Chapter 2: Stars and Constellations

Constellations

groups of stars

Magnitude Scale

A logarithmic scale used to measure the brightness of celestial objects. Lower numbers indicate brighter objects, with each step representing a 2.5-fold change in brightness. First magnitude being the brightest and sixth magnitude being the faintest

Zenith

the point of the celestial sphere directly above your head.

Nadir

the point of the celestial sphere directly under your feet

Ecliptic

the apparent path of the Sun against the background of stars

North and South Celestial Pole

located directly above Earth’s north and south poles

Circumpolar Circle

A circle in the sky parallel to the celestial equator, where certain stars never set and are visible all night from a specific location.

Precession

the gradual change in the orientation of Earth's axis of rotation, causing the position of the celestial poles to shift over time.

Rotation

the turning of a body on its axis

Revolution

the motion of a body around a point outside the body

Celestial Equator

Imaginary line in the sky directly above Earth's equator. Divides the celestial sphere into northern and southern hemispheres.