mirrors and telescopes with his two Lilienthal supporters (likely Harding and Olbers). According to King (1955 /1979), in November 1793, Schröter told Herschel of his constructing a 27-foot (47 cm aperture) Newtonian, [10] [11] stating;

The enterprise has been successful from first to last and with all its apparatus it is now finished. (Neison 1876)

Little is known about the observations from Schröters own telescopes, but it is fair to assume that these instruments were built for the growing interests in the systematic search for other planets and asteroids.

Schröter and the Minor Planets

After William Herschels discovery of Uranus and the famous puzzling mathematical geometric progression commonly known as either Bodes Law [12]. Schröter became the founding member and President of the Societas Liliatalica — the so-called celestial police. The original sextuplet of this group met at Schröters Observatory in Germany. They were Johann Schröter, Frederich Baron von Zack, Karl Harding, Heinrich Olbers, and possibly either Ferdinand Adolf Freiherr von Ende or Johann Gildmeister. Here the group organised a systematic search programme of the ecliptic looking for new planets.

Four months later, Giuseppe Piazzi, the head astronomer of Sicilys principal observatory, Palermo Observatory, was working on some observations for his star catalogue and discovered the first of the minor planets, Ceres, on 1st January, 1801. [12a]

At the Societys first meeting, Piazzis nomination was a natural choice for such a project because of the much better observing conditions in Sicily. It must have been disappointing to all that the introductory letter about the group had been in transit to Piazzi at his time of discovery. Once Ceres was found, it soon became lost in the solar glare, with the subsequent conjunction. At first Piazzi thought the body was merely a comet, but his uncertainty diminished as Ceres closed in on the Sun. The minor planet was later recovered by one of The Police after the conjunction, based on the intuitive orbital calculations of Karl Gauss (1777-1855), who predicted Ceres to an accuracy that placed it within a medium powered eyepiece. He was first to calculate the orbit of Ceres, so it could be recovered after its next conjunction with the Sun, and did all the positional reductions. Gauss was a frequent visitor of Schröters. The number in this group reached twenty-four after Ceres discovery.

Of all the observational planetary devices, Schröter main astronomical invention was the lucid disk micrometer, that was used to measured the physical diameters of planetary bodies. William Herschel had also made a similar device, which he first used to measured Ceres diameter in 1802. [13]

After Heinrich Wilhelm Matthäus Olbers suggested in 1803 that Ceres may be only one of many small bodies, these observers earnestly searched for more, resulting in the discovery of Juno and Vesta in 1804 and 1807, respectively.

Later, Schröter sent a letter to Heinrich Olbers stated that his observations of both Ceres and Pallas seemed unusually variable in brightness. [14] Olbers suggested ;

…these asteroids are irregular rather than round figures. (Grosser, 1982)

At the beginning of the 17th Century, Schröters work was soon quenched with the outbreak of the European Napoleonic Wars. [15] [16]

Schröters Observations of Mercury

Schröter had also observed similar irregularities in the appearance of Mercury, with respect to both surface features and of the horns of the planets cusps. During observations on the 26th March 1800 both Schröter and Harding reported seeing some features. Again, Herschel replied he could not see any surface details on Mercury. One of Schröters last observations was of Mercury in 1808, where he saw a phenomenon similar to what he was seeing on Venus — a smallish speck of light projected away from the southern limb. He also calculated that Mercurys mountain was about 18.3 kilometres in height and stated it was larger than any of the mountains on the Earth! He also estimated the axial tilt of Mercury was 20°, and suspected that he saw cloud-like patterns hiding the surface. A few years later Franz von P. Gruithuisen (1774-1852) reported seeing a similar phenomenon on 17th March 1814, in which, the southern cusp was distinctly blunt.

