  Eclipses are very favourable for the photosphere- chromosphere and corona
interface observation as the occultation takes place in space, free of
parasitic light coming from the occulting disk (the Moon). Independently, EUV
filtergrams of the limb region obtained in space were analyzed using one
dimensional hydrostatic VAL models but this method ignores the ubiquitous
magnetic field emergence phenomenon associated with the chromospheric network.
A jump of temperature from 0.01 to 1 MK is observed near the 2 Mm heights and
higher, further producing a permanent solar wind flow. The heating processes
responsible for this temperature jump and for the flow are not yet fully
understood. In this thesis, we reconsider these problems with new high cadence
CCD flash spectra, white light (W-L) eclipse images and new EUV images obtained
with space-borne instruments. We illustrate the mechanisms of low First
Ionisation Potential (FIP) emission lines present in the low layers of the
solar atmosphere, and nearby prominences. We characterize in detail the He
shells and the solar interface region.
  Main results: i) The solar edge and the temperature bifurcation:
structuration and discussion of the analysed low FIP lines and the true
continuum in the 400 to 600 km heights above the limb, emission mechanisms; ii)
Visible mesospheric and chromospheric emission lines in the interface regions
including the Paschen alpha HeII line starting at 800 km above the limb,
produced by photo-ionisation showing shells around the Sun and probing the
prominence-corona interface; iii) The contribution of small scale dynamical
spicules and macro-spicules starting at 1 Mm above the limb showing that the 1D
hydrostatic stratified models are not adapted to the upper layers.
