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Grateful thanks to all those that have provided many of the articles, references and details in these pages
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Observations at the telescope
Soon after the telescope was effectively completed, Craig was keen to begin observing evenings to test the instrument's capabilities. He invited many prominent astronomers to visit his telescope, including William Parsons, builder of then the world's largest reflector - having a mirror six feet in diameter.
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Confirmation of Saturn's "third" ring obtained at the Craig Telescope This engraving represents the only record of any work undertaken at Wandsworth. It was produced by a Fellow of the Royal Society from records made at the eyepiece during Saturn's opposition around 20 November 1853.
Courtesy of The Illustrated London News. |
We get a sense of the wonder that this huge refractor at Wandsworth brought to both the scientific and local community in an abstract from the Illustrated London News dated 28th August 1852, "The powers of this telescope, as a measuring instrument, are unapproachable by all others. It separates minute points of light so distinctly that its space penetrating qualifications will render it, as a discovering instrument, one of a most superior order. It resolves the Milky Way, not simply into beautiful and brilliant "star dust", to use the language of astronomers, but actually subdivides it into regular constellations. We thus, in what at least was heretofore separated into minute points of light, can now behold counterparts of our own Orion and Cassiopeia, our Greater and Lesser Bear; and, also, evidently adorned with the most generous colours."
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| Saturn lying in Taurus in early December 1854 would have been well placed to make excellent observations of its disk and rings. However, it may be that its inclination was too high and that maneovering the Craig Telescope into position proved too much of a challenge. |
We can imagine what the summer sky would have looked like in 1852 during the early hours of a warm autumn morning on the Wandsworth Common. The huge constellation of Cetus the whale would have stretched across the southern sky with Taurus the bull swinging high up over the south eastern horizon. The vista would have been punctuated with a myriad of stars. With only the small-town lights of Wimbledon glowing very faintly on the southern skyline - the heavens would have been a magnificent sight. Added to this, Saturn shinning brightly, with its pale hues, towards the south east in Taurus.
Perhaps Craig had been inspired by the Great Exhibition in London in 1851. Maybe he had made a special visit to see what mysteries lay inside the Crystal Palace at Hyde Park. There were many scientific inventions and equipment, including displays of telescopes and early daguerreotype and calotype astronomical "photographs". Those of the Moon captured by William Cranch Bond from the United States, had won a medal.
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Or, perhaps Craig was bitten by the "discovery bug" that was now taking hold in every corner of scientific endeavour, especially astronomy.
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A representation of Saturn's likeness as seen at the time the engraving to the left was made. The fact the Encke Gap in the A ring is absent may indicate the problems encountered with the slightly undercorrected optics of the telescope.
At the beginning of December 1854, Saturn was at opposition and would have been better placed to reveal its faint third ring. Still in Taurus and high in the sky, it would have been a magnificent sight. |
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This image of the crater Clavius is one obtained by Paul Hermonat in the United States using a 6-inch refractor made by Thomas Slater at his London workshop.
Courtesy of Paul Hermonat. |
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On 17 July 1850, Bond working with photographer John Adams Whipple, focused the light of Vega onto a highly polished, iodine fumed silver plate to produce the first ever photograph of a star.
In the heady days during photography's infancy, astronomical breakthroughs occurred regularly. The first successful daguerreotype of the moon was captured in 1840 followed by that of a solar eclipse in 1842. An image of the solar disk a mere three years later in 1845.
Unlike Craig, Bond and Whipple were not relying on photographic equipment alone, they were also using the Harvard College Observatory's new 15-inch refractor. It was and still is today a magnificent instrument.
The observatory's ongoing interest in the application of photography to astronomy distinguished this telescope's early contributions. After the addition of a new clock drive to the telescope, George Bond embarked on an ambitious programme of photography based astrometry measuring the positions, parallaxes, and proper motions of celestial bodies.
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William Cranch Bond and his son were the first to observe the then innermost ring of Saturn, termed the Crepe ring when they pointed Harvard’s telescope towards Saturn in 1850. It was this illusive ring that Craig had wanted to confirm.
At left is a drawing of Saturn made on 10 September 1851 by William Lassell with his 20 foot telescope.
