H-alpha

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The sun as seen with an H-alpha telescope

In astronomy and physics, H-alpha or  Hα is the brightest spectral line of excited hydrogen (chemical symbol: H) in visible light. It lies in red light at a wavelength of 656.28  nanometers and is of particular importance for solar observation : special interference filters ( Fabry-Pérot interferometer ) only allow sunlight to pass through this area, which allows the exact structure of the uppermost solar layer ( chromosphere ) becomes visible with the sun flares and filaments .

Visible area of ​​the hydrogen spectrum with the lines Hα (right) to Hζ (left). Two lines on the left are no longer visible to the eye, but were recorded with UV-sensitive sensors

Since hydrogen is by far the most abundant chemical element in space , observations with H-alpha filters are instructive not only for stars , but also for gas nebulae and other celestial objects.

The Hα line is the brightest of a whole series of lines called the Balmer series after the person who discovered it ( Jakob Balmer , 1885). The other lines in this series are called Hβ, Hγ, etc., where Hβ lies in the green-blue light, Hγ in the blue-violet and Hδ at the violet edge of the visible spectrum . Further lines (Hε, Hζ, ...) already fall into the UV range and were only discovered later. The wavelengths of this radiation are emitted when an electron “jumps down” from a higher to the second lowest energy level in its orbit around the atomic nucleus . Conversely, they are absorbed (i.e. into dark lines) when an electron from incident light takes the energy it needs to transition to a higher energy level .

See also

Remarks

  1. ↑ The electron transitions from / to the lowest energy level of the hydrogen atom are called the Lyman series and are in the very short-wave UV (121 → 91 nm). The transitions from / to the third electron level ( Paschen series ), however, are in the near infrared .