These are prominences, that is, relatively cool and dense regions of plasma held in the solar atmosphere by the magnetic field. Their sizes can reach tens of thousands of kilometers, and the largest structures of this type extend for hundreds of thousands of kilometers.
As the Moon moves, successive parts of the prominences disappear from view. The geometry of the eclipse means that our natural satellite obscures not only the photosphere, but also matter located above its visible edge if, from the observer's point of view, it lies along the same line of sight.
This is precisely why H-alpha observations make it possible to follow the occultation of structures that are not visible at all during a typical white-light observation of the Sun.
We recorded the solar eclipse in the H-alpha band
H-alpha is a spectral line of hydrogen with a wavelength of approximately 656.28 nanometers, located in the red part of the visible-light spectrum. Solar observations use special filters with a very narrow transmission band, allowing radiation through in the immediate vicinity of this wavelength.
Such filtering makes it possible to significantly reduce the dominant light of the photosphere and reveal structures associated with the Sun's chromosphere. An H-alpha image can show, among other things, prominences, filaments, active regions, and changes occurring in plasma under the influence of the solar magnetic field.
A prominence located beyond the edge of the solar disk is visible as a bright structure against the dark sky. The same matter viewed against the solar disk may appear as a dark filament because it absorbs some of the H-alpha radiation coming from lower layers of the Sun's atmosphere.
As a result, footage of a partial eclipse simultaneously shows the motion of the Moon's disk and the structure of the solar chromosphere, which remains virtually invisible in an ordinary photospheric image.
The photosphere and chromosphere during a single eclipse
In observations made through an appropriate white-light filter, we see primarily the photosphere, the layer responsible for most of the visible radiation reaching us from the Sun. With suitable aperture, resolution, and atmospheric conditions, it is possible to record sunspots and granulation, among other features.
An H-alpha image shows different structures. It is dominated by phenomena associated with the chromosphere and matter held by the magnetic field above the photosphere. A partial eclipse provides a rare opportunity to observe them against the very distinct boundary defined by the edge of the Moon.
In footage recorded on August 12, 2026, in Poznań, the edge of the lunar disk gradually approaches the prominences visible near the Sun's limb and then successively obscures them. The material therefore makes it possible to directly see that the structures recorded in the H-alpha band do not lie on the surface of the photosphere, but extend high above it in the solar atmosphere.