Schröter also once reported seeing what is now called the ashen light, although he was not the first to report this phenomenon. [18] This phenomenon consists of faint illumination on the darkened limb of the planets atmosphere or surface. It is today sometimes seen on both Venus and Mercury. In an article that appeared in Philosophical Transactions of 1795, Schröter concluded the cause of this odd brightened light might be something akin to earthshine that is sometimes seen during the times of the thin crescent Moon. This ashen light was also later seen by Herschel, Harding (1806) and by Schröter over a short period of five weeks around inferior conjunction. [19]

Schröter frequently speculated on the origins of Venus sometimes uneven and jagged terminator. These particular changes in the shape of the terminator suggested to him information on Venuss atmospheric rotation, and hence the surface rotation and he proposed the diurnal period of 23h 21m 05s. [20], [21], [22] Other astronomical events he observed, include the transits of Mercury on 3rd May 1786 and again on 5th November 1789. Several observers including Schröter, observed the effects of the aureole — the telescopic view of the planetary atmospheric haze surrounding a planets disk. Often this effect occurs during planetary transits during the disks ingress or egress against the limb of the Sun. In the case of Mercury, this was erroneously thought to be an indication that Mercury had a tenuous atmosphere.

Schröter vs. Herschel

Once Sir William Herschel, the most credible of the then known prominent observers, had heard of the alleged Venusian Mountains, he wanted them seriously and properly investigated (Herschel, 1790). Herschel boldly requested all the available observations of this …extravagance. This outburst seems very unusual against what is known and accepted about Herschels general character, as he was normally considered quite gentle and placid. Between 1792 and 1793, Herschel observationally again saw nothing, and in his detailed observation books, he kept obstinately repeating each time, and with little variation, No Mountains Visible. Among the many observations he also quotes;

As the mountains of Venus, I may venture to say that no eye, which is not considerably better than mine, or assisted by much better instruments, will ever get a sight of them; though from [the] analogy that obtains between the only two planetary globes that we compare, there is little doubt but this planet has inequalities on its surface, which maybe, for what we can say to the [contrary], very considerable.

Another highly relevant journal extract by Herschel says;

You will find that I have never been able to see any mountains on Venus; that to me the horns were always sharp.

It is possible that Herschel was only quelling the sudden rise of his more inexperienced and younger rival, but there maybe other motivations to his remarks.

In January 1783, Schröter congratulates Herschel in his discovery of Sidus Georgium; He wrote;

…it is hoped that His Majesty has presented you entirely to Astronomy and provide you with a handsome pension. Will all lovers of astronomy I wish this with my whole heart.

…the newspaper have it, to the new planet, which in Germany from the first has been called Uranus.

Thus, clearly Schröter held some admiration for Herschel, and at this time the relationship was more like a pupil to his teacher. After 1783, both Herschel and Schröter embarked along different paths in regards their observational programmes. Herschel went on to explore the realm of the stars and deep-sky, while Schröter continued on with his lunar and planetary observations.

The controversy of Herschels attacks began in early 1791, and after this time, Schröters written text is far more subdued and reflective. Whatever the reason, for sometime Herschel view of Schröter diminished. He once tersely explained the cause of the alleged observations to be attributed to Schröters tarnished speculum mirror. [23]

Herschels pursuit of Schröters observations and explanations was both vigorous and relentless. These general attacks eventually became supported by other prominent astronomers of the day, mainly because of the weight and substantial reputation of Herschel. Eventually the astronomical communitys perception was to start, especially after his death, to discredit Schröter — then the most prominent and respected visual observer in observational astronomy. His peers generally concluded that he had deceived himself into believing that Venus was both rugged and mountainous. Yet to his approbation, Schröter stayed silent but resolute, beginning several new series of micrometric measures to his observations. With time, he was unable to support his theory of the Venusian terrain with his actual observations — the essence of Herschels attack.

To some, Schröters biggest impediments were an overactive imagination and an inability to refrain from speculations that degraded the value of his observations. Modern day critics continue to harp on this flaw, especially with his drawings and observations, however, the records of his observations remaining so scant, that most are only contained in letters sent to other observers.

The attacks and comments of these discoveries continued after the death of both Herschel and Schröter. [24] For example, in 1847, Dominique François Arago (1786-1853) continued the debate as;

…une critique fort vive, et, en apparence du moins, quelque peu passionnée.
…one strong and lively criticism appears somewhat less than passionate.

Despite all this, Schröter today remains a respected amateur. Schröters legacy should also be viewed well beyond his assumed limitations as an observer.

