  Sparse and serendipitous asteroid photometry obtained by wide field surveys
such as the Asteroid Terrestrial-impact Last Alert System (\ATLAS) is a
valuable resource for studying the properties of large numbers of small Solar
System bodies. We have gathered a large database of \ATLAS photometry in
wideband optical cyan and orange filters, consisting of 9.6\e{7} observations
of 4.5\e{5} main belt asteroids and Jupiter Trojans. We conduct a phase curve
analysis of these asteroids considering each apparition separately, allowing us
to accurately reject outlying observations and to remove apparitions and
asteroids not suitable for phase curve determination. We obtain a dataset of
absolute magnitudes and phase parameters for over 100,000 selected asteroids
observed by \ATLAS, $\sim66,000$ of which had sufficient measurements to derive
colours in the \ATLAS filters. To demonstrate the power of our dataset we
consider the properties of the Nysa-Polana complex, for which the \ATLAS
colours and phase parameters trace the S-like and C-like compositions amongst
family members. We also compare the properties of the leading and trailing
groups of Jupiter Trojans, finding no significant differences in their phase
parameters or colours as measured by \ATLAS, supporting the consensus that
these groups were captured from a common source population during planetary
migration. Furthermore, we identify $\sim9000$ asteroids that exhibit large
shifts in derived absolute magnitude between apparitions, indicating that these
objects have both elongated shapes and spin axes with obliquity $\sim 90$
degrees.
