sextant

Optical instrument for measuring the angle between a heavenly body and the horizon to determine the ship’s position.

drum

Thumbnail for turning the micrometer screw.

horizon shade

Colored glass that blocks certain rays in the light spectrum to filter out ambient light.

micrometer screw

Screw with a head graduated in minutes that is turned to set the index arm precisely.

vernier scale

Small graduated rule that slides along the ruler and is used to read very precise measurements.

graduated arc

Arc graduated in degrees; the observed angle measurement is read from it.

frame

Support for the various components of the sextant.

horizon mirror

Fixed mirror in front of the telescope; it is aimed at the horizon and the image of the Sun is projected on it.

index shade

Colored glass that blocks certain rays in the light spectrum to filter out ambient light.

telescope

Optical instrument that magnifies an observed object.

lens hood

Device attached to the telescope’s eyepiece that shields the eye from light coming from the source and from strong ambient light.

index arm

Moving arm on the sextant that measures the displacement angle on the graduated arc to determine the height of the observed heavenly body.

index mirror

Mirror integrated with the index arm that is positioned so that the Sun reflects on the horizon mirror.

index

Guide mark that helps to read the graduation marks on the arc.