Observing the Night Sky: The Birth of Astronomy

A collection of vocabulary flashcards covering key concepts in astronomy and ancient astronomy.

Celestial Sphere

An imaginary sphere surrounding Earth, with stars and celestial objects fixed on its surface.

Geocentric Model

Ptolemy’s model positioning Earth at the center of the universe with celestial bodies orbiting it.

Ecliptic

The circle in the sky that the Sun appears to trace over the course of a year.

Zenith

The point directly overhead an observer.

Horizon

The line where the sky meets the ground.

Celestial Poles

The points in the sky that the celestial sphere rotates around, aligned with Earth's axis.

Circumpolar Zone

The region of the sky around the North or South Pole where stars are visible year-round.

Diurnal Motion

The apparent daily motion of stars, the Sun, and the Moon caused by Earth's rotation.

Retrograde Motion

The apparent backward motion of planets observed in the sky, explained by epicycles.

Eratosthenes

The ancient Greek mathematician who estimated the Earth's circumference using angles and shadows.

Precession

The slow wobbling motion of Earth's axis, taking about 26,000 years for a complete cycle.

Ptolemy

An ancient astronomer who developed a comprehensive geocentric model in his work Almagest.

Magnitude System

A classification system established by Hipparchus to rank stars based on their brightness.

Astrology

A belief system that suggests planetary positions affect human actions, considered a pseudoscience.

Heliocentric Model

Copernicus's model proposing that the Sun, rather than the Earth, is at the center of the universe.

Galileo Galilei

A key figure in the development of modern astronomy, known for his telescopic discoveries.

The Meridian

The great circle passing through the celestial poles and the zenith of an observer's location.

Latitude

The measure of how far north or south one is from the equator.

Circumference of the Earth

Eratosthenes calculated this to be about 39,400 km, quite close to the modern value.

Constellation

A recognized pattern of stars, historically linked to mythology and used for navigation.

Asterism

A recognizable pattern of stars that does not constitute a constellation.

Apparent Motion

The perceived trajectory of stars due to the Earth's rotation.

Fixed Stars

Stars that maintain their positions relative to one another over time.

Wandering Stars

Celestial bodies, such as planets, that move relative to the fixed stars.

Zenith

The highest point in the sky directly above an observer.

Celestial Equator

An extension of Earth's equator onto the celestial sphere.

Ancient Greeks

Cultured societies that made significant astronomical observations and models.

Almagest

Ptolemy's treatise that summarized the work of ancient astronomers.

Solar Time Shift

The phenomenon caused by the Sun's ecliptic motion, resulting in a later sunrise each day.

North Star

Polaris, the star located near the North Celestial Pole, crucial for navigation.

Astronomical Knowledge

Information regarding celestial phenomena gathered over centuries, notably preserved by Arab scholars.

Philosophical Arguments

Rational justifications used by ancient astronomers to support their models of the universe.

Phase of Venus

Galileo observed that Venus undergoes a cycle of phases, similar to the Moon.

Galilean Moons

The four largest moons of Jupiter discovered by Galileo.

Naked-eye Observations

Astronomical observations made without the aid of telescopes or other instruments.

Ecliptic Tilt

The angle of 23.5° between the ecliptic and the celestial equator.

Ptolemaic Model

An ancient geocentric model that accounted for observed planetary motions using epicycles.

Celestial Navigation

Using the stars and celestial bodies to determine location and direction while traveling.

Astrological Zodiac

The twelve divisions of the celestial sphere utilized in astrology.

Aristotle

An ancient Greek philosopher who supported the geocentric model of the universe.

Earth's Rotation

The spinning of the Earth on its axis, causing daily apparent movement of the sky.

Earth's Orbit

The path Earth takes around the Sun, resulting in seasonal changes.

Astronomical Observations

The systematic study of celestial objects and their movements.

Mythology in Astronomy

The cultural narratives that associate constellations with stories and characters.

Galileo's Telescope

An optical instrument used by Galileo to make significant astronomical discoveries.

International Astronomical Union

The organization that officially named 88 constellations in the early 20th century.

Polaris' Altitude

The altitude of the North Star directly correlates to the observer's latitude.

Spherical Earth

The ancient Greeks' conclusion that the Earth is round based on observations.

Complex Epicycles

The circular orbits within orbits used in Ptolemy's geocentric model to account for retrograde motion.

Scientific Method

A systematic observation and experimentation approach, exemplified by Galileo.

Venus' Phases

The various shapes Venus appears to take due to its orbit around the Sun.

Fixed vs. Wandering Stars

The distinction made by ancient astronomers between stable constellations and moving planets.