Oblique differences in sun’s rays
IN THE northern hemisphere’s winter the Earth is closer to the sun, so why is it colder than summer?
Imagine a beam of sunshine as wide as the planet. When it reaches the planet some rays will strike the Earth full on, but as you go further north or south, the angle becomes more oblique. The more oblique that angle, the larger the area that that unit of the sun’s energy is spread around, which means those places will be less warm.
The angle is most oblique at the poles, making them the coldest areas on Earth.
There are two complicating factors: the tilt of the Earth, and its slightly elliptical orbit around the sun – the Earth is about 3% closer to the sun in January than in July.
The planet is also tilted roughly 23.5ºC to the imaginary vertical line running from the North to the South Pole.
As we orbit, the direction in which this imaginary line is pointing changes gradually, like a spinning top whose spoke is slightly off-vertical.
As the Earth orbits the sun, gradually the area which receives the most heat changes. Near the equator, there are no great seasonal differences in temperature. As the sun’s rays strike almost full-on all year round, it constantly experiences high temperature.
The temperature is thus an interplay of two factors: our distance from the sun, and which hemisphere is tilted towards it.