# Bridging the Gap Between Theory and Practice: Astronomical Instruments - Design and Construction of Astronomical Instruments

Author(s):
Toke Knudsen (State University of New York at Oneonta)

### Design and Construction of Astronomical Instruments

I will not go into the the technical details of the astronomical instruments that were designed and constructed the two times that Ancient Mathematical Astronomy ran at SUNY Oneonta. For each instrument described below, there are one or more links to Internet pages with more information, including images of historical specimens. There are furthermore plenty of good sources on the topic of astronomical instruments, including James Evans' book listed above, which has an extensive bibliography. Thus, the following is a general presentation of the instruments that were designed and constructed in Fall 2010 and Fall 2014.

##### Instrument design phase

For the design phase of the course, the students in the class were divided into several groups. In Fall 2010, there were six groups with two students each and one group with three students (the third being the auditor), and in Fall 2014 there were three groups with three students each and one group with two students. Each group decided on an instrument to design. The choice of instrument was made in consultation with me and with feedback from Anderson, who provided information on whether the group's first ideas for designing the instrument were feasible with the equipment available.

The following table shows the choices of instruments and how many groups undertook to design each of them in Fall 2010 and Fall 2014.

 Instrument Fall 2010 Fall 2014 Armillary sphere 2 1 Astrolabe 1 0 Jacob's staff 1 0 Quadrant 0 1 Sextant 1 1 Sundial 2 0 Telescope 0 1 Total 7 4

After the formation of the groups and final decisions on the instruments, each group began to research their instrument. This research culminated in an instrument paper, as described above, after which the group began the actual design process.

Eight class periods of the course were used exclusively for the students to work on their designs. Anderson and I were both available at those times (or an appointment could be made to meet with one or both of us at another time). When meeting with Anderson or me, the students would explain what parts would be involved, provide sketches and dimensions, and justify that the parts would fit together so as to make the instrument functional. Some of the instruments required only a few parts, others more. Anderson and I would discuss the students' ideas and designs, address mistakes, and make suggestions. Students were expected to follow a timeframe that allowed for Anderson to construct a specimen for each group by the last week of the semester for presentation to the other students in the course.

##### Machines and materials used

As has already been mentioned, SUNY Oneonta owns a 3D printer, which serves the School of Natural and Mathematical Sciences (in Fall 2010, before the restructuring of SUNY Oneonta from two large academic divisions to five schools, it served the Division of Science and Social Science) and is operated by the college's Science Technician, Allen Anderson. This was the machine used for most of the parts of the astronomical instruments designed by the students in Fall 2010. However, in contrast to Fall 2010, the 3D printer was not used at all to produce parts for the instruments designed in Fall 2014. This was partly due to the 3D printer not being operational at the beginning of the semester, prompting the students and Anderson to consider alternatives.

The SUNY Oneonta 3D printer operated by Anderson is a Dimension BST-768. The machine prints in a very strong ABS plastic and has an $8''\times 8''\times 12''$ build volume. The models created by the machine are functional and even machinable. The machine requires an STL file to generate a model. At SUNY Oneonta, Anderson uses SolidWorks to generate the required STL file, though there are also scanning devices that can be used to generate the file directly. At this point in time, the Dimension BST-768 is an old machine in terms of material and technology. It was one of the first commercially available 3D printers, and there have been many improvements made since then. The biggest issue with SUNY Oneonta's 3D printer is the resolution of detail, which is limited by the size of the material “stream” that is used to create whatever model is being printed. The resolution of the Dimension BST-768 is on the order of $0.003''.$

In addition to the 3D printer operated by Anderson, the Department of Art at SUNY Oneonta owns a 3D printer as well. The Department of Art's 3D printer is also a Dimension and similar to the one operated by Anderson, though it is a newer model. Recently, in Fall 2014, the Department of Mathematics, Computer Science, and Statistics also acquired a 3D printer. This 3D printer, a MakerGear M2, is a low-end desktop 3D printer. However, the 3D printers of the Department of Art and the Department of Mathematics, Computer Science, and Statistics have not been used for the construction of instruments in Ancient Mathematical Astronomy.

Besides the 3D printer, other tools were used as well to construct parts out of metal, wood, and plastic. For example, the construction of the wooden quadrant in Fall 2014 was done with a handheld electric saw.

##### Notes on the design and construction phases

Overall, no insurmountable obstacles were encountered while designing and constructing instruments. Certain things took longer than anticipated and others were more difficult for the students than expected. In particular, given difficulties and time constraints, we had to change plans for a few instruments, namely, the astrolabe and the telescope. Still, overall we were on track with the timeframe that I had in mind, and in both Fall 2010 and Fall 2014 the students were able to present their instruments to the class at the end of the semester.

Due to a combination of time constraints and cloudy weather at the end of the course in both Fall 2010 and Fall 2014, we unfortunately did not end up doing much in terms of using the instruments practically. Had the time been available, I would have liked to, for example, mark the shadow of the sundials at regular time intervals during the day and to measure the angular distance between two heavenly bodies with the Jacob's staff and the sextant at night. However, it turned out to be too difficult to organize it during the end-of-semester rush.

Toke Knudsen (State University of New York at Oneonta), "Bridging the Gap Between Theory and Practice: Astronomical Instruments - Design and Construction of Astronomical Instruments," Convergence (May 2015)