Copyright © of the Royal Astronomical Society
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| On a visit to the Craig Telescope Rev. T W Webb would have seen a beautiful sky on the evening of 28th October 1852 at 11pm. The planet Saturn would have been an easy target although the proximity of the full Moon may have hampered any attempt at seeing the Crepe ring of Saturn. |
With Saturn high in the sky on the evening of 28th October 1852 it would have been very close to the almost full Moon. The inclination, some 43° up, would have made it quite difficult to observe from within the dolly. Although, around midnight, the only motion needed to follow the planet would have been in azimuth as the planet crossed the meridian.
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The Hunt for the Crepe Ring
It was around this time that Craig seemed to realise some kind of quest - a quest to join in at the forefront of astronomical discovery. It seems he had built into his plans for the telescope a programme of observation, a reason to build it in the first place - to observe both Venus and Saturn. That was it. He believed, using his new telescope, he could confirm the existence of the Crepe Ring discovered inside the main ring system of Saturn at the Harvard Observatory. Although the ring had been observed on several occasions many years earlier by a number of prominent astronomers, none had realised what it was they were seeing.
So the hunt for Saturn's third ring was on. We get a feeling of that fateful night from an extract in the Leamington Courier, 2 November 1906, it reads, "The instant result has been to set the question at rest for ever amongst astronomers as to the satellite having a third ring. The Craig telescope at Wandsworth has brought out this third ring beautifully. It is of a bright slate colour, and one of the Fellows of the Royal Society is preparing a regular drawing, made to scale, of the planet Saturn, exhibiting it with its rings, as now palpably defined through the noble telescope. We are unable to state the powers brought to bear upon the planet when the rings were discovered. We believe, however, as the night itself was only of a moderate kind for astronomical observations, powers of about 500 merely were used."
Interestingly, the article goes on to state, "The appearance of the moon in crossing the meridian at midnight - this telescope having a power of about 1,000 looking upon it - is an object of surpassing beauty." The full Moon passed due south at mightnight slightly to the right of Saturn on 16 November 1853, some four days earlier than suggested in this text. By the 20 November it was transiting the meridian at 03:15UT and was only 84% illuminated. We might surmise from this that there were a number of nights over which this task of recording Saturn's third ring took place.
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It is clear from an extract in the Illustrated London News 16 October 1852 that once proclaimed other astronomers wanted to make sure, "When news of this reached England, the Northumberland achromatic, at our Cambridge University, was brought to bear, by Professor Challis, on the rings of Saturn, and he failed in discovering the third: so, also, with the giant reflector of the Earl of Rosse. Hence it became a matter of intense interest, as to whether there was in reality a third ring. We are happy now to exhibit an Engraving of the Ring, as seen in this country. In the Craig Telescope - engraved and described in the Illustrated London News for August 28 - this third ring is quite palpable; so that there can be no longer any doubt as to its existence. The colour of this ring is a brilliant slate. The great quantity of light which the telescope at Wandsworth brings to the eye of the observer from this planet gives, we presume. this bright appearance to what in instruments of less power is in fact completely invisible."
This rush to check the observations may have been in response to some disbelief - a sense of lost opportunity for the larger and more successful observatories.
George Airey, the Astronomer Royal, was not a man to waste the valuable time of the excellent instruments at Greenwich on such trite exercises.
The Moons of Venus
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Jacques Leibax Montaigne (1716 - 1785) recorded the apparent motion of Venus' moon over period of days in 1761. This is obviously a montage of several observations since the moon shows a different phase angle to the parent planet depending on its supposed orbital position - in reality the phase angle of both Venus and its moon would be the same.
Could this actually have been more to do with optical aberrations within Montagne's telescope? |
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It was also a wish of Craig to finally answer the question as to whether Venus possessed any moons. The debate had been around for some time and it was hoped that the new telescope would be able to resolve this issue.
Venus' orbit lies inside that of the Earth. Through a telescope it exhibits phases just like our Moon - with some of its surface not illuminated by the light of the Sun. If it possessed a moon or moons then they too would also exhibit phases.
