Observing the Stars and Planets: Clockwork of the Universe

Ecliptic Plane The plane within which lies the Earth’s orbit around the Sun. Zodiac The 12 constellations on the celestial sphere which are intersected by the ecliptic plane. Year⊕ The time that it takes for the Earth to complete one full revolution (i.e. orbit) around the Sun such that the Sun is in the same direction with respect to the fixed stars. This is referred to as a solar year, which at the moment is equal to 365.256 Earth solar days. Equinoxes The direction of the Sun (as seen from Earth) at the 2 points in the Earth’s orbit when the Sun passes through the zenith for an observer on the equator. Solstices The direction of the Sun (as seen from Earth) at the 2 points in the Earth’s orbit when the Sun passes through the zenith for an observer at Lat = +23.5° and at Lat = -23.5°.