Nacreous

You see this shooting across the sky at twilight. (Click to open a larger view in a new window.)

Some questions to think about if you need a jump start:

What is it?
What has caused it?
What will happen?

Or who is it?
Where are they going and why?
Are they chasing something or being chased?
Are they off to the rescue or off to some big event?

(The original is at Nacreous Clouds - Southern Norway, along with other cool nacreous cloud pictures.)