Vertical Circle Explained

Astronomy uses a number of terms which may not be understandable to an average reader. In this article, we will explain the term ‘vertical circle’ as well as several closely related terms.

Vertical Circle Definition

Vertical circle is defined as a great circle on an imaginary sphere enclosing the Earth or celestial sphere at a 90 degrees angle to the horizon, which means that it passes through both poles of the horizon - nadir and zenith. Since vertical circle is aligned with the horizon at an angle of 90 degrees, there is a vertical circle for every azimuth on the north-east direction of the horizon. However, vertical circle can also be on the east-west direction. But in this case, it is known as the prime vertical. When it is on the north-south direction, it is referred to as the principal vertical or the Local Celestial Meridian (LCM).