When I was still a junior secondary student, I was tricked by a senior. She asked me: Could you jump over your own shadow? My first thought – it was all about length. I could definitely jump over my own shadow when it is short. So, I tried to find out when the length of my shadow would be the shortest. I went to the rooftop at different times and recorded the length of my shadow. I got what I wanted – it was the shortest at noon when the sun was right above me.

After this, my focus gradually shifted from jumping over the shadow to studying the relationship between the length of the shadow and time. Later, I also noticed the length of the shadow varied with different months in a year, even if the measurement was taken at the same moment in a day. The shadow in summer is always shorter than it is in winter.

This scientific principle is exactly the theoretical base of an ancient astronomical instrument called the Gnomon. The ancient Chinese used this device to define the 24 solar terms. Farmers in the past used the 24 solar terms to determine sowing and harvesting times. That's why I say Gnomon is an astronomical instrument that can influence food production!

Let's think
In Hong Kong, every year there are two days that everything casts no shadow at around noon time. This phenomenon called "Lahaina Noon", do you know why this happens?