A system for operating a gas turbine includes a compressor, a combustor, and a turbine. The combustor and turbine define a hot gas path. A sensor disposed outside the hot gas path measures internal thermal emissions from the combustor or turbine and generates a first signal reflective of the internal thermal emissions. The internal thermal emissions are infrared or ultraviolet emissions. A controller connected to the sensor receives the first signal and adjusts the compressor, combustor, or turbine in response to the first signal from the sensor. A method for operating a gas turbine includes measuring internal thermal emissions from inside a combustor or turbine using a sensor disposed outside the hot gas path. The method further includes generating a first signal reflective of the internal thermal emissions and adjusting the operation of the compressor, combustor, or turbine in response to the first signal from the sensor.