Several circuits I've seen use an opto-isolator or a transistor between the 555 output and the triac gate, i.e. or .
The triac I'm using has a 50mA gate current and the 555 can sink and source 200mA. The triac will be controlling a non-inductive AC load where the AC voltage will not exceed 18V (coming from a bicycle dynamo), so there is no shock hazard here.
Can anyone think of a reason I need that extra component between pin 3 of the 555 and the triac gate? I was just going to put in a current limiting resistor of 10 ohms or so.