Stars twinkle because of our air, not because they flicker. Sometimes the shake is in the view, not the thing.

Starlight is steady the whole way here and then wobbles in the last few miles, through the air you are breathing. What looks like instability in the star is instability in the medium you are looking through. Your own view has weather too: tiredness, hunger, a bad morning, a sore result. Things look unsteady when the air between you and them is moving.

Before deciding something has gone wrong, check the atmosphere you are reading it through. Did you sleep, have you eaten, is it eleven at night? Look again after a meal and a night’s rest and see whether the flicker is still there.