Day & Night is a cellular automaton

Cellular automaton

A cellular automaton is a discrete model studied in computability theory, mathematics, physics, complexity science, theoretical biology and microstructure modeling. It consists of a regular grid of cells, each in one of a finite number of states, such as "On" and "Off"...

 rule in the same family

Life-like cellular automaton

A cellular automaton is Life-like if it meets the following criteria:* The array of cells of the automaton has two dimensions....

 as Game of Life

Conway's Game of Life

The Game of Life, also known simply as Life, is a cellular automaton devised by the British mathematician John Horton Conway in 1970....

. It is defined by rule notation B3678/S34678, meaning that a dead cell becomes live (is born) if it has 3, 6, 7, or 8 live neighbors, and a live cell remains alive (survives) if it has 3, 4, 6, 7, or 8 live neighbors, out of the eight neighbors in the Moore neighborhood

Moore neighborhood

In cellular automata, the Moore neighborhood comprises the eight cells surrounding a central cell on a two-dimensional square lattice. The neighborhood is named after Edward F. Moore, a pioneer of cellular automata theory. It is one of the two most commonly used neighborhood types, the other one...

. It was invented and named by Nathan Thompson in 1997, and investigated extensively by David I. Bell. The rule is given the name "Day & Night" because its on and off states are symmetric: if all the cells in the Universe are inverted, the future states are the inversions of the future states of the original pattern. A pattern in which the entire universe consists of off cells except for finitely many on cells can equivalently be represented by a pattern in which the whole universe is covered in on cells except for finitely many off cells.

Although the detailed evolution of this cellular automaton is very different from Conway's Game of Life, it exhibits complex behavior similar to that rule: there are many known small oscillators and spaceships, and guns formed by combining oscillators in such a way that they periodically emit spaceships of various types.