The sun’s rays are parallel!

I don’t often post on science-related topics, but I thought it would be fun for a change.

It can be difficult to wrap one’s head around the idea that the rays of light reaching us from the sun are (almost) parallel to each other. Look, for instance, at the following picture of a sunset (borrowed from the web).

They certainly don’t look parallel. However, if you draw a sketch of the earth-sun system that is vaguely to scale, you have to admit that it must be true:


The reason the rays of a sunset do not look parallel is because of the way our eyes work. Things further away look smaller and closer together than they do when viewed up close.

Yesterday, I took a photograph that essentially proves that the sun’s light rays are, in fact parallel:


This photo was taken while looking due east, in exactly the opposite direction to the sunset. What you see here are not light rays spreading out from the sun, but rays coming back together on the opposite side of the sky. They can only do this if they are parallel.

It’s a bit like standing under a set of parallel telephone lines (excuse the rough artwork!)

phone-lines-mainIf the person looks to his left, as he is shown doing in the above picture, this is what he sees:

phone-lines-leftThe phone lines converge toward a single vanishing point in the distance. If the person looks to his right instead, this is what he sees:

phone-lines-rightOnce again, the phone lines converge toward a vanishing point. So, for a set of parallel lines, there are two vanishing points, each at the opposite end of the sky from the other.

A set of lines that are not parallel will have at most one vanishing point, but not two. My photograph, then, proves that the light rays from the sun are, indeed parallel.






3 Responses to The sun’s rays are parallel!

  1. L.Long says:

    Well you may not do this often but you did it well and the drawings are pretty good too.

  2. Sabio Lantz says:

    Fun write-up. But even in your sun-earth drawing, those aren’t parallel lines. But the perception point is important.

  3. Keith says:

    Indeed, the sun’s rays are never, in reality, exactly parallel, as the sun-earth sketch demonstrates. This simply isn’t possible for rays emitted from a (virtual) point source. But they’re close enough to parallel for most practical purposes.

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