An ancient instrument
for solving problems relating to time and the position of the Sun and stars in the sky.
It had many uses, including
telling time during the day or night, finding the time of sunrise
and sunset and, thus, the length of the day, and locating celestial
objects in the sky.
It was widely used until replaced by the
→ sextant. The → planispheric astrolabe,
which is the most common type of the instrument, is typically made up of a
graduated disk hanging vertically, which is rotated so that it can be
directed to the star chosen. The local time can thus be read from the
face of the astrolabe, and different tables, at various latitudes,
can be used. More specifically,
a planispheric astrolabe is made up of the following main components:
→ mater,
→ tympanum,
→ rete,
→ alidade,
→ throne,
→ limb,
→ pin,
→ horse,
→ front, and
→ back.
The astrolabe was invented by Greeks, and some historians have attributed it to
Hipparchus (c190-c120 BC). Modern, sophisticated versions
(such as → prismatic astrolabe and
→ Danjon astrolabe), are used for high precision measurements
of star positions. See also → particular astrolabe,
→ spherical astrolabe, and
→ universal astrolabe.
Etymology (EN): M.E., from O.Fr. astrelabe, from M.L. astrolabium, from Gk.
astrolabos (organon) “star taking (instrument),” from
astron “star,” → astro- + lambanein “to take.”
Etymology (PE): Ostorlâb, from Ar. usturlab, from Gk. astrolabos, as above.
