In The Sky
Practical measurement and astrology often followed twin paths. The astrolabe served to find the positions of stars, Sun or Moon, the time of day, latitude at sea and also for astrological calculations. The invention of the telescope allowed more precise observations using instruments such as the transit, linking movements of stars across the meridian to calculations of exact time.
Suspending an astrolabe by the ring at the top, the observer used the adjustable sighting rule to establish the position of a celestial body, and the central astronomical markings for calculations.
Transit instruments like this one, with the telescope suspended to swing vertically, were designed for observing stars as they cross the observer’s meridian, a guide to deriving the exact time.