Motion of the Sun, Earth, Moon, and Planets

A set of flashcards covering key vocabulary from the lecture on the motion of the Sun, Earth, Moon, and planets.

Ecliptic

The apparent path the Sun follows through the sky over the course of a year.

Solar Day

The time it takes for Earth to complete one full rotation relative to the Sun, about 24 hours.

Sidereal Day

The period of one complete rotation of Earth relative to the stars, approximately 23 hours and 56 minutes.

Analemma

The figure-eight pattern traced by the position of the Sun at the same time each day over a year.

Precession

The slow, circular motion of Earth’s axis that changes the direction of its tilt over time.

Retrograde Motion

The apparent backward movement of a planet as observed from Earth due to differences in their orbital speeds.

Synodic Month

The time from one new Moon to the next, approximately 29.5 days.

Sidereal Month

The time it takes the Moon to make one complete orbit around Earth relative to the stars, about 27.3 days.

Lunar Eclipse

An event when the Moon passes through Earth’s shadow, visible only during a full Moon.

Solar Eclipse

An event when Earth passes through the shadow of the Moon, only possible during a new Moon.

Horizon

The line where the Earth’s surface and the sky appear to meet.

Tropics of Cancer and Capricorn

The latitudes where the Sun can be directly overhead at noon during the solstices.

Arctic Circle

The latitude above which the Sun does not set during the summer solstice and does not rise during the winter solstice.

Seasons

The four distinct periods (spring, summer, autumn, winter) caused by Earth's axial tilt and its orbit around the Sun.

Phases of the Moon

The different appearances of the Moon as it orbits Earth, resulting from the varying angles of sunlight.

Celestial Sphere

An imaginary sphere that encompasses the Earth, on which all celestial objects can be thought to reside.

Earth’s Axis

An imaginary line that runs through the North and South poles around which Earth rotates.

Ecliptic Plane

The plane of Earth's orbit around the Sun.