AstronomySeventeen years of research on nautical instruments produced various sidelines that were not covered in my PhD thesis. One that fascinated me most was Galileo Galilei's early seventeenth century proposal for longitude finding at sea. Galilei had discovered the first four moons of Jupiter (Io, Europa, Ganymede, and Callisto) in 1610 (see figure 1, for more pictures see the astrophotography page) and soon realised that they formed a heavenly clock that could potentially be used as a reference clock in the determination of longitude by comparing tabulated times of the moments its moons touched the Jovian limb with times from onboard observations.
Although a valid method, the success of it depended on the quality of the instruments and the skills of the observer. In my PhD thesis I have shown that observational skills vary between observers due to difference in human visual perception and that in order to become a qualified observer at least some 500 observations are needed. In addition being on board a moving vessel would not have been beneficial to the results achieved with Galilei's method.
Having researched human perception, using the nautical instruments I created through the years, I wondered what kind of accuracy in longitude finding could be achieved using Galilei's method and especially what the differences between two observers would be. For this I decided to build an observatory on top of our library.
In it the following instruments are currently installed (see figure 4):
Initially only the first two telescopes were installed together with a C11 XLT Carbon (see figure 2), but as the mirror-flop was too large on this instrument it was replaced with the EdgeHD version, which has a mirror-lock to minimise this effect.
The GTT60 was added to the array in September 2018 (see figure 3).
In June 2019 we decided to part with the Celestron C11 XLT and to swap it for a C11 EdgeHD (see figure 4). Reason for that was the fact that the XLT has considerable mirror-flop, which makes it difficult to keep it parallel to the Esprit. Befriended amateur-astronomer Rob Musquetier wanted to sell his C11 EdgeHD as he is only doing astrophotography using APOs and no longer had use for the C11. Our C11 was acquired by the astronomical society AWSV Metius in Alkmaar and will soon be installed in their observatory.
Galilean Type TelescopeIn order to test Galilei's method a Galilean Type telescope was added in September that year. For this I acquired a 60mm objective lens (focal length 1490mm) and a 30x concave ocular (focal length -50mm) from Dr. Roger C. Ceragioli, an optical engineer and professional telescope maker at the Richard F. Caris Mirror Lab, University of Arizona, Tucson (USA). In December he provided additional concave oculars for 20x and 40x magnification. He had made these four lenses for his own research and deliberately made the objective lens of bad figure and polish to mimic the quality that could be achieved in Galilei's time (results of this set can be found at the ATS Forum). As a result the objective lens needs to be stopped down to 30mm aperture in order to get reasonable images.
The OTA I created myself using a motorised Moonlite CS model focuser, an 80x1.5mm aluminium tube, some additional home-made aluminium and bronze parts, and a 2" star diagonal. The scope saw first light at daytime on 28 September 2018 and at night on 3 October that year. Having a 60mm aperture I named the telescope GTT60 (Galilean Type Telescope of 60mm aperture).
Initially mounted in the Lunt rings (see figure 5), the GTT60 was given its final position between the C11 and Esprit in the last week of November 2018 (see figure 3). In order to be able to align it with the other telescopes I created a set of rings that can be adjusted in right ascension and declination (visible as red parts on the mount). These rings are mounted on cross-bars that are fastened to the ADM Losmandy style side-by-side plate.
Next to my own research the observatory is made available to the local schools. In September 2018 eight students, in four groups, of high schools Jac. P. Thijsse College and Bonhoeffercollege have started their research. Topics of their research are:
Sky conditions and astronomical twilightFor the sky conditions and astronomical twilight at InFINNity Deck see the Astrophotography section.
If you have any questions and/or remarks please let me know.
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