Here's why:

* Earth's Tilt: The Earth is tilted on its axis, and this tilt is the primary reason for seasons. During winter in the polar regions, the Earth is tilted away from the sun, causing the sun's rays to strike the surface at a very shallow angle.

* Spread of Energy: When sunlight hits at a low angle, the same amount of energy is spread over a larger area. This means that each square meter of the Earth's surface receives less energy, leading to lower temperatures.

* Longer Path Through Atmosphere: Sunlight has to travel through more of the atmosphere when it hits at a low angle. This leads to more scattering and absorption of the energy before it reaches the surface.

This low angle of incoming solar radiation is a key factor in the extremely cold temperatures experienced in polar regions.