It's the warmest in the middle of the day for the reason
that the sun typically tends to be brighter at that time. While in the evening,
the sun is getting ready to go down and in the mornings the sun just came up,
so it is not at its highest point so the rays are not as strong. So since the
sun's rays are striking part of the planet straight during noontime, therefore
giving us more heat, but is striking us at a viewpoint at night or in the
morning, therefore giving us less heat.
