  We present the first extensive photometric results of CL Aur from our BVRI
CCD photometry made on 22 nights from 2003 November through 2005 February.
Fifteen new timings of minimum light were obtained. During the past 104 years,
the orbital period has varied due to a periodic oscillation superposed on a
continuous period increase. The period and semi-amplitude of the oscillation
are about 21.6 yrs and 0.0133 d, respectively. This detail is interpreted as a
light-travel-time effect due to a low-luminosity K-type star gravitationally
bound to the CL Aur close system. Our photometric study indicates that CL Aur
is a relatively short-period Algol-type binary with values of q=0.602 and
i=88$^\circ$.2. Mass transfer from the secondary to the primary eclipsing
component is at least partly responsible for the observed secular period change
with a rate of dP/dt = +1.4$\times10^{-7}$ d yr$^{-1}$. A cool spot model has
been calculated but we think that an alternative hot-spot model resulting from
a gas stream impact on the hot star is more reasonable despite two difficulties
with the explanation. Absolute dimensions of the eclipsing system are deduced
and its present state is compared with tracks for single star and conservative
close binary evolution. Finally, we examine the possible reconciliation of two
different calculations of the luminosity of the hot spot and a
re-interpretation of the secular term of the period variability.