Venusian Himalayas — Out of Vogue

After Schröters death, the idea of real mountains of Venus fell from popular acceptance. One of the few discussions in the literature about observations of Venus during the early 19th century were the observations in 1841 by Francesco De Vico (1805-1848) (and Palomba) from the Roman College Observatory, who believed they saw a notch along the terminator (Baum, 2001). Later, in 1862 W. Lassell saw an effect that was crater-like on the terminator and in 1873, F. Denning reported a …indentation near the northern cusp. Even the renowned visual Mars observers Schiaparelli, Lowell, Slipher, and Holden all related their own observations of these luminous protrusions. They also vigorously promoted among the general public the real possibility of a mountain range or one solitary peak. Clearly the atmospheric observation of Venus along the terminator was still a problem — and even continues today.

This, combined with a rise in an interest in Venus, prompted popular writers to speculate on the cause of the various phenomena. Some like Webb (1962), for example, continues the theme about the Venusian Mountains. Here he quotes that Schröter had calculated the height of these peaks as;

…supposed to be 27 to 28 miles high [43km.], but of course with great uncertainty. (Schröter, 1792)

Other debates ensued offering other explanations of some causes of the limb projections. Another quote is by Ellen M. Clerke in 1893. (Baum, 2001, p.160) Here she says;

There is, however, another possibility… they may not be solid rock structures but cloud masses piled up to an abnormal height. perhaps at the meeting point of cold and warm air currents. [25]

Venus Terminator Phenomena — Back in Vogue

Schröters phenomena became a popular topic of discussion during the 1880s, only second in some respects, to Lowells infamous canals on Mars. Furthermore, it is also likely that Lowells suggestion that Venus might have similar canals produced on an avalanche of interest in the planet towards the end of the 19th century.

Other observers had already drawn up battle lines against Lowells fantastic canal claims, and they started to scrutinise Schröters claims as well. The English astronomical historian, Arthur Berry (1898) unfairly notes with respect to Schröter: (Berry, 1898, 1961)

…his results are not always reliable. &

Almost the only astronomer of the period whose work deserves a mention besides Herschels, though very inferior to it both in extent and in originally was [Schröter].

After this, some suggested once more that these inequalities were caused by peak(s) rising above the Venusian plains. Three clues held favour;

1) Shape of the cusps and the terminator towards the poles.

2) Shape of the cusp on the southern portion of the planet was more curved that the northern one.

3) The observed, but infrequent appearances of points of light along cusps ends, or within the un-illuminated disk.

Other more positive views about Schröters observational prowess have appeared scattered in the literature. For example. Webb (1962) pg.65, says;

… Schröters observations at the end of the last century are far more trustworthy.

The Debate Continues Into the 20th Century

Henry Norris Russell (1877-1957) said, later in life, that he too had once investigated this question of mountains on Venus in 1898. Although Russell saw the uneven terminator defects himself, he later went on to explained that his and Schröters observations were likely attributed to some unknown atmospheric or deformation effect with the Venusian cusp. Even though Russell may have considered these scenarios were unlikely — Schröters reputation as an observer was sufficient for others to assume his conclusions had some merit. The seemingly regularity of other similar observations of the southern (and northern) disc meant the effect could be a real physical process. If Schröter were correct, Russell concluded, then the height of the mountain summits would have had to be about sixty kilometres!

Similar sporadic reports of southern cusp deviations appear throughout the 20th Century. One of the most interesting is the independent observations by two English amateurs, Frank Sargent and Henry McEwen in 1913. Both observed and documented their observations of a terminator anomaly, which appear like a notch against the planetary limb. This effect sometimes referred as the McEwen-Sargent Feature (Baum, 2001). Reports from other credible amateurs also shows that these effects must have some credence.

It is quite common for modern observers to perceive the northern or southern most parts of the limb as unequally concave or convex, especially around the time of dichotomy. During the gibbous or crescent phases, sometimes parts of the terminator shows familiar short or flat linear segments. Photographic and digital evidence leads to the conclusion that these effects are actually optical illusions resulting from several dark markings in the atmosphere appearing close to the terminator. One favoured explanation is that the terminator is being seen differently by the eye in the eyepiece, such that the observers brain interprets the southern-most portion (the top of the field in the northern hemisphere) as being far more curved than the reverse direction. My own personal series of observations in 1979 show such deformations, except they are at the northern part of the terminator, and possibly showing us the effects of some southern hemisphere bias. About 1981, the current advice to observers was to look at the terminator horizontally across the field of view, instead of vertically, in an attempt to eliminate this bias.

