Here's why:

* The angle of the sun: The sun is at its lowest point in the sky at sunrise and sunset. This low angle creates a longer shadow than when the sun is higher in the sky.

* The position of the sun: As the sun rises, it climbs higher in the sky, decreasing the length of shadows. The same happens in the evening as the sun sets.

So, if you want to find the longest shadow, look for it at the beginning and end of the day!