APOD and General Astronomy Discussion Forum
https://asterisk.apod.com/
FLPhotoCatcher wrote:
I notice that no one here has mentioned that the halo is hexagon shaped. How could that have happened?
There is a suggestion of hexagonal symmetry in the inner Cat's Eye as well. They are probably related to each other.Collimated outflows?neufer wrote:FLPhotoCatcher wrote:
I notice that no one here has mentioned that the halo is hexagon shaped. How could that have happened?
starsurfer wrote:Also the first PN halo was discovered in 1937 around NGC 6826 but nearly all the currently known haloes have been discovered in the 1980's, 1990's and 2000's. Another point to mention is that there are many faint PN haloes that haven't been officially published by professionals yet. Some good overviews are this paper by Bruce Balick and another by Romano Corradi. Other noteworthy publications are this one and this one. There will hopefully be a new collection this decade, a preview can be seen here.
Also I simply cannot resist including a list of some nice PN haloes:
IC 5148 by Don Goldman
Hen 2-111 by Don Goldman
NGC 5882 by CHART32
NGC 7009 by CHART32
M27 by Fabian Neyer and Robert Pölzl
There are lots of haloes out there but the majority of amateurs are unaware of them except PN obsessives. The one around the Saturn Nebula was discovered in 1998, see here. The CHART32 image might be the first amateur one to show it.Josh Smith wrote:starsurfer wrote:Also the first PN halo was discovered in 1937 around NGC 6826 but nearly all the currently known haloes have been discovered in the 1980's, 1990's and 2000's. Another point to mention is that there are many faint PN haloes that haven't been officially published by professionals yet. Some good overviews are this paper by Bruce Balick and another by Romano Corradi. Other noteworthy publications are this one and this one. There will hopefully be a new collection this decade, a preview can be seen here.
Also I simply cannot resist including a list of some nice PN haloes:
IC 5148 by Don Goldman
Hen 2-111 by Don Goldman
NGC 5882 by CHART32
NGC 7009 by CHART32
M27 by Fabian Neyer and Robert Pölzl
Thanks for those examples! PN and the outer halos are my favorite targets. So much going on in them and a lot to learn about them as well as opportunities to help advance their understanding. Good to see a couple of examples with outer halos I wasn't aware of. I may have to spend a while on the Saturn one as I didn't realize there was a halo there. Very, very few examples of that out there.
There are a few mostly unknown haloes around northern PN but not as many as southern ones. The fairly recent IPHAS hydrogen alpha survey of the northern galactic plane was completed a few years ago, so I guess if someone went through the data, some new and unknown haloes could be discovered. I don't know of anyone working on this area.Josh Smith wrote:Would be nice to know of some more Northern targets that need to be examined more closely too!
