How did the ancient Greeks study stars?

Answer 1

The ancient Greeks developed instruments such as the armillary sphere to track the movement of objects in the plane of the celestial equator against the annual motion of the Sun. This basic device consisted of a set of graduated rings that represented important circles on the celestial sphere, such as the horizon, the celestial equator, the ecliptic, and the meridian. These rings formed a skeletal celestial sphere. A movable sighting arrangement allowed early astronomers to observe a celestial object and then read off its position using the markings on the relevant circles.

Ptolemy and other Greek astronomers used the quadrant, a graduated quarter of a circle constructed to allow an observer to measure the altitude of celestial objects above the horizon. An astronomer would sight a target celestial object along one arm of the quadrant and then read off its elevation from a scale (from 0 to 90 degrees) with the help of a plumb line suspended from the center of the quarter circle. With this arrangement a celestial object just on the horizon would have an elevation of 0 degrees, while an object at zenith would have an elevation of 90 degrees.

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