This diagram shows the beams of sunlight hitting the Earth during a day of a solstice. In this particular solstice, the Northern Hemisphere would be in summer because the sunlight is coming in almost directly overhead in the middle latitudes (the black sticks represent the orientation of a person standing at the observation latitudes). To the observer in the Northern Hemisphere, at noon the sun would appear to be relatively high in the sky (see inset), meaning the solar altitude is high, and so the incoming sunlight intensity would be high at this moment.

In the winter hemisphere, the sunlight comes in at a relatively shallow angle, so the solar altitude is smaller and the sunlight intensity is smaller also. Notice how the shadow of the brown stick is longer when the sun is low in the sky in the winter--the length of the shadow gives an indication of the solar altitude.