Nicolaus Copernicus' observational instruments
Solar quadrant
Observations of the Sun’s position on the celestial sphere were among the most important observations made by Nicolaus Copernicus. He used for this purpose one of the astronomical instruments from his observatory (pavimentum).
The solar quadrant was a square-shaped wooden plate. An angular scale from 0 to 90° with an accuracy of 1° was plotted on the precisely aligned surface of the plate. It represented a quarter of a circle. The quadrant placed on the well-leveled surface of the pavimentum in the plane of the local meridian, that is, perpendicular to the horizon, made it possible to determine the altitude of the sun above the horizon. It was used for this purpose by Nicolaus Copernicus during his observations in Frombork.
The altitude of the Sun could be measured by observing the shadow cast by a gnomon fixed on a plate in the center of the circle and perpendicular to its surface, reading from the scale the angle determined by the center of the shadow. Using the quadrant, Nicolaus Copernicus determined the angle of inclination of the celestial equator to the ecliptic (the path of the Sun in the sky).
By making observations of the Sun using the quadrant, Copernicus was able to determine the extreme values of the Sun’s altitude at the observation site during the winter and summer solstices. This allowed him to confirm the value of the inclination of the Earth’s axis of rotation to the orbital plane, known since antiquity. Thanks to these observations he could also determine the latitude of Frombork, which was very important for Nicolaus Copernicus when observing the stars and planets in the night sky over the Vistula Lagoon.
The astronomer made his most important observations in the Frombork observatory in 1515 and 1516. Most likely, he made the first ones already in 1512 or 1513.
In the autumn of 1516 Copernicus leaves for Olsztyn, where he assumes the duties of administrator of the estates of the Warmian chapter. There he creates his famous solar chart on the walls of the castle’s cloister. Earlier observations made with the solar quadrant in Frombork were probably extremely helpful in plotting this table.
The parallactic triangle (triquetrum)
Nicolaus Copernicus had several observational instruments in his observatory. He constructed them from wooden elements, using the descriptions of the ancient masters.
The name of the instrument itself originated in the Middle Ages, but directly referred to the astronomical instrument constructed in antiquity, which was first described by Claudius Ptolemy in his most famous work Almagest.
The parallactic triangle (triquetrum) is an instrument composed of wooden slats joined together in such a way as to form an isosceles triangle. One of the arms is attached to a wooden post with hinges. Attached to the ends of this slat are the other two. On one are the sight gauges, and on the other are the scales. The instrument should be set so that the vertical axis measures exactly to the zenith. With it, one can determine the distance of the observed body from the zenith by aiming the slat with the sights at the celestial body and reading the angle measure from the scale. Nicolaus Copernicus described in detail the use of the triquetrum in the fourth book of De revolutionibus in the subsection Instrumenti parallacti constructiono. The instrument was used by the Frombork astronomer primarily to observe the Moon. Danish astronomer Tycho Brahe also used a similar instrument. Until the use of lutetium for sky observations, triquetrum was considered one of the most accurate astronomical instruments.
In the period before 1511, Copernicus recorded 6 observations of the Moon, by 1530, that is, by the time he finished writing De revlutionibus, a total of 12, while the remaining 5 were made between 1530 and 1533. We know where he made most of them: 3 were made in Bologna, 2 in Krakow, 1 in Lidzbark, 1 in Rome, and the remaining 10 in Frombork.
Through the use of the triquetrum, Copernicus determined the parallax of the Moon, i.e. the angle at which he observed the Moon at a particular location on the surface of our planet, relative to the theoretically calculated position if the observer were at the center of the Earth. Through simple calculations, he was thus able to calculate the distance to the Moon, which helped formulate the revolutionary heliocentric theory.
The only observational instrument of Nicolaus Copernicus that has survived to the present day
The only instrument made by Nicolaus Copernicus that has survived to the present day is located in Olsztyn’s Warmia Chapter Castle, where the Museum of Warmia and Mazury has its headquarters. It is a special astronomical table used to observe the path of the Sun in the sky. The astronomer drew it on the plaster of the cloister wall using a gnomonic reflection.
Copernicus made the instrument during his stay at the castle, when he held the office of administrator of the chapter estate (1516-1521). The table measures 705×140 cm and is located on the wall of the cloister of the north wing, just above the entrance to the chamber where the administrator lived. Large sections of this unique work by the Frombork astronomer have survived to this day. Nicolaus Copernicus observed on the wall the reflected light of the sun moving across the sky, drawing lines for dozens of days before and after the equinoxes, drawing them on the wall every five days. The chart was used by Copernicus to determine the timing of the equinoxes and the length of the tropical year, which was crucial to his work on calendar reform. Some researchers see in the table a special form of the sundial, constructed by the Frombork canon.
The 15 lines of the astronomical table reflect the image of the reflection of the Sun’s apparent movement – at five-day intervals – during periods of immediate proximity to the equinoxes. The 14 lines – 9 before and 5 after the equinoxes – marked in red are in the form of hyperbolas. Line 10 marked in blue marks the equinoxes and is a straight line. According to scientists, the letters preserved on this line form the inscription “EQUINOCTIUM.” The black lines on the table are the remains of an unusual daily sundial.
In 2019, a film “Secrets of Copernicus’ astronomy” was produced by the Nicolaus Copernicus Foundation, in which Dr. Jacek Szubiakowski of the Olsztyn Planetarium and Astronomical Observatory explains in detail the secrets hidden on the cloister wall of the Olsztyn castle.
