  Total solar eclipse (TSE) coronal large and small scale events were reported
in the historical literature but a definite synoptic coverage was missing for
studying a relationship with the more general magnetic context of the
solar-disk. We here analyze temporal changes in the solar corona before,
during, and after the total solar eclipse on 21 August 2017 from a set of
ground-based and of space-borne observations. High-quality ground-based
white-light (W-L) observations and a deep image processing allow us to reveal
these changes for the first time with a fraction of a one-minute time
resolution. Displacements of a number of fine coronal features were measured
for the first time at these small radial distances, using a diffraction limited
instrument at a single site. The comparison with space-based observations,
including observations from the {\it Solar Terrestrial Relations Observatory}
(STEREO) mission, showed that the features belong to a slow coronal mass
ejection (CME) propagating through the corona with the nearly constant speed of
250 km/s. Our TSE images provide the same typical velocity as measured at a
distance of one solar radius from the surface. The event was initiated by
coronal dynamics manifested by a prominence eruption that started just before
the eclipse observations and an ascent of a U-shaped structure visible in the
AIA 171 A channel, which we assume as the lower part of a coronal cavity. The
prominence material was observed draining down towards the chromosphere along
the prominence arch. While the prominence disappears in the STEREO-A
field-of-view at the height of about 6$^{\prime}$ above the limb, the
corresponding flux rope seems to continue towards the outer corona and produces
the slow CME with turbulent motion. The overall mass of the moving features is
evaluated based on absolute photometrical data extracted from our best W-L
eclipse image.
