In the winter, the sun is lower in the sky. The light is indirect because the light strikes the earth from a lower, shallower angle, a glancing blow. Because of this lower angle, the same amount of sunlight is spread out. Any particular area on the earth receives less sunlight, because the light is spread out over more earth, because of this lower angle. Another result, of the sun being lower in the sky, is that the days are shorter.
Sunrise is later, and sunset is earlier.
This gives the sun less time to warm the earth. Winter in the southern hemisphere happens during the northern summer. See the first diagram. The earth is slightly farther away from the sun, during the southern winter. Yes, more or less.