  We use Gaia Data Release 2 (DR2) to place 252 Herbig Ae/Be stars in the HR
diagram and investigate their characteristics and properties. For all known
Herbig Ae/Be stars with parallaxes in Gaia DR2, we collected their atmospheric
parameters and photometric and extinction values from the literature. To these
data we added near- and mid-infrared photometry, collected H$\alpha$ equivalent
widths and line profiles, and their binarity status. In addition, we developed
a photometric variability indicator from Gaia's DR2 information. We provide
masses, ages, luminosities, distances, variabilities and infrared excesses
homogeneously derived for the most complete sample of Herbig Ae/Be stars to
date. We find that high mass stars have a much smaller infrared excess and have
much lower optical variabilities compared to lower mass stars, with the break
at around 7M$_{\odot}$. H$\alpha$ emission is generally correlated with
infrared excess, with the correlation being stronger for infrared emission at
wavelengths tracing the hot dust closest to the star. The variability indicator
as developed by us shows that $\sim$25% of all Herbig Ae/Be stars are strongly
variable. We observe that the strongly variable objects display doubly peaked
H$\alpha$ line profiles, indicating an edge-on disk. The fraction of strongly
variable Herbig Ae stars is close to that found for A-type UX Ori stars. It had
been suggested that this variability is in most cases due to asymmetric dusty
disk structures seen edge-on. The observation here is in strong support of this
hypothesis. Finally, the difference in dust properties occurs at 7M$_{\odot}$,
while various properties traced at UV/optical wavelengths differ at
3M$_{\odot}$. The latter has been linked to different accretion mechanisms at
work whereas the differing infrared properties and variabilities are related to
different (dust-)disk dispersal mechanisms.
