The 555 timer takes the ramp signal from an RC circuit and converts it to a square wave signal. The signal goes from 0 to VCC, if the signal is slow enough (less than 30 Hz) you can see the LED blinking.
However, if you want to use the ramp signal, it will give the LED a Fading in and out apperance. See this circuit for more info
**broken link removed**
I myself have used that circut and it is visually Appealing.
(the above needs grammer checking, its 3:30AM in the morn.. But you get the idea)