  (Abridged) Far ultraviolet to far infrared images of the nearby galaxy
NGC5194, from Spitzer, GALEX, Hubble Space Telescope and ground--based data,
are used to investigate local and global star formation, and the impact of dust
extinction in HII-emitting knots. In the IR/UV-UV color plane, the NGC5194 HII
knots show the same trend observed for normal star-forming galaxies, having a
much larger dispersion than starburst galaxies. We identify the dispersion as
due to the UV emission predominantly tracing the evolved, non-ionizing stellar
population, up to ages 50-100 Myr. While in starbursts the UV light traces the
current SFR, in NGC5194 it traces a combination of current and recent-past SFR.
Unlike the UV emission, the monochromatic 24 micron luminosity is an accurate
local SFR tracer for the HII knots in NGC5194; this suggests that the 24 micron
emission carriers are mainly heated by the young, ionizing stars. However,
preliminary results show that the ratio of the 24 micron emission to the SFR
varies by a factor of a few from galaxy to galaxy. While also correlated with
star formation, the 8 micron emission is not directly proportional to the
number of ionizing photons. This confirms earlier suggestions that the carriers
of the 8 micron emission are heated by more than one mechanism.
