Success! However, it's not over til it's over...
Greetings again from historic Mount Wilson Observatory, perched in the Angeles National Forest mountains, above Los Angeles. As previously mentioned, we're here using the Center for High Angular Resolution Astronomy (CHARA) telescope array of 6 one-meter telescopes, operated by Georgia State University. The light from 4 of these telescopes at a time can be merged in the Michigan IR Combiner, or MIRC. Each pair of telescopes is capable of producing interference fringes. Measuring the fringe contrast and knowing the wavelength and telescope separation for each pair over the course of an evening, provides pieces of information that can be used to construct an image.
How is that done? Let me try an analogy: each piece of info from this process is something like getting a puzzle piece from a jigsaw puzzle. With patience, during a 3 night observing run, you may be able to collect tens of pieces. However, that handful of pieces happens to be part of a 1,000 piece puzzle. Your problem is to try to figure out what the picture looks like based on this "sparse sampling" of the full image - a bit like guessing the phrase on "Wheel of Fortune" when only the first few letters are revealed. My thanks to PJ for suggesting this puzzle piece analogy.
Fortunately with computer assistance, we can use mathematical methods to interpolate and reconstruct the full image, although the process has its limits. Using CHARA+MIRC, we can measure picture elements on the 0.5 milli-arcsecond scale, which is about 10x finer resolution than Hubble Space Telescope (7 milli-arcsec). A milli-arcsecond is 1/1000 part of a full arcsecond, or a nano-radian angle. This is like looking at details on a small coin at a distance of 10,000 kilometers (about 6,000 miles).
What have we seen when we looked at 2.5 milli-arcsec wide epsilon Aurigae this week (mid-ingress, early Nov 2009)? The team is working the details, but it appears we do see the eclipse in progress - think "Pac Man" in terms of shape. In coming weeks, we hope to provide more details once the computer solutions are finalized. The significance of this result is severalfold: we can provide a direct test of the dark disk eclipser in the system and better characterize its shape and opacity. With a little luck and no more fires and rockslides around Mount Wilson, we hope to come back and get another snapshot to see the anticipated changes during the balance of 2009 as totality comes along. We still need you to get outside after dark and check out the brightness of epsilon Aurigae and report your results here at Citizen Sky. Thanks!