Danger or Clearing Bearings
Many ports have provided leading lights or shapes to guide mariners safely into harbour, avoiding shoals and other dangers.
In places where such aids are not provided, the navigator may still be able to select a leading line provided by the transit of natural features. Thus approaching an anchorage with a coastal hill in transit with a more distant peak may ensure that the vessel clears dangerous rocks.
The advantage of a transit is that the mariner is assured of a safe approach regardless of any compass error
Vertical Sextant Angle
The distance off a light can be found by taking the vertical angle the light subtends at the vessel above sea level.
