(IAAC) Abell 21 (PK 205+14.1; PN G205.1+14.2) - 17.5" F/4.5

Observer: Yann POTHIER (France)
Your skill: advanced (many years)
Date and UT of observation: 27 December 1994, about 00h00 UT
Location & latitude: La Clapiere Obs. (France, latN44 40 00, longE06 27 36)
Site classification: rural, alt.1650m (5500ft)
Limiting magnitude (visual in UMi): 6.0
Transparency (1 to 5 - best to worst): 1
Seeing (1 to 5 - best to worst): 2
Moon up (phase?): no
Instrument: Coulter 17.5" (445mm) F/4.5
Magnification: 87-145x
Filters used: OIII, UHC
Object: Abell 21 (PK 205+14.1; PN G205.1+14.2; Sh2-274; ARO 388)
Category: planetary nebula
Constellation: GEM
Object data: Vmag=10.3; dim.744"x670" (765"x510" in IDB); central star of
Vmag=15.99; discovered by Abell in 1955.
RA/DE: 07h29.0m, +1315' (2000); Uranometria 184
Description: at 145x, found 32' to the SE of the cluster NGC 2395; very
large PN, very faint without filter and only faint with filter; suspected
at 45x and 74x without filter, seen at 87-125-145x without filter; well
seen at 45x+UHC, 125+OIII and 145x+OIII; global crescent shape opened to
the NW, with 2 brighter zones seen with OIII; estimated diameter of the
nebula (on drawing) of about 10' (ie 600"), and the C is 4.4' (ie 265") at
its thickest parts; a brighter zone is centered on a mag11.5 star in the
northern part of the crescent: it is a parallelogram of about 6.2'x2.7'
along a NW-SE axis; another brighter area appears on the southern part of
the crescent: about 3.1'x1.4' on a E-X axis; some stars of mag14 are
scattered in the fainter center of the nebula; it is no more visible at
I can provide a scanned drawing of Abell 21 to anyone who can read the
binhex encoding of Eudora (for Mac); just mail me to try
(ypothier@abi.snv.jussieu.fr), it works sometimes with other
Yann Pothier
11 impasse Canart, 75012 PARIS, FRANCE
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