Star trails are arithmetic. Find the pole, point at it, and let the planet do the composition. The only creative decision left is what you put underneath.
Forty frames at thirty seconds each, stacked. Stacking beats one twenty-minute exposure because a single frame that long will cook the sensor and any passing aircraft ruins the whole thing rather than one-fortieth of it.
The rock was lit by a half moon behind me. No torches, no light painting — moonlight is a big soft source and it is free.