Although the contribution of a chromosphere to the total flux may be
small, it plays a vital role as the interface between the star and interstellar space, as
it is where the stellar wind originates. The very outermost layers of a star are expected
to be turbulent. Images of the solar chromosphere and corona reveal both small-scale
inhomogeneities (prominences and spaces) and large-scale variability (polar plumes near
sunspot minima, streamers near sunspot maxima), and something similar but more exaggerated
can be expected in cool supergiants. Samplings of the high chromosphere in late-K
supergiants show extreme variability in both density and velocity, and can be thought of
as analogues of the solar case. Series of chromospheric-eclipse spectra of the Ca ii
K line in 31 Cyg, 32 Cyg and ζAur demonstrate (a) the presence in
the high chromosphere of discrete, rapidly-moving clumps of gas, (b) that structures are
not stable or symmetrical, either from eclipse to eclipse or from ingress to egress in the
same eclipse, (c) plenty of empty space, and (d) huge differences between one late-K
supergiant and another. What information can this evidence offer as regards the outer
structure and wind of Betelgeuse?