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TURBULENCE
The most common of all aberrations. Due to the nature of our atmosphere our telescopes have to look through a layer of air-in-motion. That air-in-motion causes turbulence effects, also known as seeing. On good nights turbulence is minimal and stars show their airy-discs and diffractions rings easy. These are the nights to star-test and look at stars ! On those “twinkle, twinkle litlle star” nights, our skies move abundantly and star-testing will be useless. Viewing at lower powers can still be pleasant.
The left image shows the static effect of 0.1 wave RMS turbulence, on the right once more 0.1 wave RMS turbulence is depicted but now animated for a 6” telescope. Smaller telescopes will show more extreme and dynamic effects from turbulence whilst larger telescope will show slow changing patterns. |
Mars as seen through a perfect 6” refractor. On the left without any turbulence and on the right with 0.1 wave RMS turbulence