There are essentially two ways in which to discover a moon for Venus. Firstly, to observe it directly. This is a little tricky as Venus always stays close to the Sun in the sky; so it is seen in the evening sky soon after sunset at "eastern elongation" or the morning sky just before dawn at "western elongation". Great care would have to be exercised. Potentially, it could mean accidentally looking directly at the Sun leading to immediate blindness!
Secondly, wait for a Venusian transit of the Sun. Using a special solar filter or solar image projection, it would be possible to see any little moons as very small black spots accompanying Venus' silhouette, as they pass over the Sun's disk. However, these transits are extremely rare occurring every 120 years! Some consolation may be gained by the knowledge that most, but not all, happen in pairs spaced some eight years apart. When Craig built his telescope in 1852, it would be a mere twenty four years before the next one to occur in 1876. Unfortunately, by then the telescope had long since been demolished.
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To discover a moon would resolve Venus' mass and density; giving scientist a better understanding of Venus as a planet.
The first to notice Venus as possessing a moon was in 1672, by Giovanni Domenico Cassini, one of the prominent astronomers of the time, who noticed a small companion close to Venus. He decided not to announce his observation, but on seeing it again 14 years later, he entered the observation in his journal. The object was estimated to have about one-quarter the diameter of Venus, and it showed the same phase as Venus.
However, in later years the "moon" of Venus was seen again by James Short in 1740, Andreas Mayer in 1759, and Joseph Louis Lagrange in 1761. In fact during 1761, the object was seen a total of 18 times by five observers. The illustration by Montaigne which he sketched also in 1761 shows what appears to be a moon of Venus at various positions in its orbit around Venus over period of several days. Certainly, from this drawing, it shows that if indeed there was a moon it appeared the same size as our moon but orbiting considerably closer! It also had an orbital period of about fifteen days! If these facts had proved to be correct, Venus would have had a density only one third that of water!
The observations of Scheuten on June 6, 1761 was especially interesting. He saw Venus in transit across the Sun's disk, accompanied by a smaller dark spot on one side that followed Venus in its transit. However, Samuel Dunn at Chelsea in London, England, who also watched that transit, did not see the additional spot.
In the intervening years more sporadic reports of Venus having a small companion seemed to pervade the scientific community. Various hypothesis were contrived to explain this elusive object.
Even the great William Herschel made an earnest attempt at witnessing this moon but failed.
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In early October Venus was at maximum western elongation. Any observations would have necessitated an early morning session. We know that the telescope had no accurate means of calibration with reference to the sky, so finding objects would have required locating them by eye first, then finding them in the finderscope, before employing the mighty 24-inch lens to the task. Therefore, Venus had to be located first. This was much easier during dawn as Venus appeared as a very bright star against the starry backdrop. There was also no danger of accidentally peering at the Sun. The October apparition was very favourable indeed for Craig and his fellow astronomers. Rising just south of east, Venus would have been spotted immediately climbing above the perimeter fence right on time. Since it was moving in both inclination and azimuth, tracking the tiny disk would have require a great deal of patience and aptitude. The view, however, of its tiny crescent would have been breathtaking - albeit fleeting unless tracking was maintained. No records of any observations of Venus exist. The only conclusion, therefore, is that the task proved exceedingly difficult, and not whether Venus did or did not possess any satellites. The attempts must surely have been recorded, for any observations proving or disproving the case would have been written up.
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Snapping the heavens
There are references to photographs being acquired through the telescope.
However, since the instrument was in no way driven, it was unable to track any celestial object with any degree of accuracy. This would have limited its photographic capability greatly.
Early photographic emulsions were very insensitive, requiring many minutes to pick out relatively bright celestial objects. So following the target object would have been essential. The only objects where exposures were short enough to have foregone a drive would have been the Moon and the Sun.
The Moon was well placed in the first month of operation of Craig's telescope. Although slightly below the ecliptic the three-quarter Moon would have set around 11:00pm on 21 September 1852. Most of the main surface features would have been visible and it would have offered a good opportunity with the telescope to capture some excellent photographic images. Because the job of aligning the instrument seemed fairly taskful and the dolly quite confined, having the moon low down may have aided the astronomers to operate all the photographic equipment more easily.
