>Rich N wrote:
>>Late, after midnight I tried splitting Porrima. It was easy to see
>>that it was a
>>double star but no black line between the Airy discs. It was just
>>at the point
>>of starting to show a figure eight. I was using well over 400x. One of the
>>observers though maybe it would have shown the split if the seeing had been
>>dead steady. I was happy the way it looked given it is very close
>>for my 6.1"
>>scope. Two years ago it was easy to see a black line between the two stars.
>
>
>I checked the Porrima orbit today and found that the A and B
>components are currently only separated by 0.51 arcseconds. That is
>well under the Dawes limit for a 6.1 inch scope. Getting Porrima to
>a figure 8 at this separation already sounds like you had a very
>good night.
>
Most of the time Porrima looked very elongated. Only at
the best moments did it look like it was just starting to show a
figure 8 (slightly pinched).
One of the people at the star party thought it was about 0.70.
At 0.58 I'm really happy we could tell it was a double.
Rich
>
>Rich also wrote:
>>Two years ago a couple of us made two or three trips to the site a
>>little below
>>Montebello
>>to test a new telescope, using Porrima as a target. Porrima was a
>>little more open
>>giving me a nice clean split in my 155mm.
>
>
>For others who have looked at this star before and may be interested
>in how it is changing, here is the Binary Star Orbit Ephemeris for
>the A-B components of gamma Virgo (calculated from SkyTools binary
>star orbit tool)
>
>Year/Month Angle Separation distance
>1998 Apr 25 267.0 1.73
>1999 Apr 25 262.8 1.57
>2000 Apr 24 257.6 1.39
>2001 Apr 25 250.7 1.20
>2002 Apr 25 241.1 1.00
>2003 Apr 25 226.1 0.77
>2004 Apr 24 196.8 0.51
>2005 Apr 25 126.7 0.37
>2006 Apr 25 67.3 0.58
>2007 Apr 25 44.3 0.86
>2008 Apr 24 32.4 1.12
>2009 Apr 25 24.8 1.35
>
>
>Note that Porrima was easily splittable through 2002, but has been
>getting tougher in 2003 and 2004. Next year is the year of closest
>approach, and will be particularly difficult. As the components
>reach their minimum distance, the position angle of the system will
>also be changing orientation at over 5 degrees per month. (Systems
>in elliptical orbits sweep out an equal area of the orbit each year.
>When the components are at minimum separation, they charge past each
>very quickly, making up in orbital path length what they lack in
>physical separation).
>
> At Porrima's current rate of orbital change, it should be possible
>to see a change in position angle of the AB components within the
>2004 observing season. I estimated a position angle of 195 degrees
>last night, and was happy to see how close that was to the actual
>orbit when I checked today in SkyTools. (Position Angle Estimators
>Unite! Jamie Dillon recently mentioned on TAC the small observing
>rush that comes from making and galaxy position angle estimates in
>the eyepiece that can later be confirmed in catalogs or images of the
>field. It also increases my confidence that I didn't just
>hallucinate the Porrima observation last night with high
>magnification in the 7 inch scope). By this summer, the two
>boulders of the gamma Virgo snowman may be standing nearly straight
>up (position angle 180 degrees) as Porrima drifts west through the
>eyepiece.
>
>David Kingsley
>
>
>
Received on Mon Apr 26 18:33:23 2004