The MATER (Latin: "mother") is a circle-shaped container holding all the pieces of the astrolabe. The raised, outer rim of the Mater is the LIMB. The Limb's markings divide the cosmos (here flattened onto its celestial equator) into 360 degrees and 24 hours.

The INDEX (Latin: "pointer") is a simple pointer that makes it easy to read heavenly bodies' coordinates in multiple reference frames. When pointing to the Sun, the Index functions like the hour-hand of a modern clock.

On astrolabes from the Islamic world, a small pointer called AL-MURI is often found in place of the moveable index.

The RETE (Latin: "net") is a decorative framework upon which pointers to bright stars are fastened.

The ECLIPTIC (Greek: "pertaining to eclipses") is an imaginary circle in the sky that tracks the Sun's apparent annual motion. This circle is tilted with respect to Earth's equator by about 23.4°⁠ — a tilt that gives us the seasons of spring, summer, fall and winter. On an astrolabe, this tilt manifests itself as an offset of the Ecliptic circle from the instrument's center. Due to the solar system's disk-like structure, the orbits of the Moon and planets also hew closely to the Ecliptic, with none straying from it by more than ± 9° of ecliptic latitude.

The TYMPANUM (Latin: "drum") is the central disk showing the most important celestial arcs. Since the grid of azimuth and elevation lines is suited to a single latitude only, astrolabes came equipped with multiple Tympana which could be swapped in or out depending on location.

The TROPIC OF CAPRICORN marks the Sun's southernmost orbital excursion and, traditionally, the outermost edge of an astrolabe's map of the cosmos.

The EQUATOR marks the midplane of the Earth-centered celestial sphere. The Sun crosses the equator on the spring and fall equinoxes.

The TROPIC OF CANCER marks the northermost excursion of the Sun as seen from the Earth.

AZIMUTH LINES show compass bearings (north, south, east, west, etc.) for an observer at the specified latitude. Since the astrolabe presents the cosmos from a god's-eye perspective (looking down from above the North Pole), the top of the instrument is south, east is to the left, and west is to right.

ELEVATION LINES, often referred to by their Arabic name, ALMUCANTARS, mark circles at fixed heights from the horizon (elevation 0°⁠) to zenith (elevation 90°⁠) for an observer at the given latitude.

Stars and Sky

Sun

Moon

Planets

CAMPANUS CUSPS divide the sky into twelve symmetric sectors, similar to the wedges of an orange. These sectors evenly divide the observer's east-west azimuth line, also called the PRIME VERTICAL. Due to their symmetry, Campanus cusps are the only cusps which support fractional House coordinates; all other systems define only whole House numbers.

REGIOMONTANUS CUSPS are great circles drawn from the observer's north and south horizons to twelve, evenly-spaced points on the celestial equator. Regiomontanus cusps divide the sky into twelve sectors of unequal sizes.

ALCHABITIUS CUSPS trisect the four quadrants of the celestial equator as defined by the four cardinal points of an observer's sky: ascendant, midheaven, setting, and lower-midheaven.

UNEQUAL HOUR LINES define 12 sectors below the horizon corresponding to the 12 "unequal" or "seasonal" hours of the night. The nighttime hour lines of an astrolabe are equivalent to the first six cusps of the PLACIDUS House system.

PRAYER LINES often appear on astrolabes from the Muslim world since the timings of Islam's five daily prayers are determined astronomically. From left to right these curves indicate Fajr (dawn), Asr (afternoon), Zuhr (mid-day), and Shafaq (twilight). The Sun's position is found by joining, via the astrolabe's index, a point on these curves to a corresponding point in the astrolabe's upper-right (western) quadrant.