Sundial

A horizontal sundial laid out for Bushwick's latitude, 40.68° north, seen from above. The gnomon's sloping edge points at the celestial pole, and each hour line sits where tan θ = sin 40.68° × tan(hour angle), so the lines crowd together around noon and spread apart toward morning and evening. The shadow falls from where the sun really is right now. A sundial keeps sun time, which drifts away from the clock and back again over the year.