Sunspot

In economics, sunspots are extrinsic random variables upon which participants coordinate their decisions. Extrinsic random variables do not affect economic fundamentals directly, but may have an effect on equilibrium outcomes because they influence expectations. In a proper sunspot equilibrium, the allocation of resources depends on sunspots to a significant extent.

Sunspot models are rational-expectations and general-equilibrium models that explain excess volatility in a system.

Uncertainty about economic fundamentals, known as intrinsic uncertainty, is not the only source of volatility in economic outcomes. Market uncertainty can also be driven by extrinsic uncertainty, which includes such variables as market psychology, self-fulfilling prophecies and "animal spirits", collectively known as sunspots.

The concept of sunspot equilibrium was introduced by David Cass and Karl Shell in 1983, with the term 'sunspot' being something of a spoof on the work of the 19th-century economist Jevons, who related the business cycle to the cycle of actual sunspots. Shell notes that the best way to analyze bank runs and related financial-system weaknesses is as a sunspot-equilibrium outcome. The 2008 financial meltdown can be viewed as partly sunspot driven.