Founders of Geodesy and Astronomy: Eratosthenes and Hipparchus

Flashcards based on the lecture notes covering the contributions of Eratosthenes and Hipparchus to geography, astronomy, and cartography.

Eratosthenes (276–194 BC)

A Greek mathematician, geographer, and astronomer known as the first scientific geographer who calculated the length of the equator and developed a system of latitudes and longitudes.

Geodesy

A field of study for which Eratosthenes is considered the founder, involving the measurement and representation of the Earth.

Gnomon

An indigenous apparatus or vertical staff used by Eratosthenes and other Greeks to observe heavenly bodies, measure the position of the Sun, and determine latitudes and longitudes.

Syene (Aswan)

The location of a deep well where the Sun's image was reflected at the bottom during the summer solstice, indicating the Sun was directly overhead.

Theorem of Thales

The geometric principle used by Eratosthenes to calculate Earth's circumference, stating that when a diagonal line crosses two parallel lines, the opposite angles are equal.

Circumference of the Earth (Eratosthenes)

Calculated as $25,000\,\text{miles}$ by multiplying the estimated distance between Syene and Alexandria ($500\,\text{miles}$) by $50$ ($1/50$th of a circle).

Ekumene

A term describing the inhabited earth as detailed in Eratosthenes' writings, which included three major divisions (Europe, Asia, and Libya).

Five Climatic Zones

Eratosthenes divided the Earth into one torrid zone, two temperate zones, and two frigid zones.

Taprabone

The ancient Greek name for modern-day Ceylon (Sri Lanka), which Eratosthenes placed south of Coniaci.

Hipparchus (190–120 BC)

A Greek astronomer and mathematician considered the founder of trigonometry and famous for discovering equinoxes and compiling the first star catalogue.

Star Catalogue

A monumental achievement by Hipparchus in $129\,BC$ listing about $850$ stars with brightness specified by a system of six magnitudes.

Climata

The term used by Hipparchus to describe the belts of latitudes into which he divided the world.

Astrolabe

An instrument invented by Hipparchus for determining latitudes and longitudes that was more accurate than the gnomon and useful for navigation at sea.

Stereographic Projection

A map projection devised by Hipparchus where a flat parchment is laid tangent to the earth and lines are extended from a point opposite the point of tangency.

Orthographic Projection

A map projection designed by Hipparchus produced by projecting lines from a point in infinity to convert the curved sphere into a plane surface.

Assyrian Arithmetic (360 Degrees)

The mathematical basis used by Hipparchus to be the first to divide a circle into $360$ degrees.