Sterrentwinkeling

Sterrentwinkeling is the Dutch term for stellar scintillation, the rapid, small-scale fluctuations in the observed brightness and apparent position of stars when viewed from the Earth's surface. These fluctuations are caused by turbulence in the Earth's atmosphere, which produces time-varying refractive index along the light's path. Because stars are effectively point-like sources, their light is refracted by many turbulent cells in the air, causing interference that leads to twinkling.

Temperature and humidity variations in atmospheric layers create refractive-index inhomogeneities. As these cells move with wind, the optical path changes on timescales from milliseconds to seconds, producing brightness variations and tiny shifts in the image centroid. Shorter wavelengths show somewhat stronger scintillation, a chromatic effect, and the overall amplitude increases when the line of sight passes through more air (lower altitude or higher airmass).

Observational impact: Stellar twinkling adds noise to ground-based photometry and can affect precise astrometry. Planets and other extended sources tend to twinkle less because their light is spread over a disk, smoothing fluctuations. The effect decreases with larger telescope apertures because the light is averaged over a bigger area. It is most pronounced for bright, high-contrast stars and near the horizon.

Mitigation and use: Observers mitigate by observing at the highest possible elevation, using longer exposure times or beam-averaging, and employing space-based telescopes. Adaptive optics mainly corrects wavefront distortions and blur rather than scintillation, though high-speed AO and fast detectors can reduce some impact. Scintillation itself can be used as a diagnostic tool to study atmospheric turbulence.