David Cass and Karl Shell coined the term sunspots as a suggestive and less technical way of saying "extrinsic random variable".
[1] The idea that arbitrary changes in expectations might influence the economy, even if they bear no relation to fundamentals, is controversial but has been widespread in many areas of economics.
[7] The name is a whimsical reference to 19th-century economist William Stanley Jevons, who attempted to correlate business cycle patterns with sunspot counts (on the actual sun) on the grounds that they might cause variations in weather and thus agricultural output.
In modern economics, the term does not indicate any relationship with solar phenomena, and is instead used to describe random variables that have no impact on the preferences, allocations, or production technology of a general equilibrium model.
The modern theory suggests that such a nonfundamental variable might have an effect on equilibrium outcomes if it influences expectations.
The Cass Shell example relies on the fact that general equilibrium models often possess multiple equilibria.
The idea was extended by Roger Farmer and Michael Woodford to a class of autoregressive models[14][15] and forms the basis for the Indeterminacy School in Macroeconomics.