Foundations · Overview
This section introduces the basic concepts used to describe the sky: the celestial sphere and coordinate systems, time systems, star charts and constellations, the apparent motion of celestial bodies, and the magnitude system. It is the starting point of the learning path and provides the foundation for the later material on observing and astrophotography.
What this section covers
Section titled “What this section covers” The Celestial Sphere and Coordinate Systems The celestial sphere and the equatorial, horizontal, ecliptic, and galactic systems, with conversions between them.
Time Systems Sidereal and solar time, UT/UTC and leap seconds, the Julian Date, and how to predict transits.
Star Charts and Constellations The 88 IAU constellations, the Chinese asterism system, star designations, and star-hopping.
Apparent Motion of Celestial Bodies Diurnal and annual motion, planetary retrograde, plus precession, nutation, parallax, and proper motion.
The Magnitude System Apparent and absolute magnitude, distance modulus, color index, and surface brightness in practice.