The word equilux in relation to the astronomical calendar is surprisingly new, used by experts since around 2006 and occasionally brought into the public eye via seasonal pieces in mainstream media. It is of course modelled on the earlier term equinox, which dates back to 1400 as a description of the point at which the sun crosses the equator. Both terms are derived from Latin, from aequus, meaning ‘equal’, plus nox (night) and lux (light) respectively.