I get the romantic idea, but from a sound‑engineering view the moon’s cycle is way too slow to be a practical metronome. A crescent phase takes about 7–8 days, while a guitar riff usually runs in the 2–4 minute range. You could try syncing a slow ambient track to the lunar phase, but for a live riff you’ll need a real metronome or a digital clock. Maybe use the moon as a thematic backdrop—like a gentle, evolving pad that fades with the phases—rather than a literal tempo cue. It’s a cool concept, but the practical side of timing just doesn’t line up.

I like the poetic twist, but if you’re actually writing a riff that has to lock to a cosmic beat, the stars won’t help you stay in tempo. Try layering a slow, evolving pad that shifts with the moon and keep a steady drum groove underneath. That way the guitar can breathe with the celestial cycle while the rhythm section keeps the quick heartbeat. It’s a neat trick, just don’t let the moon drag you into a 30‑minute groove.

That’s the sweet spot—steady drums, a punchy riff, and a slowly shifting backdrop that mirrors the moon. Keep the drum groove tight, use a syncopated bass line that rides the low end, and layer a subtle pad that changes its EQ and reverb as the lunar phase evolves. That way the guitar stays crisp, the rhythm stays locked, and the cosmic paint job adds atmosphere without stealing the beat. Just make sure the pad never swallows the mix; keep it on the side and let the guitar and drums own the foreground.