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Log, Feb 29, 2008

8 people. What could be better than a moonless night with highly stable seeing? Well for one thing it would be nice if the clouds stayed away more than two and a half hours. Needless to say, they didn't. We got hit about 8 or 8:15 by clouds which were the forerunners of Saturday's sleet and snow.

We tried theme and variations on an apodizing mask. Sirius was about as stable as we have seen it in a year or so. Instead of the all too frequent flashes of blue, red and yellow that often present themselves, we saw a single circular dot of pure white. And we saw the Pup, or at least Ernie and I did though Francine was so lucky. The apodizing mask was connected this time with a spring tension set of holders to the set screws that hold the dew shield on. This was a clear improvement over the earlier attempt to use tape and tie the mask onto the camera mount. A little harder to put on but better. The theme and variations part came in the use of a polarizing filer (both the 1.25" and the 2" variable neutral filters). They definitely reduced the light of Sirius A but they also dimmed Sirius B. I can't remember if Ernie saw anything of the Pup through the filters but I didn't.

We also tried a wide variety of magnifications from 138 to 308 diameters. Our best luck was with our very nice 19mm 1.25 eyepiece. We seem to neglect this eyepiece all too often but we shouldn't. I think the reason we overlook it, is that its slot in the eyepiece chest is in the back corner. At about 250 diameters it provided a very crisp and stable image.

When we turned to Rigel, the view was absolutely gorgeous. Both Rigel and its faint companion formed excellent images. Rigel outshines it companion by about 1500 times and the separation is about 9 arcseconds. In contrast Sirius outshines its companion by nearly 10,000 times and is about 8 arcseconds apart. Given that Rigel is 87 times farther away than Sirius, this means that Rigel's absolute magnitude is about a whopping 1400 times that of Sirius. [An absolute magnitude is the brightness of the star at a standard distance of 10 parsecs - about 32.6 light years].

Some references state that Rigel is a single star making the companion an "alignment" double. Others state that Rigel is a true double. I simply don't know who is correct. If however, Rigel is a true double then the companion is extremely bright in its own right. In fact, brighter than Sirius at a standard distance. And Sirius is the brightest of the nearest hundred stars in absolute magnitude. The two brightest stars of Alpha Centauri, then the Sun and then Epsilon Eridani are the only reasonably bright stars in the nearest hundred. In fact, most of the nearest 100 stars are not visible in anything less than an 8" telescope. Proxima Centauri (the third star in Alpha Centauri) is the closet star other than the Sun. It is too faint to be seen even in binoculars (assuming you aren't using specialized huge comet binoculars).

-Les Coleman

Leslie Coleman
Author:
Leslie Coleman
Entry Date:
Feb 29, 2008
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Leslie Coleman's Log
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