Chen Liguo (middle), a teacher of sciences at Hangzhou Binxing School, delivers a lecture on June 21. [Photo/hangzhou.com.cn]

Chen Liguo, a teacher of sciences at Hangzhou Binxing School, gave a lesson on Summer Solstice with the school's sundial on June 21, the day of Summer Solstice.

A sundial is a device developed by ancient Chinese and used for telling the time when the sun is shining. The shadow of an upright rod falls onto a flat surface that is marked with the hours.

The sundial is located at the Hangzhou Binxing School. [Photo/hangzhou.com.cn]

The history of the sundial can be traced back to the Spring and Autumn Period (770-476 BC). 

Chen said that in the noon of Summer Solstice, observers will find that the shadow of the sundial's rod is the shortest throughout the year.