The common 50 minute rule
On average, moonrise happens about 50 minutes later from one day to the next. The reason is orbital motion. While Earth rotates once, the Moon has moved eastward along its orbit, so your location has to rotate a bit more before the Moon reaches the same place in your sky.
Why it is only an average
The actual change can be much smaller or larger than 50 minutes. The Moon’s orbit is elliptical, so its apparent speed changes. Its path also crosses the horizon at different angles depending on phase, declination, season, and latitude.
When the Moon’s path meets the horizon at a shallow angle, small position changes can create a large timing shift. When it crosses more steeply, the timing shift can be smaller.
The full Moon exception people notice
Near the autumn full Moon in the Northern Hemisphere, successive moonrises can be closer together than usual for some latitudes. This is the geometry behind the traditional Harvest Moon effect. The Moon’s path makes a shallow angle with the evening horizon, so it rises not much later on consecutive evenings.
