Experimental archaeology

By Randall Rosenfeld

Transits of Venus are rare events. Part of the excitement in experiencing a transit is the evocation in the mind’s eye of those lucky enough to gather the data to scale the universe, such as Mason & Dixon, Charles Messier, and Captain James Cook, as well as those whose luck was disabled by death, deficient calculation, or despicable cloud, such as Halley, Kepler, and Le Gentil. While watching the transit of 2012 June 5-6 your participation will invite an affinity between the narrative of past transits, and the cutting-edge hunt for transiting exoplanets (à la Kepler mission and beyond), with you as the active and present link. The connection is what you make of it.

It is never folly to broaden the depth of your personal astronomical perspective, or deepen your awareness of the shoulders upon which you stand while looking up, but this mode of seeing can be more purposeful still. Have you ever wondered about how the observations were actually made in 1639, 1761/1769, and 1874/1882? What it was like to view with the optics, measure with the micrometers, register timings with pendulum-regulated clocks, record observations with pen-and-ink, chalk and slate, pencil and notebook, glass plate and photographic lens, train against a mechanical model, and define your style of observing and your systematic errors and those of your instruments? A sense of the sequence of change in the craft of observation and reduction can provide another perspective on what you’ll see in June of 2012. It can do even more than that, however—if done with commitment, intelligence and open eyes it can serve serious research ends.

Get your hands dirty in the experimental archaeology of the Transits of Venus!

Experimental archaeology has long been a part of archaeological science, and is invoked to investigate earlier technologies, techniques, and artifacts. It can be used to elucidate very specific questions, or more general issues. Knowledge about earlier technologies is often incomplete in some essentials, and for some wholly doubtful. Textual descriptions may be lacking, apparently spotty, or seemingly inaccurate, visual evidence may be stylized, confusing, or even incorrect, and the artifacts themselves may be incomplete or apparently unique, offering few clues as to their intended use.

David Rittenhouse, whose account of the 1769 transit was one of the more colourful, used a Gregorian reflector, as did many of his contemporaries. How much do we know about the performance of these optical systems from actually using them? (Image © Specula astronomica minima)

The principles of experimental archaeology are straight-forward enough. As with any experiment, you need to define the question you want to answer, research the relevant sources so that you can formulate a protocol for the experiment, draw up a procurement list of the necessary equipment for running the experiment and recording it, train your research team in appropriate techniques for the trials (the team might just be you—the principal investigator—or it may consist of as many personnel as the experimental protocol dictates and finances allow), analyse the results, and release them.

Principles of best practice of experimental archaeology in astronomical application

1. The equipment used should be that available to the original observers;
2. Techniques should be those of the time, place, and activity under investigation;
3. Modern technicians should not be incompetent, inexperienced, or inexpert in their handling of 1. and 2. above;
4. Modern technicians must be fully informed of the goals of the experiment, and be sympathetic to its aims, unless the experimental design requires them to be uninformed;
5. In regard to 1. and 2. above, modern materials and technologies should play as little a role as possible in the crucial elements of the experiment. Where they are necessary, their use should be controlled, and recorded;
6. Parameters, qualifications, and limits to an experiment should be clearly formulated and stated;
7. Experiments in sequence should be consistent, unless the experimental design dictates otherwise;
8. Experiments should be developed and run with reference to previous trials (if any);
9. All possible ways documented from historical sources that something may have been done should be considered for investigation where practicable;
10. The experiment should be reproducible if at all possible, should the opportunity for similar experiments present themselves;
11. Results must be stated as accurately as possible, with all necessary qualifications, chief among which is that a successful experiment provides only one possible way something may have been done;
12. The experiment should be scrupulously recorded, including any failures of technique, equipment, or observers, using the most appropriate modern technology;
13. The experiment must be published as fully, transparently, and rigorously as possible.

