The material was recorded in the H-alpha band, which is why the image differs from what can be obtained when observing the Sun in white light. The structures of the chromosphere and the prominences extending beyond the edge of the disk are particularly well visible.
The Moon obscured structures located above the Sun’s surface
It is worth noting the part of the recording in which irregular plasma structures are visible at the edge of the Sun. As the Moon’s disk moves, they are successively covered and disappear from the image.
These are prominences, areas of relatively cool and dense plasma held above the Sun’s surface by its magnetic field. They can extend tens of thousands of kilometres above the photosphere and, in the largest cases, even hundreds of thousands of kilometres.
During an eclipse, the geometry of the phenomenon makes it possible to observe the moment when the sharp edge of the Moon’s disk cuts across successive parts of the chromosphere. Our natural satellite is then positioned along the line between the observer and the Sun, obscuring also the matter extending beyond its visible edge.
We recorded the eclipse in the H-alpha band
H-alpha is a spectral line of hydrogen with a wavelength of approximately 656.28 nanometres, located in the red part of the visible light spectrum. Solar observations use very narrow filters that transmit light precisely near this wavelength.
This makes it possible to significantly reduce light originating from the photosphere and reveal structures associated primarily with the Sun’s chromosphere. In the H-alpha band, it is possible to record, among other things, prominences, filaments, active regions, and dynamic changes occurring in the plasma.
A prominence observed beyond the edge of the disk appears as a bright structure against the dark sky. The same matter viewed against the solar disk may take the form of a dark filament because it absorbs some of the H-alpha radiation coming from the lower layers of the Sun’s atmosphere.
The eclipse shows the difference between the photosphere and the chromosphere
In a conventional observation through a white-light filter, what is visible primarily is the photosphere, the layer responsible for most of the light reaching Earth. One can then observe, among other things, sunspots and granulation, provided that the instrument’s resolution and atmospheric conditions permit it.
H-alpha observation reveals a different layer of the Sun’s atmosphere. As a result, during a partial eclipse it is possible to follow not only the changing shape of the disk itself, but also the moment when structures located above the photosphere are obscured.
In the recording from Poznań on 12 August 2026, the edge of the Moon’s disk gradually reaches the prominences visible near the limb and then covers them. The recorded material therefore directly shows that the structures observed in H-alpha are not part of the surface visible in white light, but extend above it in the solar atmosphere.