Sextants can be used very accurately to measure other visible angles, for example between one heavenly body and another and between landmarks ashore. Used horizontally, a sextant can measure the apparent angle between two landmarks such as a lighthouse and a church spire, which can then be used to find the distance off or out to sea (provided the distance between the two landmarks is known). Used vertically, a measurement of the angle between the lantern of a lighthouse of known height and the sea level at its base can also be used for distance off.
sextants can be used very accurately to measure other visible angles for example between one heavenly body and another and between landmarks ashore used horizontally a sextant can measure the apparent angle between two landmarks such as a lighthouse and a church spire which can then be used to find the distance off or out to sea (provided the distance between the two landmarks is known) used vertically a measurement of the angle between the lantern of a lighthouse of known height and the sea level at its base can also be used for distance off