Planetary nebula can be very difficult, or very easy objects. The easy ones I'll not talk about, such as the ring nebula or the blue snowball. Those should be easily found in smaller scopes.
This years Stellafane convention held an observing olympics that was dedicated to planetary nebula, many of which were listed in sizes of 20-30 arc-seconds and magnitudes from 9 to almost 15!! Initially, before trying my first object, there seemed to be enough nebula of the list of 25, to capture 15 of them in my 7" refractor.
My experience in the end was good, but after an hour in the beginning I didn't think I'd be successful. Here is what I found.
First what I was using. I had a 7" refractor with a focal length of 1260mm. I also used digital setting circles which greatly helped me zero in on the objects. Probably not the best scope for this kind of tiny object but the digital setting circles helped this. Initially I went with a 10mm ocular which gave a 126X magnification (not much) and a field just over .56 degrees. This meant that most of these objects in the 20-30" range would be 1/60 my FOV!!!
The other fact, not initially obvious to me is that while we had the spec'd size of each object, the objects can appear vastly different as that brightness of these objects doesn't always go out to the full size, some of them are brighter in a central portion which can be much smaller than the size. My early attempts at some objects were failures because the nebula, while visible in my FOV, was not identified as a nebula and looked like a star. If I would have gotten full star maps out, and compared fields, I would have identified them earlier. So I skipped around the list, and as I did so, I did find some objects that looked bigger than objects of the same size, that appeared much smaller. The ones that helped me identify this discrepancy were those that were flattened, not circular, like the Saturn nebula which is a full 70", but much smaller in the FOV than I expected, but was easily identified due to it being oblate. This lead me to go back and look for some of the earlier objects, like the very first on the list, IC4593, with a different expectation, and there it was close to the center of the field! I put in a 3.5mm ocular and there it was, larger than life (not really big, just clearly not a star). I also changed my eyepiece to use an 8mm instead of the 10 for searching.. this helped give me some size to the smaller objects in the 20-30" range and also helped bring out a bit of color in some of them. That said, there were many I thought I should find, but did not. I am going to continue looking for the ones within the light grasp of my telescope from home, to see if I can locate them. I'm also going to try from a driven mount as using high magnification helps the process, but with an un-driven mount, it's difficult to keep your object in the field at 300X as you're changing eyepieces in the dark!!
So you really do need a couple of processes to surely identify these small fascinating objects: One is having the right expectation for size in the eyepiece. Two is using a star chart to understand where the object sits within a field (or like me, using digital setting circles).
Terri
One long-term project I have going (very slowly) is observing the Minkowski planetary nebulae. (The Minkowski catalog of PNs has around 200 PNs.) When I started I found a couple of them and thought doing this list would be fun and easy. But the PN's on the list vary a huge amount in how difficult they are to see. Many of these PNs appear like slightly fuzzy stars. But some appear stellar, stellar, stellar. For these, an OIII is essential. That is, I'll hold an OIII in my hand and 'blink' it by looking through the EP, then put the OIII between my eye and EP and remove it, all in fairly quick succession. The OIII makes all the stars much darker but the PNs don't darken, so they stand out. Pulling a few up from the list I've seen, I see a one is 15" is size and one is 3". They also vary hugely in brightness. For quite a few that I've tried to find, I've been unsuccessful (so far) using the 18" scope.
Mark
@Terri What mount did you use for this, Terri? Can you share the list of the planetary nebulae (so as to narrow down the list I'm looking at in my Pocket Sky Atlas)?
Thanks for the great information!
Greg
One long-term project I have going (very slowly) is observing the Minkowski planetary nebulae. (The Minkowski catalog of PNs has around 200 PNs.) When I started I found a couple of them and thought doing this list would be fun and easy. But the PN's on the list vary a huge amount in how difficult they are to see. Many of these PNs appear like slightly fuzzy stars. But some appear stellar, stellar, stellar. For these, an OIII is essential. That is, I'll hold an OIII in my hand and 'blink' it by looking through the EP, then put the OIII between my eye and EP and remove it, all in fairly quick succession. The OIII makes all the stars much darker but the PNs don't darken, so they stand out. Pulling a few up from the list I've seen, I see a one is 15" is size and one is 3". They also vary hugely in brightness. For quite a few that I've tried to find, I've been unsuccessful (so far) using the 18" scope.
