Generally, being out on the surface wasn't much of a problem, so why was today any different? 

Ren shivered in the thin atmosphere as he looked around in puzzlement.  Surely the sky should be much lighter than this.  Had he come out through the wrong tunnel?  No, there was Mount Credan, as angular as ever, with its topping of white snow, but looking subdued in the scanty light.

Scared, he turned to his companion.  'Father.  Why is the land so dark, and where is the sun?'

'Do not fear, my son.  Our companion planet Thoros is directly between the sun and us.  When it moves along its orbit, the sun will reappear, and the light will return to us.  This happens very rarely, and never before in your lifetime.  I was not much older than you when I last saw this marvel.'

'It's scary, Dad.  Why did you bring me out here to frighten me?  I want to go back to the cavern.  I don't like it out here; its too cold.'

'You must see it for yourself Ren, so that you can show it in turn to your children.  The star mappers will tell you and your generation when to expect it, like they did with me, so that all will know that it is a natural event, and not to be feared.'  He smiled fondly at his offspring.  'There are many more people like us who have come out to watch it tonight.  Some of them have never left the warmth of the caverns before tonight.'

'And what is that ball of fire streaking through the skies?  What do the star mappers tell you of that?'

'I don't know, son.  They have never described anything like this before.  It looks like it's heading for the place where the sun should be.  It's not going to hit us, so there is nothing to be afraid of.'

Colomet put his arm around his son's shoulders, and guided him to a soft sandy spot so they could sit and await the return of the light.

Chatting quietly, they sat and watched the ball of fire moving across their field of vision.  The massive explosion as the stray comet slammed into the planet Thoros barely had time to register on their minds before the resulting shock wave stripped the atmosphere from their own planet, snuffing out all life on the surface of the world.  Dwellers in the deep caverns living behind airtight doors survived for a few hours more, not comprehending why all communications from all over the planet had ceased.

There were no eyes left to see how the shattered pieces of the ruined planet settled into a wide orbit around their sun.  No eyes left to see how a large chunk of the planet collided into the blue green world closer into the sun, snuffing out the large dinosaurs roaming its surface.  

 No eyes left to see the return of the light.