How does an astrolabe work?

Question

How does an astrolabe work?

Answer 1

it was a type of early scientific instrument used for reckoning time and for observational purposes. Astrolabes can be traced to the 6th century AD; they came into wide use in Europe and the Islamic world in the early Middle Ages and were adopted by mariners by the mid-15th century. One widely used variety, the planispheric astrolabe, can be regarded as a rudimentary analog computer. It enabled astronomers to calculate the positions of the Sun and prominent stars with respect to both the horizon and the meridian

Answer 2

it was a type of early scientific instrument used for reckoning time and for observational purposes. Astrolabes can be traced to the 6th century AD; they came into wide use in Europe and the Islamic world in the early Middle Ages and were adopted by mariners by the mid-15th century. One widely used variety, the

planispheric astrolabe, can be regarded as a rudimentary analog computer. It enabled astronomers to calculate the positions of the Sun and prominent stars with respect to both the horizon and the meridian.

Answer 3

"Most astrolabe problems were solved using the front of the instrument. The front of an astrolabe has two types of parts: fixed and rotating. The fixed parts represent time scales and the stereographic projection of the sky as seen from a specific latitude. The rotating parts simulate the daily rotation of the sky."

http://astrolabes.org/parts.htm

"To use an astrolabe, you adjust the moveable components to a specific date and time. Once set, the entire sky, both visible and invisible, is represented on the face of the instrument. This allows a great many astronomical problems to be solved in a very visual way."

"Typical uses of the astrolabe include finding the time during the day or night, finding the time of a celestial event such as sunrise or sunset and as a handy reference of celestial positions. Astrolabes were also one of the basic astronomy education tools in the late Middle Ages. "

"The typical astrolabe was not a navigational instrument although an instrument called the mariner's astrolabe was widely used. The mariner's astrolabe is simply a ring marked in degrees for measuring celestial altitudes."

http://www.astrolabes.org/

Mariner's Astrolabe

It was not possible to determine longitude at sea in the early days so the Mariner's Astrolabe was used to determine the latitude of a ship by measuring the noon altitude of the Sun.  The Sun's declination for the date was looked up in an almanac (sometimes the charts were actually etched onto the brass astrolabes). The latitude is then 90° - measured altitude + declination .

http://astrolabes.org/mariner.htm