Charting the Heavens Pt.1

Vocabulary flashcards covering key astronomical concepts from the lecture notes.

Light-year

The distance light travels in one year (about 9.46 × 10^12 kilometers).

Astronomical Unit (AU)

Average distance from the Earth to the Sun (about 150 million kilometers).

Planet

A rocky or gaseous body that orbits a star; Earth is a planet.

Galaxy

A massive collection of billions of stars bound by gravity.

Milky Way

Our galaxy, a vast collection of stars including the Sun.

Universe

The totality of all space, time, matter, and energy.

Celestial Sphere

A conceptual two-dimensional surface representing how the sky looks from Earth.

Declination

Celestial latitude; north of the celestial equator is +, south is –.

Right Ascension

Celestial longitude used to locate objects in the sky; measured in hours.

Constellation

A recognized pattern of stars forming a figure.

Zodiac

The twelve constellations through which the Sun appears to move over a year.

Ecliptic

The Sun's apparent path on the celestial sphere, along which the zodiac lies.

Axial Tilt

The tilt of Earth's axis relative to its orbit around the Sun, about 23.5 degrees.

Seasons

Periods of the year with varying sunlight due to axial tilt, not distance.

Solstice

Summer solstice (June 21) and winter solstice (Dec 21); longest/shortest days.

Equinox

Vernal (Mar 21) and autumnal (Sept 21) equinoxes; roughly equal day and night.

Precession

Slow wobble of Earth's axis, completing a cycle about every 26,000 years; changes pole star.

Polaris

Current North Star, near the north celestial pole.

Vega

Bright star that will be a pole star around A.D. 14,000 due to precession.

Thuban

Pole star around 3000 B.C. due to precession.

Scientific Theory

A well-tested explanation of natural phenomena; testable and supported by evidence; can be revised but not proven with 100% certainty.

Seasonal Motion of the Night Sky

The apparent change in which constellations are visible over the year as Earth orbits the Sun.