wvreeven
August 14th, 2016, 07:47 PM
NGC 6914, vdB 131 and vdB 132
HII region with Reflection Nebulae
Constellation: Cygnus
RA: 20 25 00.0
DEC: +42 18 00
This nebula complex was discovered by Jean Marie Edouard Stephan in 1881. Howard already told us the story of Jean Stephan (http://www.deepskyforum.com/showthread.php?794-Object-of-the-Week-November-1-2015-Stephan-s-Quintet-HCG-92-Arp-319). Sidney van den Bergh added two of the three reflection parts to his 1966 Catalogue Of Reflection Nebulae.
According to Harold Corwin on ngcicproject.org, the designation NGC 6914 only applies to one of three reflection nebulae that lie close together. The other two therefore must be vdB 131 and vdB 132.
Several sources, that can be found via Google, claim, however, that all three reflection nebulae together are called NGC 6914 and vdB 131 applies to the western most one and vdB 132 to the remaining two nebulae.
SkyTools has a different naming scheme yet again, where the western most part is vdB 131, the center one vdB 132 and the northern most one Bernes 25 and NGC 6914 is vdB 131 and 132 together. A forth part, called Bernes 22, lies slightly south.
The designations used by SkyTools seem to come from Simbad, though there NGC 6914 is the bright part of the northern most reflection nebula (in accordance with Corwin) and Bernes 25 a detached, small part to the southwest of NGC 6914.
In short: the naming of these objects is quite messy and I am not sure anymore which part is which. I did find this annotated image of the region online, which seems to favor the Simbad naming.
2223
According to the information published with APOD of March 4, 2011 (http://apod.nasa.gov/apod/ap110304.html), the nebula complex lies about 6000 light years from Earth. The dark clouds seen towards the nebulae lie in the foreground. The atoms in the HII region get excited by the ultra violet emission from massive, hot, young stars in the Cygnus OB2 association, while visible light coming from the same stars gets reflected by dust in and near the HII region.
So, why should this nebula complex be of interest to you? Whenever I am observing reflection nebulae, I always wonder a bit whether the glare I see around stars really is the reflection nebula, or if my optics merely need cleaning.
Not with these nebulae! My 20" already shows hints of the nebulae at 83x (the lowest magnification I apply using a 31 mm Nagler) without a filter and at 151x (17 mm Ethos) and even 256x (10 mm Ethos) the nebulae are very clearly visible. At 256x I can even see hints of the dark clouds hovering in front of the northern most reflection nebula, especially to the west of the double star embedded in the nebula. The nebula has a sharp edge there and exceedingly faint bits are visible further west. I suppose that is Bernes 25, by the way. Both vdB 131 and vdB 132 stand (relatively) high magnifications as well, though they remain but glares around a triplet and a double star respectively. I didn't try for Bernes 22, nor for the Lynds Darka and Bright Nebulae (LDN and LBN) because I only realised they exist while I was writing this text. I did try to observe the reflection nebulae with my UHC filter and nothing remained visible of them, so that proves their true reflection nature. I didn't notice any nebulosity in other parts of the sky around there, so maybe the LBN objects are too faint or extended to be observed well with a 20" telescope. Maybe a smaller telescope with a wider FOV does show them under very dark skies.
In other words, lots of challenges in this area of the sky! As always,
"Give it a go and let us now!"
HII region with Reflection Nebulae
Constellation: Cygnus
RA: 20 25 00.0
DEC: +42 18 00
This nebula complex was discovered by Jean Marie Edouard Stephan in 1881. Howard already told us the story of Jean Stephan (http://www.deepskyforum.com/showthread.php?794-Object-of-the-Week-November-1-2015-Stephan-s-Quintet-HCG-92-Arp-319). Sidney van den Bergh added two of the three reflection parts to his 1966 Catalogue Of Reflection Nebulae.
According to Harold Corwin on ngcicproject.org, the designation NGC 6914 only applies to one of three reflection nebulae that lie close together. The other two therefore must be vdB 131 and vdB 132.
Several sources, that can be found via Google, claim, however, that all three reflection nebulae together are called NGC 6914 and vdB 131 applies to the western most one and vdB 132 to the remaining two nebulae.
SkyTools has a different naming scheme yet again, where the western most part is vdB 131, the center one vdB 132 and the northern most one Bernes 25 and NGC 6914 is vdB 131 and 132 together. A forth part, called Bernes 22, lies slightly south.
The designations used by SkyTools seem to come from Simbad, though there NGC 6914 is the bright part of the northern most reflection nebula (in accordance with Corwin) and Bernes 25 a detached, small part to the southwest of NGC 6914.
In short: the naming of these objects is quite messy and I am not sure anymore which part is which. I did find this annotated image of the region online, which seems to favor the Simbad naming.
2223
According to the information published with APOD of March 4, 2011 (http://apod.nasa.gov/apod/ap110304.html), the nebula complex lies about 6000 light years from Earth. The dark clouds seen towards the nebulae lie in the foreground. The atoms in the HII region get excited by the ultra violet emission from massive, hot, young stars in the Cygnus OB2 association, while visible light coming from the same stars gets reflected by dust in and near the HII region.
So, why should this nebula complex be of interest to you? Whenever I am observing reflection nebulae, I always wonder a bit whether the glare I see around stars really is the reflection nebula, or if my optics merely need cleaning.
Not with these nebulae! My 20" already shows hints of the nebulae at 83x (the lowest magnification I apply using a 31 mm Nagler) without a filter and at 151x (17 mm Ethos) and even 256x (10 mm Ethos) the nebulae are very clearly visible. At 256x I can even see hints of the dark clouds hovering in front of the northern most reflection nebula, especially to the west of the double star embedded in the nebula. The nebula has a sharp edge there and exceedingly faint bits are visible further west. I suppose that is Bernes 25, by the way. Both vdB 131 and vdB 132 stand (relatively) high magnifications as well, though they remain but glares around a triplet and a double star respectively. I didn't try for Bernes 22, nor for the Lynds Darka and Bright Nebulae (LDN and LBN) because I only realised they exist while I was writing this text. I did try to observe the reflection nebulae with my UHC filter and nothing remained visible of them, so that proves their true reflection nature. I didn't notice any nebulosity in other parts of the sky around there, so maybe the LBN objects are too faint or extended to be observed well with a 20" telescope. Maybe a smaller telescope with a wider FOV does show them under very dark skies.
In other words, lots of challenges in this area of the sky! As always,
"Give it a go and let us now!"