Many observers of Venus are still encouraged to report any phenomena. The primary collection site for observations is the Mercury and Venus Section of the British Astronomical Association in London under the directorship of Richard Baum. (2003)

Mountains — Exposed at Last

In 1962, Goldstein and Zohar of the Jet Propulsion Laboratory retrieved the first radar images of Venus, showing a possible mountain range at latitude –45°S. Goldstein and Zohar reconfirmed this in 1964, and again in 1969. NASAs Magellan spacecraft subsequently showed another prominent peak from the orbital radar images at 10°E, –80°S. This small peak is about six kilometres above the mean height of the surface. Incidental, the tallest large feature is the Australian-sized continent known as the Ishtar Plateau, with the tallest peak being Maxwell Montes, eleven kilometres above sea level at latitude +62°N. Could this feature influence the Venusian atmosphere to produce these visual effects that have been seen so often? [26]


For all the criticisms of Schröters observations, and based on the evidence of the experience and quality of his works, Schröter remains one of the best of all known visual observers. After the destruction of most of his observing notes during the Napoleonic Wars, for us what remains provides an elusive and puzzling mystery. The problem of the Venusian Cusp still remains and therefore warrants some continued observation. In some ways, this is a general guide for all serious visual observers — no matter what we see, always report anything unusual. To quote the active observer, Webb (1963) pg.19;

And, like old Schröter, trust nothing to memory. [His italics]

or as Herschel might have quipped

Draw what you see — not imagine what you see.


  1. Abbot, David (Ed.); The Biographical Dictionary of Scientists: Astronomers (1984)
  2. Baum, Richard, M; The Planets — Some Myths and Realities. Pub. David & Charles pg.48- 83. (1973)
  3. Baum, Richard, M.; The enigmatic Ashen Light of Venus : An Overview., J.BAA., 110, 325 (2000)
  4. Baum, Richard, M.; The McEwen-Sargent feature and the mystery of the Venus contour anomaly.; J.BAA., 111, 3 (2001)
  5. Baum, Richard, M.; Personal communication. (2003)
  6. Berry, Arthur; A History of Astronomy (1898) (Preface: September 1898) & Dover; 2nd Ed. (1961)
  7. Crisp, D. et al.; Near-Infrared Observations of Venus; 20th Annual DDS meeting BAA.S., 20, 14.01, 833 (1998)
  8. Draper, Arthur and Lockwood, Marion The Story of Astronomy. Unwin Bros. p.89. (1940)
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  11. Grosser, Morton;The Discovery of Neptune. Dover (1982)
  12. Herschel, William; Phil.Trans., 83, pg.337, (1790)
  13. Herschel, William; Phil.Trans. 82, pg.201, (1793)
  14. Hoskin, Michael; The Cambridge Illustrated History of Astronomy. pg.188-201, 208. Cambridge Press (1997)
  15. de Le Hire, Phillipe; Mém de l Académie des sciences.; pg.296-97 Paris Obs. August (1700)
  16. Hoyt, William G.; Planets X and Pluto. Pub. Arizona Board of Regents pg.24, 27-28, 30 (1980)
  17. James, Andrew; Neat Southern Planetaries XII, Universe (July) pg.15. (Astronomical Society of New South Wales inc. (ASNSWI) (1998) [See also NSP 12.]
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  20. Panneloek, A.; A History of Astronomy. Dover (1961)
  21. Sandner, Werner; The Planet Mercury. Faber and Faber (1963)
  22. Seiff. A., Kirk, D.B.; In-Situ Measurements of Vertical Winds in the Atmosphere of Venus.; 20th Annual DDS meeting BAA.S., 20, 14.01, 833 (1998)
  23. Simion, W. et al.; Imaging of the Venus Dark Hemisphere at 1.74 μ.; 20th Annual DDS meeting BAA.S., 20, 14.01, 833 (1998)
  24. Schröter, J.H.; Phil. Trans. 85, 120 (1795)
  25. Schröter, J.H. Sur genauern Kenntniss der Mondflèche Vol. 1 Selenotopographische Fragmente from Lilienthal: auf Kosten des Verfassers. (1791)
  26. Sheehan, William; The Planet Mars: A History of Observation and Discovery. Arizona Press (1997) — esp. Ch.3 A Situation Similar to Ours
  27. Webb, Rev. T.W.; Celestial Objects for Common Telescopes Vol 1. Dover (1962)


I would like to thank the following people for their considerable assistance and advise in producing this paper.

