by David Kingsley
Yes, it's that time of the lunation... the moon is waxing, it's visible in the evening sky, and I churn a series of overwrought ORs. This time it's even worse: I'm feeling fat and sassy after baggin several of Charles Wood's 'L100' targets, including number 90.
I really enjoy your moon reports Marek. Keep them chumming. Saturday night at Henry Coe the moon in very steady seeing had breathtaking detail, by far the best target of the night. I didn't have my Rukl's atlas with me so simply wandered the terminator. Your detailed report from Foothills park put names to many of the features that had looked so striking through the eyepiece.
Sunday night I set up my 7 inch Starmaster in the driveway, and again found very stable seeing around 10 pm. When I saw Serenity near the terminator I also decided to go inside, get out the Rukl's atlas, and finally hunt down craters Armstrong, Collins, and Aldrin near the Apollo 11 landing site (must be something in the South Bay air). Armstrong was visible constantly, and Collins and Aldrin could also be held for long periods of time at about 240x, once I knew where to look. Crater hopping was at least as much fun as star hopping, with tons of interesting detail to see along the way!
The seeing was steady enough that I tried some double stars as well. Porrima (gamma Virgo) has been moving rapidly the last few years, as it approaches the near point of its first orbital pass since John Herschel and others 19th century observers were watching it intensively in the 1830s. When I first looked at it back in 1998, 1999, and 2000 the two matched stars of the binary were separated by about two arcseconds and still easily splittable in a 70 mm Ranger. Last night Porrima looked slightly elongated at 240x, so I pulled out a 5x Powermate and increased the magnification to around 600X. At that power the binary was very clearly notched much of the time, and at the best moments looked like two separate boulders of a cosmic snowman stocked one on top of another. The snowman was clearly leaning left of vertical, and I estimated the position angle by comparison to the direction of westward drift through the eyepiece. Last night's estimate of 195 degrees is already 90 degrees different than the position when I was first checking in 1998. See http://www.homepages.hetnet.nl/~nbhogeveen/gamma_vir.htm for some diagrams of the orbit, and amateur images illustrating the motion over the last several years. The separation distance of Porrima is now less than 0.6 arcseconds, the Dawes limit for my 7 inch scope. It is going to get even tougher for the next two years, and will rapidly sweep through more than 90 degrees of orbital motion before popping out again into easier visibility. I love this system for its reach back into history, and the chance to watch star orbits in your own backyard.
The warm weather and high pressure system we have been under for the last couple of days may bring more steady seeing tonight, another excellent chance to check out the moon, planets, and double stars.
Posted on sf-bay-tac Apr 26, 2004 11:43:29 PT
Converted by report.pm 1.1 Jul 10, 2004 19:35:51 PT