The equatorial sundial is a special case of the inclining dial, for which the layout of the hour lines becomes very simple. Indeed, this dial is placed in the plane of the celestial equator (prolongation of the terrestrial equator to infinity).

The style is perpendicular to the plane, and directed towards the celestial pole. The shadows are rectilinear and move oppositely to the sun, at the same speed. The hour lines are thus regularly spaced every 15° (360° / 24 h). The declination lines are circles.

This type of sundial is seasonal because when the sun is above the celestial equator, it lights the upper side of the dial, whereas during the rest of the year, it lights the lower side. Around the equinoxes, this dial is lit edge-on all day long, and it is quite impossible to read the hour on it.

It's the only dial which is really simple to design without any calculation.

Upper face of an equatorial sundial

Lower face of an equatorial sundial