Isochrone fitting of Galactic globular clusters -- III. NGC\,288,
  NGC\,362, and NGC\,6218 (M12)
  We present new isochrone fits to colour-magnitude diagrams of the Galactic
globular clusters NGC\,288, NGC\,362, and NGC\,6218 (M12). We utilize a lot of
photometric bands from the ultraviolet to mid-infrared by use of data from the
{\it HST}, {\it Gaia}, unWISE, Pan-STARRS, and other photometric sources. In
our isochrone fitting we use theoretical models and isochrones from the
Dartmouth Stellar Evolution Program and Bag of Stellar Tracks and Isochrones
for $\alpha$-enhanced abundance [$\alpha$/Fe]$=+0.40$, different helium
abundances, and a metallicity of about [Fe/H]$=-1.3$ adopted from the
literature. We derive the most probable distances $8.96\pm0.05$, $8.98\pm0.06$,
and $5.04\pm0.05$ kpc, ages $13.5\pm1.1$, $11.0\pm0.6$, and $13.8\pm1.1$ Gyr,
extinctions $A_\mathrm{V}=0.08\pm0.03$, $0.11\pm0.04$, and $0.63\pm0.03$ mag,
and reddenings $E(B-V)=0.014\pm0.010$, $0.028\pm0.011$, and $0.189\pm0.010$ mag
for NGC\,288, NGC\,362, and NGC\,6218, respectively. The distance estimates
from the different models are consistent, while those of age, extinction, and
reddening are not. The uncertainties of age, extinction, and reddening are
dominated by some intrinsic systematic differences between the models. However,
the models agree in their relative age estimates: NGC\,362 is $2.6\pm0.5$ Gyr
younger than NGC\,288 and $2.8\pm0.5$ Gyr younger than NGC\,6218, confirming
age as the second parameter for these clusters. We provide reliable lists of
the cluster members and precise cluster proper motions from the {\it Gaia}
Early Data Release 3.
