Pollution from bright city lights makes it nearly impossible to stargaze within a city setting. The supply and demand for electricity used in city lighting are shown in the graph. Suppose the marginal external cost for an additional kilowatt hour (kWh) of electricity is 5 cents. Drag the endpoints of the blue line to draw in the marginal social cost (MSC) curve for electricity. Place the black dot at the point corresponding to the socially optimal quantity and price for electricity. Assume the government places an optimal Pigouvian tax on electricity used at night to reduce light pollution so that people can enjoy the stars. As a result of the Pigouvian tax, Price, marginal social cost of electricity (cents/kWh) 50 40 30 20 10 MSC of Light Pollution Quantity of electricity (kWh)