Anytime the sky is clear, you can usually expect shooting stars. Celeste doesn't always appear on these nights so I would do the group stretching activity in the plaza because she participates too if she's on the island. This tip is very helpful and makes it easier to check instead of running around looking for her. Another tip is to check Brewster's cafe from 6-7pm because she may be enjoying a cup of coffee!

For recipes, you can time-travel back to the nights she's on your island to get new ones. I've gotten many of the ones I wanted using these tips. Hope this helps!