Re: (IAAC)Object:- Cat's eye Nebula 20" Dob-Newt
Sept 22 and 23
>At 11:14 10/09/97 -0400, you wrote:
>>Very intriguing post, NJM! I enjoyed the fact that you posted both a finding
>>technique for beginners, and some real details for those who might want to
>>the Cat's Eye another look. BTW, apropos an earlier thread, how did you find
>>the UHC filter changed the appearance of this weird planetary? I'd expect
>>intriguing differences in emission patterns from "normal" planetaries!
>>Clear skies all!
Dear Lew et al.
At last some darker skies again although 23 Sept was a bit hazy which made
the sky somewhat brighter than optimium.
I tried observing the Cat's Eye nebula using both the UHC and my newly
aquuired OIII filter as well as unfiltered. Very rough ASCII diagram.
**####** * "wings"
***####** # "body"
Both the UHC and OIII show the roughly rectangular body of the nebula with
high contrast but compared with the unfiltered views the "wings", which give
it the eye shape, are less conspicuous. This must reflect some differences
in the spectral emmision of the different parts. Interestingly the "body"
corresponds to the red part on the Hubble image and the "wings" to the green
false colour(?) areas. My observations on both nights confirmed the apparent
red edge visible most clearly in the "wings". I observed it through a vertex
face of a 45 degree prism to get some spectral dispersion. The blue green
body was unchanged but a red component was visible as an arc following about
2/3 of the edge of the unfiltered image appearing to correspond the red edge
visible in the lower magnification images. The sky was brighter than on the 22
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