1. A celestial body's movement across the meridian of a place. Also known as meridian transit.

2. Passage of a smaller celestial body across a larger one.

3. Passage of a satellite's shadow across the disk of its primary.

1. A surveying instrument with the telescope mounted so that it can measure horizontal and vertical angles. Also known as transit theodolite.

2. To reverse the direction of the telescope of a transit by rotating 180° about its horizontal axis. Also known as plunge.

A positive-fixing system employing low-orbit satellites which constantly emit continuous-wave signals; on the surface vehicle, the signals are received and the Doppler shift is recorded; position is determined by computation based on the shift.