In celestial navigation, a mathematical expression describing a direction in space with relationship to a space vehicle. A bearing measures the angular difference between the current forward direction of the spacecraft and the direction being described.

The first number in a bearing describes an azimuth in degrees, and the second describes an elevation. For example, a bearing of 000 mark 0 describes a direction directly ahead of the vessel. A bearing of 330 mark 15 describes a direction to the port side (left) of the ship, somewhat above the centerline of the vessel.