Here's why:

* Directions and Circles: Imagine a circle representing the Earth. If you stand at a point and look towards the east, then continue moving in that direction, you'll eventually complete a full circle and end up back where you started.

* Degrees: A circle is divided into 360 degrees. Therefore, moving halfway around the circle is 180 degrees.

* East to West: Moving from east to west (or vice versa) means going exactly halfway around the circle.

Therefore, east and west are opposite directions and are 180 degrees apart.