Lucianne Walkowicz: Finding planets around other stars. From Eric Weisstein's World of Astronomy. Winter_solstice_pivato.jpg (JPEG Image, 1280 × 554 pixels) Equinoxes & solstices. Ecliptic and celestial equator | Equinoxes | Solstices The ecliptic, celestial poles and celestial equator During the course of a year the Earth completes one orbit around the Sun.
To us on Earth we see this as the Sun moving against the background of stars through the year, along an imaginary line which we call the ecliptic. This defines the plane in which the Earth and most of the other planets orbit around the Sun.