The beacon is a common period-2 oscillator composed of two diagonally touching blocks. It was found by John Conway in March 1970.
The beacon is the simplest on-off. Its rotor, known as diagonal on-off, can be supported by several different stators: the next smallest is seen in eater plug. It can, in some sense, be considered a billiard table.
The beacon is the third most common oscillator in Achim Flammenkamp's census (after the blinker and toad). It is also the thirteenth most common object on Adam P. Goucher's Catagolue. In D2 diagonal symmetry, it is the eighth most common object, being more common than the tub but less common than the ship.
Beacons are significantly more common in diagonal symmetry than asymmetrically, so they can reform when hit, such as in the p26 pre-pulsar shuttle. The p24 shuttle, also having diagonal symmetry, contains a beacon, although this is incidental and not a catalyst.
A beacon can perform a snake-type catalysis in one of its two phases. Specifically, in the last generation before triggering the boat-bit reaction, the beacon is in the dense phase.
In other rules
tlife and its related rules have the transition S4q, making beacon an 8-cell still life systematically named "block-tie".
- 6P2.2 at Heinrich Koenig's Game of Life Object Catalogs