Cats sleep about 13-16 hours a day, although particularly lazy cats might average between 18-20. Twenty minutes after a two hour nap, they collapse on your favorite chair in exhaustion, ready for another snooze session.
The big question on everyone's mind is why. Why do cats sleep so much? You'd think for a species bent on taking over the world, they'd dedicate more of their time and resources to, you know, world domination and stuff.
When people sleep, they sleep deep. My mother often jokes about how a bomb could go off right outside my window and I wouldn't so much as roll over. She's probably right. For cats, it's a little different.
For the most part, cats sleep very lightly. If you touch a cat, his head will pop right up and he'll be wide awake. Their ears rotate and register all the sounds that go on around them. They're very much aware.
Now, I'm going to let you in on a little secret: Believe it or not, cats only need to sleep for two hours a day. The rest of the time? It goes to charging the mother ship.
When you see a cat curled up with its eyes closed and you poke it and it doesn't budge (but it's breathing!) and you wiggle it some more and it still doesn't respond, it's the cat getting its 40 winks. When it's in that light-sleeping stage though, all the energy it gains from rest is going into space.
Part of the reason that our own space program isn't as advanced as we like to imagine it in science fiction is that launching and propelling a craft through space requires massive amounts of energy, which we only know how to provide with fuel and water (solar power is still in the works). The reason cats have been able to travel to other planets is in part due to their ingenious ways of harvesting energy - through the little aliens themselves.
When a cat does its so-called "sleep," it's really radiating a unique form of energy that the mother ship picks up on. Now, in a single nap, a cat may only give off enough energy to power a light bulb, but when you combine all the energy of all the millions of cats on this planet, well then, it looks like you're going places.