Why is winter cold?

Answer

Our earth is approximately 93 million miles from the sun. Its orbit is almost circular but slightly elliptical. The earth orbits the Sun at an angle or tilt of 23.5 degrees.

This angle causes some parts of the earth to be farther from the sun and some nearer to the sun than others at certain times of the year.

Winter arrives when that part of the earth is tilted away from the sun and the sunlight is spread over a greater area, and therefore the heat energy reaching earth's surface is less than in summer.