Bridging the Gap Between Theory and Practice: Astronomical Instruments - A Quadrant

A Quadrant

A quadrant is an instrument used to measure the angle between a heavenly body and the horizon; that is, the altitude of a heavenly body. The instrument is a quarter of a circle with the circumference portion divided into 90 degrees.

For more information about the quadrant, Epact, an electronic catalogue of medieval and renaissance scientific instruments from four European museums, has an article dedicated to the quadrant at http://www.mhs.ox.ac.uk/epact/article.php?ArticleID=14. In addition, the Starry Messenger Project, developed by the Whipple Museum of the History of Science and the Department of History and Philosophy of Science at Cambridge University, has a website dedicated to the quadrant and the sextant at http://www.hps.cam.ac.uk/starry/quadrant.html.

One group in Fall 2014 decided to construct a quadrant. The group's quadrant was made of wood, and, with a radius of \(47.75'',\) it is a large instrument. The group made the decision to make a large instrument because its accuracy would be significantly greater than that of a small, handheld quadrant. In other words, the larger the quadrant, the more accurately one can determine the altitude of the celestial body in question.

The quadrant was designed and constructed entirely by the students, who used the workshop belonging to one of them for the construction part.

Figure 4. Student plans for a quadrant from Fall 2014 Ancient Mathematical Astronomy class

Figure 4 shows the group's sketch of a quadrant. The design of the instrument followed this original sketch.

Figure 5. Completed quadrant from Fall 2014 Ancient Mathematical Astronomy class (photograph by Toke Knudsen)

The above is a photo of the finished quadrant. It is not entirely clear from the photo, but the top edge of the quadrant has three sights lined up properly. The small white bottle seen at lower left is suspended from the top-left corner of the instrument and serves as a plumb. The circular edge of the instrument has the degrees from 0 to 90 marked on it.

Figure 6. Students demonstrate the use of their quadrant in Fall 2014 Ancient Mathematical Astronomy class (photograph by Toke Knudsen)

The quadrant can be used practically, as seen in the above photo of the members of the group demonstrating how to use the instrument to the rest of the class. The small white bottle is seen hanging from the quadrant at the right side of the leftmost table, marking an angle on the instrument. The quadrant's accuracy, however, was not great since the marks for the degrees were not marked accurately enough.