(IAAC) Obj: Abell 21 - Inst: 4" f/6.9 achro

anonymous at sedna.atmob.org anonymous at sedna.atmob.org
Fri Aug 3 15:09:01 EDT 2007


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Observation Poster: John Tatarchuk <tatarjj at auburn.edu>

Observer: John Tatarchuk
Your skills: Advanced (many years)
Date/time of observation: 12/17/06
Location of site: 10 miles west of Fort Davis, TX (Lat , Elev 6000')
Site classification: Rural
Sky darkness: 10 <1-10 Scale (10 best)>
Seeing:  <1-10 Seeing Scale (10 best)>
Moon presence: None - moon not in sky
Instrument: 4" f/6.9 achro
Magnification: 37X
Filter(s): OIII
Object(s): Abell 21
Category: Planetary nebula.
Class: 
Constellation: Gemini
Data: mag 10.2v  size 744"x509"
Position: RA 7h:29.1m  DEC +13:14.9'
Description:
(First observation in 4” refractor)- Abell 21 (744”x509”, mag 10.2v) in Gemini 
is probably the easiest Abell in the whole catalog, and displays a lot of cool 
structure in the 18” dob. I had first seen it many years ago but I had never 
seen it- and never tried to see it- in my 4” refractor. I suspected it would 
be fairly easy, and I was right. On 12/17 I decided to give A21 a go in my 4” 
Stellar Vue achromat. At 37X with OIII filtration, I found Abell 21 to be a 
very easy object in the tiny scope, appearing as a crescent-shaped glow. None 
of the arcs and filaments that are visible in larger apertures (and give it 
the name “Medusa Nebula”) were visible, however.

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