As has already been outlined, moving the telescope in azimuth only, would have involved far fewer errors in tracking. The Moon would have crossed the ecliptic close to the winter solstice and been more or less due south on the evening of Christmas Day 1852. Whilst this would have been most favourable, Rev. Craig would surely have been sensitive to this particular festival and would have lamentably foregone such an ideal situation.
The next opportunity, although not quite as ideal, was the very next month on 22 January 1853. The 12 day old Moon would have afforded a virtually full aspect with 95% of its surface illuminated. The downside was the dolly's position and angle of the telescope's tube. With the Moon some 60° above the horizon, the astronomers may have struggled a little to centre the image on the calotype photographic negative.
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We find our only reference to an observation made in 1854, two years after the telescope was completed, in a paper by Rev J B Reade who worked with the telescope to photograph both the Moon and the Sun. Observational reports are rare - there are no notebooks hidden away in a library somewhere containing the detailed machinations of astronomers, their minds recording every thought as they pondered the heavens.
However from Reade's entry we get a vague sense of both the tentative achievements and the frustrated efforts of the few that did attempt study with the Craig Telescope.
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This facsimile represents the image of the Moon attained at the focus of the Craig Telescope on the evening of Wednesday, 6 September 1854 and shown to the British Association for the advancement of Science later that very month.
It takes into account the phase and libration aspects of the Moon at that time.
All the features mentioned in the report of the image can be seen including the craters Kepler, Menelaus and Plato. True to the description it shows that the bright area around Tycho is overexposed and that despite careful manual attempts to keep the Moon's image exactly centred in the frame during the 35 second exposure, tracking errors have become all too apparent. |
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It reads, "The more important drawing is a large positive picture of the full moon, nearly nine inches in diameter, and therefore on a scale 250 miles to the inch, of which the negative was taken, on the 6th of September, in the focus of the ‘Craig telescope,' at Wandsworth, whose diameter is 24 inches and focal length 77 feet, - and when I state that it is the first attempt, it will be received, notwithstanding certain imperfections of manipulation, which are not concealed by artificial tinting, as a step in the right direction. All the more important features of the moon's surface will be discovered by those familiar with their telescopic appearance, and the portion of the eastern hemisphere admits of interesting comparison with the sun's daguerreotype copy already described. We find in both, and with almost equal distinctness, the Mare Foecunditatis and Mare Tranquillitatis to the south and west, - the Crater Manelaus with ray already spoken of, - the semicircular ridge round the Mare Imbrium, and the unreflective crater, Plato, at its north-west extremity. On the western side, we have the bright Aristarchus, Kepler, Copernicus, and Tycho, with the streams of molten lava extending over the southern hemisphere; but owing to the phase of full moon, the craters and mountains are not relieved by shadows. The time of exposure of the collodion negative was thirty-five seconds; but it is evident that Tycho and the brighter portions are overworked. In the absence also of an equatorial mounting, perfect steadiness could not in the first instance be secured. Mr Gravatt applied a micrometer screw to the eye end of the telescope, and turned it with a winch handle, and when the moon was on the meridian this was almost tantamount to an equatorial motion for the space of thirty-five seconds. A fine wire stretched across an aperture in a slip of wood was placed close behind a negative when in the focus of the telescope, and Mr Gravatt found that by humming a tune he could turn the handle of the micrometer so steadily as to keep Aristarchus continually bisected. Mr Prout, who prepared the collodion surface, unfortunately counted the seconds too loudly for ‘the man at the wheel,' and hence arose a little cause of unsteadiness, which was afterwards prevented by my attending to the time of exposure instead of Mr Prout. Collodion pictures of the moon, as well defined as her image on the ground glass, and taken through all her phases, would leave scarcely anything to be desired in consequence of the the magnifying power of the object-glass itself; and future experiments will be directed by Mr Craig into this channel.
