  We present deep R and narrow-band Halpha images of Arp 78 obtained with the
WIYN 3.5-m telescope on Kitt Peak. GALEX observations had shown a very extended
UV structure for this system, reaching beyond the optical radius of Arp 78 and
also beyond its previously known Halpha-radius. Our new Halpha data now show
agreement not only with the spatial extent of the near- and far-UV maps, but
also in terms of structural details. Star formation rates derived from
L(Halpha) and L(FUV) are in reasonable agreement, indicating that in this case
the upper stellar IMF in the UV-bright outer arm is relatively normal. The star
forming sites in the outer arms are younger than ~15 Myr and massive enough to
properly sample the IMF up to high masses; their low optical visibility
evidently is a property of their youth.
