scottstirling on 08-Sep-2026 04:29:03 GMT about M 57
The position angle listed as 90 degrees is the default in SIMBAD when there's no data (which is confusing if the PA actually is 90 deg), and is not the best choice for M 57. HASH 4.6 (http://202.189.117.101:8999/gpne/objectInfoPage.php?id=509) lists position angles sourced from
Spatial orientation of planetary nebulae (Weidmann+, 2008)
which is in Vizier as
J/PASP/120/380
and it lists position angles of 57 deg (EPA) and 123 deg (GPA). I have tested annotation with PixInsight using the 57 degree equatorial position angle and it overlays accurately. The HASH angular dimensions for M 57 are slightly larger too, dimmajor: 1.48333 x dimminor: 1.1 arc minutes.
Currently, amateur astrophotographers are imaging M 57 in deep Halpha and exposing extended Halpha nebulosity around M 57 that is much broader than traditional measurements (see, e.g., https://astrob.in/pomids/0/, pretty typical of recent images of M 57 with lots of integration time in Halpha), but I do not have a published academic measurement source for that yet, and it may be that separate measurements are warranted for angular dimensions of the outer Halpha shell.
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View annotation on M 57 object