The terracing of this formation is the most notable feature. Having a truly magnificent terrace running along the S/E walls, tapering into the northern ramparts; this dominant of all the terracing in the walls, is heavily landslides in several places and also appears to cut right through a small craterlet in the southern wall.
The central massif being lofty in appearance - one peak more so than the other; the northern peak was catching the sun, and was thus very bright and casting prominent shadows towards the east wall.
No other floor detail, other than the central peaks could be discerned.
Several hilly regions are to be seen adjacent and near to the north wall; a double craterlet was easily discerned; and a depression set against the shadow of a long elevation extending away from the N/E wall.
The wall end of the Montes Appenlnes can be seen in the southern terrain, one peak in particular was casting a very long shadow that diminished in intensity towards the end, this is lying due east of the crater. I place the length of the shadow at the same diameter as the crater Eratosthenes itself - 38 miles.
This most noble formation of perfect proportions is always a most splendid sight.
Date. . . . . 20th December 1986
Time. . . . . 00.00 to 01.00h UT
Conditions. . Fair
Instrument. . 6in. Reflector x60 & 120
Observer. . . Vaughan Cooper
Colong from . 134.2 to 134.7
To attempt to draw this feature is not for the faint hearted.
I remember feeling dissatisfied with my drawing till I compared it to a photograph taken at a similar colong, on the 26th Nov 1961 by a Mr WJ Rippengale featured in Practical Amateur Astronomy Ed. by P Moore
Although my drawing is far from perfect, I feel the general outline and proportions of the detail within Janssen stands up fairly well against the photograph so I've decided to publish it as an example to all, not to destroy ones drawings as the final result may not be as bad as you feel about it.
Janssen a vast formation lying in the south east quadrant of the Moon. Over 120 miles across at at its widest point, the interior is very rough and crowded with all kinds of detail, craters, ridges and a huge cleft running from approx the south west wall to Fabricius, seen in my drawing as a thin black sinuous line.
The northern wall of Janssen is broken by Fabricius and in the south by the 30 mile crater Lockyer.
Needless to say the total amount of detail drawn in Janssen is only a tiny fraction of what could be seen.
UNKNOWN WORLDS Part One
By Rob Moseley
(The revised text of a lecture given at the Northamptonshire Natural History Society, April 1972)
In March 1781 the Royal Society in London received a paper from an obscure musician in Bath. It was entitled "Account of a Comet". It ran thus:
"On Tuesday 13th March, beaten 10 and 11 in the evening, while I was examining the small stars in the region of II Geminorum, I perceived one that appeared visibly larger than the rest; being struck with its uncommon magnitude I compared it to II Geminorum the small star in the quartile between Auriga and Gemini, and finding it to be much larger than either of them, suspected it to be a comet. I looked again for the comet, or nebulous star, four nights later and found that it is a comet, for it has changed its place."
The men of the Royal Society little realised that they were reading an account of a discovery unmatched since the invention of the telescope. Six months later the name of William Herschel was on the lips of every men of science. After he was presented with the Copley Medal by the Royal Society its president said, "We see that the treasures of the heavens are inexhaustible. If more unknown planets exist we may look forward to new surprises on the part of science."
The strange object that Herschel's eagle eye had noticed was no mere tailless comet as he had initially assumed. It was an entirely new planet. The effect of this discovery was stunning and produced an intellectual dismay hard for us to appreciate. The five visible planets had been recognised since pre—history. No one had the slightest expectation of any more being found. It was part of the human intellect to view Saturn as the frontier of the Sun's kingdom. It was simply unthinkable that other planets existed. When Kepler supposed that an undiscovered planet lay between the orbits of Mars and Jupiter he was greeted with arguments like this:
"The human head has only seven openings; two eyes, two ears, two nostrils and a mouth, Therefore there can only be seven heavenly bodies."
Even as late as the 19th century, prior to the discovery of Neptune, the philosopher Hegel had proved by logic that there could be no more than seven planets orbiting the Sun.
When Herschel saw his new object then, it is not surprising that the thought of it being a new planet never occurred to him. But it was not a chance discovery. He was carrying out the first of his celebrated "sky sweeps" in which he covered the entire sky in three years. This one he was carrying out with a homemade 6 inch reflector of superb quality; his third and last saw him using the world's largest telescope — his self constructed 48 inch reflector. The discovery of Uranus meant more to science then the addition of one planet, it enabled Herschel to give up music and devote himself completely to astronomy and commence forty years of tireless, brilliant work.
On that historic evening in Bath we may picture Herschel frowning into his telescope wondering what this object shimmering in the field of view could possible be. He substituted an eyepiece of x400 for his sweeping power and then even stepped up the magnification to x932! As he focussed each time the new planet increased in proportion while the background stars remained as sharp points. Beyond a certain power the tiny disc became obscured and badly blurred. It is a tribute to Hershel's telescope that it was almost certainly the only one in existence at the time which would show the minute disc of the planet. Other astronomers were only able to recognise Uranus by its motion. Messier was to write later to Hershel asking how he recognised any peculiarity, as he had watched the planet all night without detecting any movement. When Herschel replied that he had seen a disc the famous French comet hunter could only marvel at the quality of both Herschel's vision and telescope.