Messrs. Richard Baum, Bob Evans, Nick Loveday and Grant Searle


[1] Debated, then denied as real in 1880s by several sources, including Rev. Thomas Webb (1807- 1885) in Celestial Objects for Common Telescopes Vol.1 pg.67. Dover Edition.

[2] Modern writers and Venus observers still debate on what these early observers saw. A summary of the various reasons appears in the literature from time to time. Baum (2001) pg.158, for example, says;

There can be little doubt the early telescopists were deceived, for it is well known that in poor seeing Venus shows features which quite disappear from the sharp images obtained. But if they mistook observational artefact for objective realities it must also be said that some irregularity originates in localised darkenings and brightenings of the terminator shading, resulting in what appears to be depressions or projections in the line of the terminator.

[3] Nor did William Herschel. The first known detailed map of the Moon was produced by Tobias Meyer in 1775. Interesting in the fragments of Schroters remaining is the best reproduction we have of Meyers map. Incidentally, Christian Huygens lunar drawing was published in his manuscript in 1925, several hundred years later.

[4] Observations since by spacecraft of this region have shown it as far more complex. Unfortunately for observers on Earth, we can only see this feature from a low angle, and cannot not peer into its unique depths.

[5] Housing of his family must have been the more important priority. His finances were a problem, as he was dismissed from his Government position. However, King (1979) claims; …he was too old.

[6] Some have also been sympathetic to his fate, which is likely balancing some of other ferocious criticisms levelled personally against Schröter — especially in England. But also sometimes fate takes its hand.

[7] Another example is E.J. Hartung AOST1, whose written observations were completely destroyed during the Ash Wednesday bush fires in 1983. Another, at the time of writing, the destruction by bush fires of Australias Mt. Stromlo Observatory, near Canberra on the 18th-19th January 2003. Here the historic library was also ravished by fire. Although interesting and irreplaceable astronomical work was lost, at least the major astronomical works that were done there continue in the authors papers in libraries throughout the world and on the Internet.

[8] Created by Peter Dolland who supplied the public and the Services demands for telescopes, by constructing telescopes during the Napoleonic Wars. [JBAA., 61, 192ff (1951)]

[9] According to Richard Baum in a personal communication, the change in telescope manufacturer was not due to any problems with Herschel. He says; Not so. The answer is more prosaic. Quite simply and by chance he had found another supplier!

[10] According to Sheeham (1997) the telescope was 19¼-inch (49cm.) f/16 (8.2m).

[11] This telescope bore the plaque with the description; Telescopum Newtonianum XXVII pedum constructum Lilenthal 1793.

[12] Several observers in the 18th Century had noted the relationship between the mean planetary distances before Bode. Even Johannes Kepler (1571-1630) in 1596 Misterium Comographicum had noted the inordinately large gap between Mars and Jupiter, but this was merely commented. The first was the Oxford Professor David Gregory (1659-1708) in his work Astronomae elementa (1702), followed by the German popularist Christian Freiherr von Wolff in 1741. The latters claim was examined by Johann Daniel Titus (1729-96), who was first to notice the planetarygap missing in the orbital relationships. This was first published inComptemplation de la nature in 1766. Here Titus modified Gregorys relationship to produce the relationship; d= [ 4 + 3 × ( 2n ) ] / 10 , where; d = Distance in Astronomical Units and n = Orbit of Number of the Orbital Position of the Planet. In this relationship, the distance value 4+24 does not have any planet corresponding to the orbit. This fact was further extended by the investigations of Johann Elert Bode (1747-1826), who strongly objected to Gregorys nonsense that the missing object might be just a moon of Mars. In 1776, Bode soon became convinced of another planet existing between the orbits of Mars and Jupiter. Later, after Uranus was discovered by Herschel in August 1781, its value equaled almost exactly matched it geometrical sequenced position of4+192, and this also drove further speculations into other possible trans-Uranian planets. These speculations came very popular in both the astronomical community and among the general public. The formation of theCelestial Police was a positive indication of the serious search for minor planetary bodies. von Zack had attempted to predicted a theoretical orbit in 1785 and make some crude searches in 1787 — without success. In 1799, von Zack requested the meeting of some of his prominent German colleagues that lead to the formation of the Society of Celestial police.

