Introductory Astronomy: Sky Motion, Celestial Coordinates, and Seasons

Vocabulary flashcards covering fundamental astronomical concepts including celestial coordinates, sky motion, constellations, and the Earth's axial tilt.

Local Solar Time

A system of timekeeping based on the position of the sun in the sky, where time events like sunrise, noon, and sunset are determined by solar position.

Noon

The time of day when the sun reaches its peak height and maximum elevation in the sky.

Equinox

One of two days in the year when daytime lasts exactly twelve hours, occurring between winter and summer (spring equinox) and summer and winter (fall equinox).

Constellations

An official set of sky regions with boundaries established by international agreement through the International Astronomical Commission, used as rough landmarks.

Celestial Sphere

An imaginary dome or sphere centered on the observer or Earth, used to map the two-dimensional positions of astronomical objects.

North and South Celestial Poles

The points on the celestial sphere located directly overhead the Earth's North and South Poles, around which the sky appears to rotate daily.

Celestial Equator

The extension of the Earth's equator out onto the celestial sphere, located $90^\circ$ away from the celestial poles.

Zodiac Constellations

The set of constellations located along the ecliptic through which the sun appears to travel over the course of a year.

Altitude

The angle measured between $0^\circ$ at the horizon and $90^\circ$ straight overhead that specifies an object's elevation in the sky.

Zenith

The point on the celestial sphere directly overhead an observer, corresponding to an altitude of $90^\circ$.

Direction (Azimuth)

An angular measurement specified using cardinal directions or degrees relative to north used alongside altitude to pinpoint objects in the sky.

Polaris

The North Star located very close to the north celestial pole, forming the tail star of the Little Dipper and pointed to by the outer bowl stars of the Big Dipper.

Southern Cross

A bright, distinctive constellation in the Southern Hemisphere used to locate the approximate direction of the south celestial pole.

Earth's Axial Tilt

The $23.5^\circ$ tilt of Earth's rotation axis relative to its orbital plane, which drives seasonal changes in sunlight intensity and duration across hemispheres.