Abstract: The present invention provides an apparatus and method for measuring the temperature of a moving radiant object. A probe, such as a pyrometer, is disposed in an opening of a vacuum chamber adjacent a radiation transparent window. The probe defines an optical path which intercepts the radiant object entering or exiting a processing chamber. The radiant object is moved through the optical path and emits electromagnetic waves. The electromagnetic waves are collected by the probe and transmitted to a signal processing unit where the waves are detected and converted to a temperature reading. If desired, the accumulated data may then be used to generate a cooling curve representing the thermal effects experienced by the radiant object. Extrapolation or correlation methods may be used to extend the cooling curve to points in time prior to or after the data collected by the probe.