"On the night of the 11th of September, we renewed our attempt when the moon was in a more picturesque position; but an undetected source of error, and the increasing density of the fog when the moon was on the meridian, prevented us from procuring a successful negative. Moreover, the true photogenic focus has not yet been obtained by means of sulphate quinine. I may state, however, that the division in Saturn's ring, the slate-coloured ring, and the inner satellites, were well brought out with my solid eye-piece, under a power of 300; and α and ε Lyrae, with their minute companions, were also well exhibited. In fact, the present superiority of the telescope, though confessedly admitting of improvement in figure, consists in its command over the faintest points of light. That so large an object-glass worked at a mechanical disadvantage by hand, and not machine polished, should do so much in its first offer to the stars, is far from discreditable to those who calculated and ground the curves; and the errors, which are now known and estimated, will be corrected by reworking the surfaces on the plan adopted by Lord Rosse and Mr. Lassell."
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The image of the Moon was secured sometime around 9:45pm on the evening of Wednesday, 6 September 1854, one year after the telescope went into operation. The Moon was more or less due south in Aquarius, moving only in right ascension from left to right and some 20° above the horizon allowing the astronomers to keep the telescope tube at a reasonable angle so that access to the eyepiece end was maintained. No doubt, these early attempts at astronomical photography were focused on map making since it was the full Moon that was being sought. Capturing the relief in the craters and mountains on the lunar surface would have to wait until this exercise had been perfected.
The extract is extremely revealing. We get the distinct impression that all is not well with the setup. It has taken quite some time to even get to this state of affairs and all there is to show for it after much efforts is a rather poor photographic image.
Reade explains that the telescope is difficult to use and even refers directly to the absence of a drive - something that is so fundamental for any instrument especially one attempting to break new ground. Without a drive, centering and keeping aligned a target object would prove impossible.
Imaging the Solar disk
There are a few brief references to the astronomers attempting unsuccessfully to capture images of the Sun's disk. Mentioned in the same report, "On the 12th, the morning following, I endeavoured, with Mr Gravatt, to take the sun on the meridian, and on the same scale as the moon; and I succeeded by an instantaneous operation in exhibiting, in the negative, the peculiar mottled character of the surface which is usually brought out by high magnifying power. Dr Diamond, who printed the positive of the moon, found the sun picture, however, rather overdone for transferring, - It will be necessary, therefore, either to use collodion and nitrate of silver simply, without any or but little sensitive solution, or else to pass the sun's rays through some coloured glass, which will partially retard their energy. A series of pictures of the spots on the sun, as well as of the general surface, may then be successfully obtained; and hence it is not too much to anticipate some accession to our knowledge of the physical character of both our great luminaries by means of this gigantic telescope, which Dr. Diamond enables me to exhibit photographically to the Section."
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Attempting to photograph the Sun would have been very dangerous and difficult. The one saving grace is that the photographic exposures woud have been extremely short. |
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The operator used a very short exposure an "instantaneous operation", but sadly this image seems not to have been printed because it was considered overexposed. There is talk, however, of using "coloured glass" to filter the Sun's image, weakening its bright light to improve the exposure.
After discussing a daguerreotype of the moon taken by Bond in USA, and two calotypes by Henry Pollock, Rev J B Reade reports how a group of Astronomers, including himself used collodion negatives at the Craig Telescope. They were prepared by Prout and printed by Dr Hugh Diamond.
Sadly, these photographs evade discovery - presumably they were not considered good enough to keep and secure for the future.
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Mars proved too much
 When the telescope experienced first-light in the autumn of 1852, Mars would have been a very difficult object to observe. Low down in the east, it would have taken observers at Wandsworth time to locate its puny stella image against the bright autumnal evening sky shortly after sunset. At magnitude 1.7, its 4-arc second disk would have revealed little of its surface details. So the astronomers would have had to have waited until end of February 1854 to see Mars again at its best. Even then it was not such a favourable apparition revealing a disk only 13.9-arc seconds in diameter - compared to a possible maximum apparent diameter in excess of 25-arc seconds! But by this time enthusiasm for using Craig's monster ‘scope had already shown signs of waning, so waiting for a more advantageous apparition looked bleak.
An opportunity to discover the two diminutive moons of Mars, Phobos and Deimos was lost. They were eventually found in 1877 by Asaph Hall using the 26-inch Clark refractor in Washington, the largest refracting telescope in the world at that time.
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