Messier 21 (M 21)

Introduction | Map | My Own Photos | My Own Observations | References

On this page I collect my observations of the open star cluster M 21 (NGC 6531) in the constellation Sagittarius.

Introduction

The open star cluster M 21 is located in the constellation Sagittarius and is, according to Stoyan, often given little attention to. To him, it is attractive, because it can be observed with the telescope with M 20 (Trifid Nebula) in the same field of view (40').

In a Vespera (Pro) mosaic M 21 can be seen together with M 8, M 20, and some other DSO.

M 21 (NGC 6531)
Size: 7' (Stoyan)
Distance: 4,000 light years (Stoyan)
Rating: * (Stoyan)

Map

M 21 in the constellation Sagittarius and in the context of other nearby DSO; M 20 is directly below it, and both can be observed together in a telescope. (Image Courtesy of SkySafari Astronomy, www.simulationcurriculum.com)

My Own Photos

eVscope


M 21 - May 29, 2020, disturbed	M 21 - Aug 23, 2020	M 21 - Aug 23, 2020, photo left processed

	M 21 - Jul 18, 2021	M 21 - Jul 18, 2021, photo left processed

Vespera Pro

M 20 and M 8 / M 20, M 8, and M 21


M 8 and M 20 - Jun 25, 2024, 2000p (217 frames, 2170s), mosaic		M 8 and M 20 - Jun 25, 2024, 2000p (217 frames, 2170s), mosaic, processed (PSE)

M 8 and M 20 - Jun 25, 2024, 2000p (217 frames, 2170s), mosaic, processed (PSE) and denoised (DN)		Evaluation with nova.astrometry.net

M 8, M 20, and M 21** - Aug 5, 2024, 2000p (103 frames, 1030s), mosaic		M 8, M 20, and M 21 - Aug 5, 2024, 2000p (103 frames, 1030s), mosaic, processed (PSE)

M 8, M 20, and M 21 - Aug 5, 2024, 2000p (103 Frames, 1030s), mosaic, processed (PSE) and denoised (DN)		Evaluation with nova.astrometry.net **

M 8, M 20, and M 21*** - Aug 6, 2024, 2000p (162 frames, 1620s), mosaic		M 8, M 20, and M 21 - Aug 6, 2024, 2000p (162 frames, 1620s), mosaic, processed (PSE)

M 8, M 20, and M 21 - Aug 6, 2024, 2000p (162 frames, 1620s), mosaic, processed (PSE) and denoised (DN)		Evaluation with nova.astrometry.net ***

*/***) Further DSO: IC 1271, IC 1274, IC 1275, IC 4678, IC 4681, IC 4684, IC 4685, NGC 6526, NGC 6546, NGC 6559, M 21 (NG 6531)
**) Further DSO: IC 1271, IC 1274, IC 1275, IC 4678, IC 4681, IC 4684, IC 4685, NGC 6506?, NGC 6526, NGC 6546, NGC 6559, M 21 (NG 6531)

M 21 from Second Mosaic

M 21 - Aug 5, 2024, 1800p (217 frames, 2170s), mosaic, 1:1 section from mosaic

My Own Observations

Observations September/October 2019

Sep 28, 2019 (Sumène, France: StarTravel 120/600 on AZ Pronto Mount): M 21 (eyepieces ?): Only stars, not really identified (only position: small triangle in rhombus).
Oct 3, 2019 (Sumène, France: StarTravel 120/600 on AZ Pronto Mount): M 21 (24 mm) fine stars seen.

Observations May to August 2020

May 29, 2020 (Erkerode: eVscope): M 21 photographed, strongly disturbed
August 23, 2020 (Mühlhausen/Kraichgau: eVscope): M 21 photographed

Observations July 2021

July 18, 2021 (Mühlhausen/Kraichgau: eVscope): M 21 photographed (n.o., r.f.), new image size and processing, poor collimation despite new collimation

Observations June to August 2024

June 25, 2020 (Mühlhausen/Kraichgau: Vespera Pro): M 20 photographed together with M 8 and some more DSO as a mosaic, M 21 at the edge...
August 5, 2024 (Mühlhausen/Kraichgau: Vespera Pro): M 21 photographed together with M 8, M 20, and some more DSO as a mosaic, disturbed
August 6, 2024 (Mühlhausen/Kraichgau: Vespera Pro): M 21 photographed together with M 8, M 20, and some more DSO as a mosaic

References

Messier Catalogue - Messier 21: messier.seds.org/m/m021.html
Messier 21 (Wikipedia): en.wikipedia.org/wiki/Messier_21