How come we get sunburnt?

Question

How come we get sunburnt? The sun is 93 million miles away. I go 1,000 miles south and I get burnt like a lobster. That just does not make any sense to me. After 93 million miles you would think 1,000 miles south would not make that big of a difference.

Answer 1

The reason why the sun gets stronger the closer you get to the equator is not to do with the difference in the distance from the sun, but the angle of the incoming rays and how that affects the amount of energy delivered to a given unit area.

It's a little easier to picture with a simplified model. Imagine shining a torch beam at a beach ball. If you shine it at the ball's "equator", the beam is more or less round where it strikes the surface of the ball. If you point that beam up at the "pole", the round shape gets stretched out into an oval shape that covers a larger area. The amount of light the torch emits hasn't changed, but at the poles it is more spread out and therefore not as bright. A similar principle applies with the sun on Earth - at the equator the sun is high in the sky and the incoming "rays" packed tightly together, carrying a lot of energy per square metre. As you move further from the equator, the sun doesn't get up so high in the sky, so the "rays" come in at a shallower angle, get spread across a wider area and carry less energy per square metre. The diagrams on the article linked in sources should make it clear what happens when the sun is at different angles to the ground.

This applies to all the radiation the sun emits - the heat in the form of infra-red, the visible light, and the ultra-violet rays, which are what cause sunburn.

Answer 2

Solar radiation is sent out from the Sun towards the Earth. Ultraviolet light is responsible for sunburn. Even though ozone absorbs a large quantity of UV light, some manages to reach the surface of the Earth. UV light basically destroys skin cells because of its high energy. The number 93,000,000 only means we won't be fried by the Sun.