[13] Ceres was named after the Sicilian Goddess of harvest and grain, and is alleged to be the virgin represented as the constellation Virgo. Piazzi named it Ceres Ferdinandea, after the goddess and Sicilian monarch and his patron at the time!

[13] Herschel states that Ceres diameter was …at under 100 miles (<161km). Although this was really no better than guesswork, and this value changed very little for many decades. This concluded that Ceres was certainly not planet-sized that was known after about 1803. This was derived not from orbital calculations, but from the apparent magnitude of the minor planet. Ceres present estimated diameter is 930km (1994) and was not really determined or approximated until the 20th Century.

[14] The often given but incorrectly formulator of the famous cosmological question; Why is the sky dark at night? He was a German doctor, and a boyhood friend of Schröter. He was interested mainly in comets and the weather.

[15] During the time of both Schröter and Herschel prominence, Germany was then just a collection of small independent states. In 1814, there were thirty-seven politically independent states all arranged under an agreement with the First Paris Peace Treaty. Historically, the French Revolution, and the subsequent scamble for dominance, rocked the entire European theatre. With the execution for treason of Louis XVI and Marie Antoinette, and the unprovoked attempt of the Prussian invasion of France in September 1792 in trying to isolate Paris from the French revolutionaries, made these times particularly uncertain. Overall the political events throughout most of the European Continent must have layed heavily on Schröters and the populations mind — but also likely in the minds of Herschel and the English people.

[16] Herschel is likely not to have personally favoured the French, as France had declared war on both England and Holland in February 1793. Yet Herschels popularity remained great among the nobility and the Royal Houses throughout Europe — especially after the discovery of Uranus. He visited Paris on invitation in 1801, meeting Pierre Laplace (1749-1827) and even Napoleon Bonaparte.

[17] Such ideas persisted even in the beginning of the 20th Century. The most significant supporter of these claims was the Turkish-born French observer Eugène Michel Antoniadi (1870-1944). As observations of the planet were so difficult, he became the leading expert on the planet Mercury. In 1934, Antoniadi published La Planète Mecure in which he claimed to have seen notable surface features and evidence of a significantly rarefied atmosphere. Such beliefs were held until the time of the Mariner 10 spacecraft, which encountered the planet three times; in March and September 1974 and March 1975.

[18] The first likely description of the ashen light was first seen in 1715 by William Derham, the cannon of Windsor, when Venus was near inferior conjunction. According to Baum (2000), which I have not seen elsewhere, perhaps Giovanni Battista Riccioli in 1643 saw the same phenomena. However, the cryptic and ambiguous statements by Riccioli, leads Baum summary of the observation as; of such an extraordinary character, that is perhaps more correct to credit William Durham.

[19] The true cause, is still being investigated by modern observers and is a regular program of the Mercury and Venus Section of the B.A.A.

[20] Rev. T.W.Webb (1962) pg.65

[21] In hindsight, the rotational period is the usual geocentric view of the world of these times.

[22] Cloud features have been observed in infrared light at 1.74 μ with an average size of 400 kilometres. The present upper atmospheric rotation, like the planet, is retrograde. The upper air around sixty kilometres moves c.100 m.s-1 (Sinion, et al. (1998) and Seiff (1998)) The mean atmospheric rotation encircles the once planet every 4.0 to 4.4 days (Compared to the Earths average of about 12 days.)

[23] However, Herschel could also be the one questioned here, as it has been suggested that his eyesight had suffered permanent damage arising from an occasion when he pointed a small refractor directly towards the Sun.

[24] Herschel, W.; Phil.Trans. LXXXII, (1793)

[25] This is an interesting postulate, but recent evidence has shown by ground-based and spacecraft near-infrared and infrared observations. I.e. Seiff (1998) On Venus the largest measured updraft is some 2.7 m.s-1 at a height of sixty kilometers. The velocity for this to occur is far too small to be an acceptable or plausible explanation.

[26] I speculate — could this southern peak possibly be affecting this atmospheric phenomena?


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