If you think that we are cold in winter because that is when Earth is farthest from the sun (as a study showed many Harvard students believe), then you will be surprised to know that today is Perihelion, the day of the year when the Earth is closest to the sun. (Aphelion, the point on the orbit farthest from the sun, occurs in July).
Our cold and warm seasons are caused by the tilt of the Earth relative to the orbital plane, so that in winter the Northern Hemisphere is tilted away from the sun and in summer it is tilted towards the sun. When the sun is tilted away, the days are shorter and the solar energy we do get is less direct, leading towards cooler temperatures.
Here’s a link to a brief explanation from Lee Haywood at WSAV in Savannah (link).
Now you can say you are smarter than a Harvard student!