Vertical circle (instrument)

It is a device for measuring astronomical angles, which can be rotated in altitude and azimuth.

[1] It consists of a telescope (in astronomical geodesy occasionally also with a reflecting telescope), which is mounted on a horizontal tilting axis and is supported by a stable altazimuth mount.

It is similar in design to the meridian circle, but the latter only has a horizontal tilting axis without the means to change azimuth.

The angular movements around the tilting and standing axes are measured with large, finely divided circles and a reading microscope.

However, in the 19th century it was more basic with observatories often making recording of coordinates of different items and to determine the shape of the Earth and times.