Wayward Comet:. Martin Beech

C/1718 B1 --- 1.00 148.84

Table 1.3. Details of the comets studied by Nicolaas Struyck. Column 1 is the letter labeled as used in his illustration (our figure 1.21). Column 2 is the year of the comet as given by Struyck, while column 3 provides the present-day cometary identification. Columns 4, 5 and 6 indicate the orbital period (technically infinite if the orbit is parabolic: e = 1.00), the eccentricity and orbital inclination. Notes: (1) Often identified as Chéseaux’s comet, this comet ranks as one of the greatest in all of history. It was remarkable for being both very bright and for showing multiple tails. (2) The linkage between comet C/1678 R1 and periodic comet 6P/d’Arrest was made by Carusi et al., in 1991. In his 1753 study Struyck deduced a parabolic orbit. Heinrich Louis d’Arrest discovered his comet in June of 1951, indicating a remarkable 41 returns to perihelion since the 1678 sighting. (3) This is the parent comet to the October Leonis Minorid meteor shower.

      With Struyck we see the first 3-dimensional, albeit on a 2-dimensional page, rendition of cometary orbits. And accordingly the Solar system takes-on a more dynamical feel: the sedate and circular motions of the planets being enveloped in a Gordian knot of cometary paths. The image also hints at the distinct possibility that collisions might occasionally occur between planets and comets – this being more apparent, in some strange optical sense, than in the case of the standard 2-dimensional diagrams (e.g., figure 1.19), where the orbits must, of necessity, cut across each other. It is as if by adding the third dimension, the real threat of cometary collisions is lifted, literally, right from the page – it is the real solar system that is now being portrayed, raw and primordial. No longer the neatly drawn and ordered orbital diagram of the earlier philosophers, the 3-dimensional cometarium of Struyck reveals the inner solar system to be dynamic and perhaps, alarmingly, somewhat overcrowded. Isaac Newton had already hinted at the possibility of collisions between comets and planets in his Opticks (1704), and William Whiston (recall figure 1.19) had additionally suggested that a comet passing close by the Earth might have precipitated the biblical deluge. Furthermore, Whiston argued that comets, “seem fit to cause vast mutations in the planets, particularly in bringing on them Deluge and Conflagration…. [they are] instruments of Devine vengeance upon the wicked inhabitants of any of these worlds” (here Whiston is invoking the commonly held idea at that time that all of the planets in the solar system were inhabited). Indeed, Newton writes, “whence is it that Nature doth nothing in vain; and whence arises all that Order and Beauty which we see in the World? To what end are comets, and whence is it that Planets move all one and the same way in orbs concentrick, while Comets move all manner of ways in Orbs very eccentrick”. The general idea that comets might on occasion collide with a planet, and specifically Earth, however, was not a strongly supported idea during either the 18th or 19th centuries. Indeed, a form of group denial, in effect, set-in during these centuries, with philosophers choosing to believe that the solar system was so well ordered and so well constructed that collisions were either impossible, negligibly rare, or, if they occurred at all, were for very specific God-ordained purposes. And indeed, as a mirror to the heavens, so it was on Earth too – the idea of slow, gradual change, rather than catastrophic punctuations, was dominant amongst natural philosophers and the proof of concept was provided for by Charles Lyell in his highly influential, multi-volume, Principles of Geology (published between 1830 and 1833).

      Not all predictions concerning comets come true, and such was the situation with the (non)comet of 1789. Highlighted as one of Edmund Halley’s originals, it had been reasoned that the comets sighted in 1532 and 1661 were one and the same, and with an apparent period of some 129 years its return some time circa 1789 was expected. Indeed, Bartholomew Burges in his work, A short account of the solar system and comets in general: together with a particular account of the comet that will appear in 1789 (published in 1789), reasoned that, “we may reasonably expect the comet in question, to be visible towards the latter end of 1788 or the beginning of the year 1789, and certainly some time before the 27th of April 1789”. For all of the great confidence that Burges invested in his prediction, no comet appeared. In spite of pinning his hopes upon the wrong cometary return, Burges’s text remains interesting because of two attached fold-out charts. The first chart (figure 1.22) shows to scale the predicted path for the comet of 1789 as it moves interior to the orbit of Uranus and in towards the inner solar system. While the first chart is not specifically innovative in its construction (other than showing Uranus as the new outermost planet), the second chart is altogether something different. Burges writes, “I have annexed to this work, a diagram, to which I have fixed threads, which when extended shows the perihelion distance of the comet – show the angle its orbit makes with the ecliptic, and the distance the Earth will be from it at that time – to be measured from the scale of the diagram”. Here we have a three-dimensional, predictive, scale model for the comet. While not the first pop-up book to be manufactured, the text by Burges may well be the first that was specifically produced to reveal the true spatial and temporal motion of a comet – albeit a comet that didn’t actually appear. The path of the comet, above and below the ecliptic plane, has been drawn on a semi-circular piece of paper that folds-up above and below the base page representing the ecliptic. The Earth’s orbit is drawn to scale along with date and position markers, and the attached threads can be set and used to determine the Earth and heliocentric distances to the comet on specific dates. For the price of the pamphlet, one could literally hold the orbit of the comet in the palm of ones hand.

      Figure 1.22. Foldout map of the solar system by Bartholomew Burges (1789). The orbits are shown out to “planet Herschel” (Uranus), which was first identified by William Herschel in March of 1781. Along the cometary path can be read the following, “The path of the comet that appeared in the year 1532 and 1661 with period 128 yrs. 89 dys. 24 m. & will consequently be visible again on or before the 27 of April 1789”.

      In addition to producing his pamphlet on the solar system and hyping the supposed appearance of the comet in 1789, Burges also set out to deliver a series of lectures on the topic in the Boston area. An advertisement [7] in the Boston Gazette for 16 February, 1789 indicates that these lectures will feature a display of astronomical apparatus. Indeed, we are told that the display constitutes, “two large Planispheres and Gilded Projectiles, displaying the Celestial Bodies, suspending in their due Proportion, and their orbits; and their relative and mean Distances from the Sun, with their moons and Satellites”. The exact layout of the system is not clear from the advertisement, but it would appear to be some kind of ceiling-mounted planetarium display that was being shown (figure 1.23