Constellations Thesis Book by Nesrin Zidan

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• Gnomon: Utilizing the length of the
sun’s shadow as a gauge for latitude, this
was the earliest version of a sundial.
• Sea Astrolabe: By measuring the altitude
of the sun at noon (declination)
or the meridian altitude of a star with a
known declination, the marine astrolabe
was an inclinometer used to approximate
the latitude of a ship at sea. It was used by
sailors in the Middle Ages (1470). It was
a metal disc that had a ruler and scale on
it. Sailors might estimate the distance to
celestial bodies by holding a disc at eye
level from a ring at the top and adjusting
a ruler (Can you name 10 tools we used
to navigate the seas before ECDIS? 2017).
The idea predates the Roman Empire, and
it has been believed that Hypatia of Alexandria,
a female mathematician, and philosopher
who lived in Egypt in the fourth
century AD, was the creator of it. Moreover,
during the Middle Ages, the astrolabe
was well-known in the Islamic world.
It was a reduced version of an instrument
first created by Arab astronomers to gauge
the height of celestial bodies over the horizon
(What is a Mariner’s Astrolabe?).
Fig. 3.1. Gnomon and how it tells time
Fig. 3.2. A Sea Astrolabe and how to
wield it