  In this work we have compiled 37,692 observations of 27 periodic and
non-periodic comets to create the secular light curves (SLCs), using 2 plots
per comet. The data has been reduced homogeneously. Our overriding goal is to
learn the properties of the ensemble of comets. More than 30 parameters are
listed, of which over ~20 are new and measured from the plots. We define two
ages for a comet using activity as a proxy, the photometric age P-AGE, and the
time-age, T-AGE. It is shown that these two parameters are robust, implying
that the input data can have significant errors but P-AGE and T-AGE come out
with small errors. This is due to their mathematical definition. It is shown
that P-AGE classifies comets by shape of their light curve. The value of this
Atlas is twofold: The SLCs not only show what we know, but also show what we do
not know, thus pointing the way to meaningful observations. Besides their
scientific value, these plots are useful for planning observations. The SLCs
have not been modeled, and there is no cometary light curve standard model as
there is for some variable stars (i.e. eclipsing binaries). Comets are
classified by age and size. In this way it is found that
29P/Schwassmann-Wachmann 1 is a baby goliath comet, while C/1983 J1
Sugano-Saigusa-Fujikawa is a middle age dwarf. There are new classes of comets
based on their photometric properties. The secular light curves presented in
this Atlas exhibit complexity beyond current understanding.
