Answer :
Final answer:
The hour lines on a hemispherical sundial are designed to indicate the time of day by aligning with the shadow cast by the central gnomon, which changes with the seasons.
Explanation:
The purpose of the hour lines on a hemispherical sundial is to indicate the time of day. These hour lines are scribed into the sundial to correspond to different seasons because the Sun's path in the sky changes throughout the year, affecting the position and length of shadows. Depending on the time of the year, the shadow cast by the central vertical gnomon will align with different hour lines on the sundial, thus allowing people to tell the local apparent solar time observationally.
The Romans designed their sundials to use the position of the Sun at local noon, which was determined when the shadow cast by a gnomon was at its shortest. Sundials, including more advanced versions like the hemispherical dial with a vertical gnomon, essentially translate the motion of the Sun into a timekeeping mechanism. The concept has its roots in agricultural societies and was key to the design of earlier mechanical clocks, setting them to run clockwise, mirroring the shadow's motion on a sundial.
