  The correlation of light from two sources leads to an interference pattern if
they belong to a specific time interval known as the coherence time, denoted as
$\Delta \tau$. The relationship governing this phenomenon is $\Delta \tau
\Delta \nu \approx 1$, where $\Delta \nu$ represents the bandwidth of the
light. This requirement is not satisfied, and hence, interference fringes are
not observable in the case of ordinary (thermal) light. In the 1950s, Robert
Hanbury Brown and Richard Q. Twiss explored interference phenomena using a
narrow bandwidth of thermal light. This investigation led to the discovery of
the Hanbury-Brown and Twiss effect (or the HBT effect in short), which has
since found applications in various fields, particularly stellar observations
and quantum optics. This article briefly traces the history of the HBT effect
and its applications in various fields, including stellar observations. More
importantly, it outlines the basic theoretical framework of this effect,
followed by the design and results of the correlation in intensity fluctuation
of a pseudo-thermal light in a college laboratory setting (Michelson
interferometer).