Mark
Hi Mark, we had one Minkowski on the list that I did not find. I did take out a nebula filter at one point, but maybe I should have taken out an OIII and just left it on there. As I continue to hunt them down in my yard, I'll try this. When I tried the nebula filter, the view became very dark, but given how little I get to do visual I didn't know the benefit. Maybe this would have been the way to go. The one I didn't find is Minknowski 1-64. We had Hubble4, at 6" and mag 13.1!!!! We had a few other 13.X and a 14.5! Luckily, I only needed 15 of 25 as the 13.Xs I did not get except the little gem at 13.2, which I think brighter than 13.2.
Terri
@terri Hi Terri, The observing Olympics sounds like it was fun -- I'm jealous!
Of the Minkowskis I've found, I'm guessing 2/3 of them I wouldn't have been able to find without an OIII. Even if you can find it without an OIII, the OIII still helps.
My notes for M 1-64 include: "Responds well with OIII. Looks sharper with OIII."
And for the fainter ones, I assume aperture is the main limiting factor.
@terri Hi Terri, The observing Olympics sounds like it was fun -- I'm jealous!
Of the Minkowskis I've found, I'm guessing 2/3 of them I wouldn't have been able to find without an OIII. Even if you can find it without an OIII, the OIII still helps.
My notes for M 1-64 include: "Responds well with OIII. Looks sharper with OIII."
And for the fainter ones, I assume aperture is the main limiting factor.
Hi Mark, I was a bit flustered when I performed poorly at the beginning of the night, and almost threw in the towel. It took me until the clouds rolled in around midnight or so to just get 15, and one of those with the help of a neighbor who had a large scope (a lot like our own 18" obsession). I was looking and couldn't find an object and then I overheard him telling his wife/girlfriend, "I've got (the same object) in the viewfinder, do you want to look?" so I went over and asked.. it was big and beautiful in his scope.
I ended up getting my pin, but I really wanted to get all 15 in my own scope and I failed in the end. The one I kept trying, and did not find was the blinking planetary nebula, ngc6826 and I know I've looked at this one before. It's fairly bright.. so that's my first target on a clear night. In fact I talked to the guy who created the list and told him how much more difficult it is than the last few years, and he told me he'd been easy on us because he didn't think there were any real observers, just a bunch of telescope makers. And he said this year proved him wrong with how many got the pin the first night. I think there were 30 of us. I never did get to the bino list. Saturday after 10:30 turned out nice as well and even better than Friday, but I didn't sleep well the night before so I was exhausted and did some viewing with my neighbor in his 20" drive ball scope (very cool home made scope).
One of the other things I didn't mention, which culled my list quite a bit, is the fact that I was using a long refractor on a tripod. When trying to view items near the zenith (in vega or cygnus), My scope just wouldn't go there because I was hitting the tripod legs. It was a bit frustrating as this took away a number of objects from my list.
It is fun, and you would be a master at it. I suspect you could be teaching classes in finding things. You should come to Stellafane next year!
Best,
Terri
@Terri What mount did you use for this, Terri? Can you share the list of the planetary nebulae (so as to narrow down the list I'm looking at in my Pocket Sky Atlas)?
Thanks for the great information!
Greg
Hey Greg, sorry I missed this at first. I used a 6" discmount alt-az manual mount. Not really the best for anything that requires high mag. It's a great manual mount with encoders and a nexus DSC, but when you have narrow FOV with high power eyepieces and changing eyepieces while trying to keep something in view, it's a challenge. I'm sure for someone better, it's easier, but it was difficult for me. I did it a few times and moved to a 3.5mm eyepiece, but wow, things are moving fast. I have a turret, but using the turret with a tripod and long refractor makes the issue near the zenith even worse due to how broad the turret is with eyepieces. I actually tried it while in michigan and it's a very cool thing to be able to spin the turret to your next or highest power and back to lowest power in less than a second but you loose too much of the sky. I think the ultimate for me would be the 180 with turret on a driven pier, and either the mach 2 or 1100. Either would be fine for visual. But I'd want a big pier, like my ATS pier as it's 54" long so I'd have the best chance to clear the pier with the turret at the zenith and not have my cheek on the ground. next year this is what I'm going to do!!
Terri
@terri Thanks for the info, Terri, I was curious. Well, sounds like you had fun and have a plan for next year!
Greg
Well, I had the opportunity to point my8” SCT at some of the targets I didn’t find at Stellafane after most of the guests had left Joe’s outreach event. The SCT does have fairly good goto, so the targets were easily found and stood out well from the background. The blinking planetary showed significant details including the inner/outer shells and inner details. I was surprised at how well the nebula stood out from the background, which leads me to believe the SCT is a good scope for hunting these planetary nebula.
T