A month after Herschel's initial announcement the Astronomer Royal, Nevil Maskelyne, observed the new "comet" from Greenwich and commenced measurements. It was quickly realised that something was wrong. The object was moving much too slowly for a comet, and a rough calculation of its orbit from the limited number of observations to hand indicated that it could never come closer to the Sun than the orbit of Saturn. Indeed Maskelyne actually remarked that he thought the object was behaving more like a planet than a comet, And so it proved to be.
Sir William Herschel (1738–1822)
The discovery that increased the radius of the solar system from 885 million to 1765 million miles certainly brought Herschel to the fore. He had an audience with George III and showed him the heavens through his telescope. The King was no beginner and had already set up his private observatory at Kew. This, and the fact that Herschel was a Hanoverian (though not a deserter from the Army - he was honourably discharged) stood him in good stead. He was granted an income of £250 a year and installed near Windsor as "Royal Astronomer". Herschel was never to become Astronomer Royal, nor did he want to!
Unfortunately, there seemed to be considerable confusion as to how his name was spelt, although we must remember that even at this time considerable latitude in such matters was still common. For a time Maskelyne did not know how to spell his name, and persisted in putting two Rs and Ls. The French, not on the friendliest terms with Britain at this time, were the worst offenders.
In his "Histoire de l'Astronomie" 1785 Bailly speaks of this discovery, Which he attributes to a German Hartchell; he describes the star as a comet, but remarks that "in England they begin to believe that it is a planet." The official French astronomers still called him Horrochelle in the "Connaisance des Temps" of 1784. Pingre, in his "Cometographie" of 1784 classes Uranus as the first comet of 1781 and passes this patronising comment, "This comet or planet, for it is not yet decided if it is one or the other, was discovered in England by M. Herschel, astrophile, they say, rather than astronomer." In fact the riddle of the strange orbit was solved long before 1784. News seemed to travel slowly in France.
Not all French astronomers were suffering from sour grapes though. Bernardin de St. Pierre remarks in his "Harmonies" that "The astronomical editors of that publication" (the Connaisence des Temps) "have intentionally thrown much doubt and obscurity on the discoveries of this great man. The servants who are supported by the State often do very little that is useful; but the worst of it is, they criticise those who work and devote themselves with disinterestedness and zeal to the progress of science."
Herschel wanted to call the new planet "Georgium Sidas" - or George's Star, in the same way that Galileo had courted patronage by naming the four moons of Jupiter "The Medicains". It is commonly believed that Herschel's suggestion was quickly dismissed. This is untrue; the name was contracted to "The Georgian" and used widely in England until about 1850, through understandably, it never came intones on the continent. Others in England wanted to call it Neptune, keep the mythological associations, and give the planet the trident as a symbol of British maritime power. Lalande suggested the name "Herschel". In the end Uranus, father of Saturn and grandfather of Jupiter, was officially adopted after being suggested by Bode.
Although the first man to realise something strange in what he was looking at Herschel was not the first man to gaze on the unknown planet. In fact Uranus had been observed 19 times before its discovery. Flamsteed is acknowledged as being the first man to observe Uranus telescopically, though it was doubtless observed thousands of times from prehistory by men with eyes keen enough to pick it out, because at opposition Uranus is just visible to the naked eye as a dim star of magnitude 5.7.
You will look in vain for the star 34 Tauri on any star map, for this is the number Flamsteed assigned to what he thought was an ordinary star when making his famous catalogue — the "Historia Coelestis". If he had checked more closely the planet could have been discovered on December 23rd 1690, but it was fated to wait 91 years more, and complete more them another revolution around the Sun. Flamsteed actually measured the position of Uranus four times between 1712 and 1715 - recording it as a different star on each occasion. Lemonnier, working in Paris, recorded the planet 8 times during December and January 1768/69. In January he actually plotted its position on four consecutive nights, but due to the haphazard way he made his observations he noticed nothing untoward. Some scrabbled observations were found on a paper bag used for wig power!
It did not take Herschel long to discover two moons of Uranus in 1787, Titania and Oberon. In 1851 Lassell added two more, Ariel and Umbriel. In 1948, using photographic techniques, Kuiper discovered Miranda, a very faint I7th magnitude object.
This is not the place for a detailed appraisal of the physical makeup of Uranus. In January 1986 Voyager 2 flew past the planet giving us for the first time hard information to replace what had previously been informed guesswork. Before Voyager Uranus was, of course, known to be a gas giant belonging to the family of planets typified by Jupiter. It surface temperature was known to be so cold (in the region of —300°F) that only hydrogen, helium and hydrocarbons such as methane would not he frozen solid. Unlike Jupiter hardly any ammonia had been detected. In 1952 Herzberg had indeed detected free hydrogen in the atmospheres of Uranus and Neptune, and he calculated that there would be three times as much helium as hydrogen present. This was recently reduced to 40% of the total volume by some authorities. In fact Voyager has shown that the atmosphere consists of 84% hydrogen, 16% helium and traces of methane and acetylene.
Part Two of this article will be continued in MIRA 18. VC