The Wires used in the thermocouples, as the name suggests, are extremely fine as thin as 0.005 inch.
These thermocouples are made of materials such as chromel and Constantan. The sensing tip measures the temperature which is the hot junction. The Thermocouple is connected to a measuring device. The reference temperature, which is the ambient temperature of the thermocouple is provided by another sensor such as a thermistor fitted inside the measuring device.
Fine Wire Thermocouples, due to their slender construction, are not affected by solar loading.