  Visual and ultraviolet spatially resolved (~ 0."1) spectra of SN 1987A
obtained on days 3715 and 3743 with the Space Telescope Imaging Spectrograph on
the Hubble Space Telescope show that the high-velocity SN debris is colliding
with circumstellar gas. Very broad Ly-alpha emission with velocities extending
to ~ +/- 20,000 km/s originates inside the inner circumstellar ring and appears
to fill most of the surface area within 0."67 +/- 0."03 (0.14 pc at a distance
of 50 kpc) of the ring's center. The observed Ly-alpha flux from the shocked
ejecta is (1.85 +/- 0.53) 10^{-13} erg/cm2/s and (1.25 +/- 0.51) 10^{-12}
erg/cm2/s after correcting for extinction. A spatially unresolved blue-shifted
emission feature was discovered in H-alpha (and other lines) on the inner ring
at p.a. 31 +/- 8 degree. The H-alpha emission extends to -250 km/s with no
corresponding red-shifted emission. This highly localized interaction appears
to be the initial contact of the supernova blast wave with an inward protrusion
of the inner ring. The broad Ly-alpha emission and the `hot spot' are separate
interaction phemonena associated with the reverse and forward shocks,
respectively. We also find that the size of the inner ring in forbidden lines
of oxygen has a dependence on ionization potential, in agreement with
photoionization models of the ring.