Hands-on familiarity with the astronomical equipment of the past is necessary in order to truly evaluate the quality of old data. (Image © Specula astronomica minima)

Possibilities for archaeological experiment during the upcoming transit

That old data is still of value to astronomy has been amply demonstrated in the work of Prof. Richard F. Stephenson (University of Durham) using historical eclipse data to trace long-term variations in the Earth’s diurnal rotation, or Dr. Elizabeth Griffin’s (DAO) advocacy of the data in historical plate archives to construct long time-bases for crucial astrophysical data, to name a few. If questions arise about how historical data was obtained, particularly in defining how data quality may have been affected by either the technologies or techniques used in its capture, such questions can be usefully pursued through experimental archaeology.
For historical transit observations, there are numerous possibilities:

1) if there are doubts about the published accounts of a particular transit observing team, one could extract their observational protocol (procedures, equipment list, & number and function of experimenters) from their records, and one could attempt to reproduce the results by replicating the means and manner of their observations as closely as possible. If the original reports have omitted anything crucial, rearranged experimental steps, or reported results apparently incommensurate with the equipment and techniques, it would soon be revealed. This would subject a past observational protocol in its entirety to investigation through experimental archaeology.

2) similarly, one may wish to subject a single aspect of a past transit observation to scrutiny through experimental archaeology. This is particularly important with purported ‘discoveries’. Prof. Jay M. Pasachoff (Williams College) has lead important recent work on the limits of historical optical detection of planetary atmospheres. Several 18th- and 19th-century observers and commentators thought they had clearly seen the atmosphere of Venus through relatively uncorrected optical systems of small aperture. An experimental archaeology programme to observe the upcoming transit with equipment and techniques similar to those used for the original observations could help settle the question (it would be most effective if the instruments were doubled to record their performance visually, and electronically).

3) writers on the history of astronomy frequently wonder at the ‘low quality’ of the telescopes used by past observers (such as Charles Messier), and confidently list the deficiencies of such equipment without ever having looked through the actual period instruments, and learned the art of observation as practiced at the time. The transit offers one such opportunity open to those with access to both historic and modern equipment, through the design, running, and recording of side-by-side trials. Many amateur astronomers do similar things with competing varieties of modern equipment, or with equipment of their youth compared to modern technologies.

4) questions have arisen about the preparation and training of observers for past transits. In some historical reports observers remark that their training ill-prepared them for the actual phenomenon of the transit. Purpose-built transit simulators were built for training many of the ‘national’ teams for the 19th-century transits. Some of these exist in usable states, while others could be replicated. Experimental-archaeological trials could be run to assess the effect of these machines in training observers. It may prove useful to employ some of the recording and analyzing equipment used in the present practice of psychology, as well as that discipline’s techniques of analysis in handling the results.

Not all the equipment actually used when observing, planning & reducing observations is mentioned in published accounts or manuscript records. Some effort should be made to discover the 'hidden' equipment, because it too may have affected the quality of data, or at least played a role in the style of observation and data acquisition. (Image © Specula astronomica minima)

5) a different, though not unrelated manner of viewing the transit, is through cognitive archaeology. That is, to try to view the transit as someone would have in 1639, or 1761/1769, or 1874/1882, through the astronomy and cosmology of the day, and through the chronologically relevant visual and literary imagery. It is an extraordinarily difficult exercise to accomplish. The gains would be a very different perspective on the transit—and possibly astronomy in general—which could offer hitherto unsuspected insights into what the past observers were prepared to see, and what they actually saw. One could ready oneself through studying the texts which would have been read in the past, and viewing astronomical illustrations contemporary with the texts, and internalizing both, aiming for a familiarity which would allow one to call up this worldview at will. While it is as impossible to forget what one knows of the present practice of astronomy as it is to time travel and actually see with the eyes of a century or two ago, much may be accomplished in the attempt. It is, in its own way, a sort of thought experiment.

There are many other ways to enrich your personal experience of the upcoming transit by adopting an experimental archaeological approach, and opportunities to do real research through its techniques. As an alternative to research-orientated experimental-archaeological trials—or in conjunction with them—one could incorporate elements of a modified (or ‘relaxed’) experimental archaeology into transit public outreach. If you wish for more information, or advice on designing a programme, please contact: r.rosenfeld@transitofvenus.nl.