Yes, Thank You Chris Peterson, you are excellently knowledgeable in the observational disciplines of astronomy !
(however much we may differ on the theoretical astrophysics side)
I was wondering if milli (as in m.a.s.) meant to multiply by 1000, it does !
As to the unevenness of the surface brightness of Betelgeuse, I believe it is 'an artifact', a result of the interferometer process that was used to produce the image, akin to digital photos at certain enlargements or angles will get a sideways lineyness to them, like polarization effects in a way.
http://www.space.com/scienceastronomy/a ... y_101.html
"In astronomy, we will be dealing with the interference of two light waves. If both waves are in step or in phase, that is, the crest of both waves coincide, the two will add together to form a single wave. This combined wave will have a higher crest and deeper trough (or larger amplitude). In the case of light waves, two dimmer light beams will add together to form a brighter beam -- this is called constructive interference.
"On the other hand, destructive interference occurs when the two waves are out of step with each other; that is, the crest of one coincides with the trough of the other. Here, although the waves are still adding together, they cancel each other out. So, the amount of interference that occurs depends on both the amplitudes of the two waves and the degree to which their respective crests and troughs are in phase with each other.
"What is looked for are alternating bands of light and dark, called fringes. Fringes are bright where the beams are constructively adding together and dark where they are canceling each other out.
"What makes the interferometer such a precise measuring instrument is that these fringes are only one light-wavelength apart. In visible light, about 590 nanometers --that corresponds to 1/43,000th of an inch! Any movement along the optical axis by either flat mirror will cause the fringes to shift an equal amount in lockstep. The measurement of this movement is made by literally counting the number of fringes - each dimming and brightening of light - one wavelength at a time!
"Such a precise system is also incredibly sensitive -- so much so that any vibration, movement, thermal expansion, etc. is picked up as well. In fact, Michelson's early experiments were affected by street traffic vibrations up to 1,000 feet away! Using shorter wavelengths of light allow greater precision, but are much more difficult to work with (the fringes are closer together).
"In astronomical interferometry, the most important parameter is the "baseline," the distance between the flat mirrors. Another key parameter is called "visibility,'' which is the difference in brightness between a fringe and the relative darkness between it and the next fringe.
"If one plots visibility versus baseline, the maximum visibility occurs at a baseline of zero, and decreases as baseline is increased. At some point, the visibility drops to zero (and the fringes disappear). This is called the "resolving point.'' At greater baselines, the fringes reappear and visibility increases, but only to about 10% of the peak visibility before dropping again. The heights of subsequent peaks taper off.
"The significance of the resolving point is that if you are observing a star, it gives a direct measurement of the apparent diameter of the object against the sky. If the distance to the star is known, then the actual diameter can be calculated. (By analogy, the apparent size of coin held up varies by the distance you hold the coin up from your eye.) Although stars are large, they are at very great distances, and so the apparent diameters are very small, typically a few thousandths of an arcsecond (1 milliarcsecond is about 275 billionths of a degree)."
- - -
And thusly I suspect that some of the variations in Betelgeuse's surface brightness are partly a result of the process used to obtain the image.
The Spotty Surface of Betelgeuse
