Scintillation (astronomy)
Under scintillation ( lat. Scintillare , glitter 'flicker') is understood in the astronomy an apparently changing brightness of a star , by light refraction in the earth's atmosphere caused. With particularly bright stars, dancing and colored sparkles can also emerge.
Emergence
This rapid and apparent change in brightness is caused by the fact that the refractive index of the atmosphere changes slightly locally due to air turbulence and the light from the star is thereby slightly deflected. This effect is comparable to the fact that the bottom of a swimming pool is not evenly illuminated by the sun due to the waves on the surface.
An important prerequisite for this effect is that stars are point-shaped objects even in large telescopes. The sun , moon and the planets do not show any scintillations, since they are also recognizable on earth as extended objects and the fluctuations are therefore averaged out over the extension of the object . However, even with the latter objects, the effect achieves a lower image sharpness than would be technically possible (i.e. from the optics, the film material or the resolution of the CCD sensor used ).
Determination and avoidance
When taking a photo or other long-term measurements on stars, the scintillation becomes noticeable due to the exposure time in that the star appears larger than it actually is due to its constantly changing position on the recording. This effect is called seeing in astronomy . In the case of flat objects, the photographic effect leads to a blurred image, visually the object appears to "wobble".
One possibility to compensate for the scintillation is the use of active or adaptive optics , as has been possible for some time with mirror telescopes . Another possibility is to build the telescopes in places with very calm air and / or in high mountain regions, as done by the European Southern Observatory . You can avoid atmospheric effects from the outset by placing the telescope in a vacuum. Probably the best known example of this is the Hubble space telescope .
Digital image processing can also reduce image disturbances caused by scintillation by superimposing and digitally sharpening numerous individual images, each with a very short exposure time, for example from a digital video camera. Unusable images are automatically sorted out by the software and the usable individual images are combined into a detailed final image.
The interference can also be calculated out by analyzing two light frequency ranges that are close together and that experience slightly different refraction.
Individual evidence
- ^ Description of the Giotto software
- ↑ http://imk-msa.fzk.de/Publications/Theses/MarionSchroedter/node5.html
Web links
- Hans Schremmer: Scintillation. November 17, 2007, accessed February 12, 2008 .