You might expect that the Earth would be the coolest when it is farthest from the sun. But that date is today, and it is certainly not a cold day. This is known as the aphelion (I remember it as “A for away”) and it occurs because the earth’s orbit around the sun is not perfectly circular but is an ellipse, so at times the sun is a little closer (currently in Northern Hemisphere winter, an event called perihelion) and at other times the sun is a bit farther away, such as today.
It turns out the difference between aphelion and perihelion causes only small differences in incoming sunlight, and the real determining factor for our seasons is the tilt of the earth’s axis of rotation towards the sun in NH summer and away from it in NH winter. That changes the incoming sunlight much more than the small differences due to the Earth’s orbit. You can read more about the aphelion at Space.com here.
