The primary instrument I’ve used for my observing is an astronomical quadrant. That instrument is designed primarily to measure the angular distance of an object above the horizon1, otherwise known as its altitude. However, this isn’t the only instrument good for this sort of thing. Brahe’s Astronomiae Instauratae Mechanica is filled with instruments that essentially fill this same purpose, but in different ways.
One design, he describes as a “parallactic instrument” but it was also known as a triquetrum in period. This design dates back to Ptolemy and is described in Chapter $12$. Here’s a drawing of it from Toomer:
Continue reading “Almagest Book V: The Parallactic Instrument”