
accessory: used here to refer to any associated parts of an instrument such as tripod base and legs.

age of the moon: number of days that have passed since the previous new moon.

alidade: straight rule with sights. An alidade could be used for surveying with a plane table but it also appears in a different form as part of an astrolabe.

almucantars: lines of equal altitude on a projection of the heavens based on the local horizon.

altazimuth theodolite: theodolite for measuring altitude and azimuth simultaneously, see article on the theodolite.

altitude: angle above and perpendicular to the horizon, or an angular elevation above the horizontal direction in the same azimuth.

altitude dial: sundial measuring time from the altitude of the sun.

armillary sphere: set of rings corresponding to the circles of the celestial sphere, see article on the armillary sphere.

aspectarium: aidememoire which depicts the astrologically significant angles (or aspects) between the planets.

astrolabe: astronomical instrument based on a planispheric projection of the heavens, see article on the astrolabe.

astrolabe quadrant: quadrant that has many of the lines and functions of the ordinary astrolabe, projected for a single latitude.
