Almucantar
An almucantar is a circle in the sky that runs parallel to the horizon. Stars on the same almucantar share the same altitude above the horizon. The word comes from Arabic and was brought into European astronomy in the Middle Ages.
An almucantar staff is a simple instrument used to tell the time at sunrise or sunset and to find the sun’s height. It’s a type of backstaff: a shadow from a vane on a horizon line is aligned with a sighting vane, and by reading the angle between them you get the sun’s altitude.
In science, the almucantar plane that contains the sun helps researchers study how aerosols scatter sunlight. Measurements are taken at several angles on both sides of the sun to learn about aerosol properties. Two well-known methods for this are Dubovik’s approach used in NASA’s AERONET network and Nakajima’s SkyRad method.
This page was last edited on 2 February 2026, at 18:15 (CET).