This image was on NASA's website recently:

It's a real depiction of something happening right now, but apparently there's no need to resort to Douglas Adams to explain it -- or maybe there is:

Have you ever been hit by a beam of high energy particles from above? Surely you have -- it happens all of the time. Showers of high energy particles occur when energetic cosmic rays strike the top of the Earth's atmosphere. Cosmic rays were discovered unexpectedly in 1912. ... Although many of the low energy cosmic rays come from our Sun, the origins of the highest energy cosmic rays remain unknown and a topic of much research. This drawing illustrates air showers from very high energy cosmic rays. Cosmic rays may even be important to Earth's weather -- common lightning may be triggered by passing cosmic rays.

If I recall correctly, didn't the Vogons provide some sort of unintelligible advance warning?