Expert: Tom Whiting - 1/2/2008

Question
We observe stars to scintillate through our naked eye (aperture about 5mm).
I recorded Sirius with a common video camera (aperture about 25mm), and
this video record clearly shows the intensity variations. The record of Mars,
taken within a minute before that of Sirius, shows a very smooth non-
varying intensity.

My questions are "Does scintillation become less noticeable in stars as the
size of the aperture of the telescope increases?" and "If so, what is the
aperture size at which scintillation becomes just marginally detectable?"

Answer
Hi Martin,
No.  Scintillation is not dependent on aperture....the
same "guy" (jet stream, moisture, dust, etc) is still swimming at the top of our "atmosphere" swimming pool.  Your difference is....planets are not subject to as much scintillation as stars because stars are actually pin-points coming in (one single row of photons, like 0.001 arc-second), whereas planets are in reality small disks (thicker shafts of light) coming down to us.  So you have an unfair comparison there. Mars' diameter is currently about 15 arc-seconds. So starlight is much more
susceptible to a wavering atmosphere than a thicker light shaft of a planet.  (That's what you've "proved" here.)

A better comparison....how much DETAIL did you see on
the surface of Mars...polar caps, Syrtis Major, individual
craters, canyons, etc?
Now the resolution comparison is the same as a pin-point star.  (The name of the "game" is...resolution.)
And with Sirius wildly twinkling, I'll bet Mars is just
an orange-yellow blob, with no surface detail at all.
That's why astronomers have developed more modern telescopes with what is called "adaptive optics" where they can microscopically bend the mirror surface to counteract atmospheric turbulence and thus obtain higher resolution through our atmosphere.  It incorporates a laser
beam shot into the sky close to their target with a scope
observing the end of the beam, and a computer to measure the atmospheric fluctuations of the laser, then the computer instructs the equivalent of suction cups on the main mirror to apply just the right pressure (or partial vacuum) to adjust the mirror accordingly, to present a clearer picture of the object being imaged.
Hope all this helps,
Clear Skies,
Tom Whiting
Erie, PA