mercoledì, febbraio 20, 2008

Simulation of bad seeing

This video shows another realistic simulation of a star image seen with a telescope under very bad seeing conditions. I do not know the exact value of the turbulence scale (the Fried's parameter), but, judging the number nd size of speckles, it can be estimated to be one tenth or less than the scope diameter.
The step between frames correspond to a lateral displacemnt of the wavefront which amounts to 1% of the scope diameter (e.g. for 1 meter and wind speed of 10 m/s it is 1 cm and 1 ms). If played at 25 fps, the movie is ~40 times slower than reality.
An interesting aspect is the way the single speckles change. They both move and vary in intensities, but the latter is quicker. The speckle pattern looks more like swarm of bubbles appearing and fading than a moving set of spots. Is that true or an artifact? Here is a slow motion movie of Eps aql.