Astronomy

My first picture of Jupiter and Galilean moons Ganymede, Europe and Io (moons enhanced).
Figure 1: My first picture of Jupiter and Galilean moons Ganymede, Europe and Io (moons enhanced).
Seventeen 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.

The set-up at InFINNity Deck when it opened (left to right: 150mm APO, C11, Lunt).
Figure 2: The set-up at InFINNity Deck when it opened (left to right: 150mm APO, C11, Lunt).
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 were installed in May 2018:
  • Sky-Watcher Esprit 150 ED Super APO refractor;
  • Celestron C11 Carbon reflector;
  • Lunt LS80THA solar refractor.
The three telescopes are carried by a 10 Micron GM3000 HPS mount which is sufficiently large to take this load.



The GTT60 (upper left) temporarily mounted on the C11 in the rings for the Lunt.
Figure 3: The GTT60 (upper left) temporarily mounted on the C11 in the rings for the Lunt.
In 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 Roger Charles Ceragioli, an experience lens maker from Tucson, Arizona (USA). He had made these 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).



One of the high school students measuring the GTT60's TFOV using Vega (Alpha Lyrae).
Figure 4: One of the high school students measuring the GTT60's TFOV using Vega (Alpha Lyrae).
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:
  • Determining the orbital period of Jupiter's moon Io;
  • Determining the distance Sun - Venus and Sun - Pluto;
  • How to make colour images using a monochrome camera;
  • Determining the true and apparent field of view of the Galilean-Type Telescope.
Of course the observatory is also used for visual observing and for astrophotography.

If you have any questions and/or remarks please let me know.

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