Hi all...had two cracker nights of seeing last week - probably some of the best ever...so I thought why not have a crack at the Blue Planetary Nebula...had my star chart and mobile observatory app and was real excited...nah, couldn't see it! I sware I was in the right spot, just to the right of the southern cross...took my time too, but it still eludes me...
Your equipment is not shown, so what were you using to try and see it?
It is small[12" diam] and bright blue/green. When you are certain that you are in the right area you will have to increase the magnification in order to pick it out from field.
raymo
Its not in the least fuzzy, its sharp and bright, but very small. A 9mm EP
will make it larger, and hence easier to spot, but will obviously give you
a smaller field of view with a correspondingly higher chance of it being
outside of that field of view. Perhaps a 12mm to 15mm would give you a
better chance of locating it, and then up the power when you find it.
raymo
One of the best tools for locating planetary nebula is an OIII filter.
One like this will work very well, what you do is hold it and with an eyepiece with decent eye relief move it in front of your eye and back a few times. This is known as blinking. Normal stars will dim very noticeably, but the PN will not.
If only using for locating an inexpensive OIII filter will do. Bintel used to do a rebadged GSO one, shop around and you may still find one somewhere.
Thanks Malcolm...is that anything like the greenie filter I have that makes Eta Carinae and the Orion nebulas stand out? (That is a super helpful filter!)
Maybe. Does the filter have anything written on it? Most likely would be UHC or OIII but it may be something else.
If it is not an OIII filter (BTW OIII means "O3", meaning doubly ionised oxygen. It isolated a very narrow band of light emitted by ionised oxygen which is commonly found in the light from Planetary nebula) it will not be able to be used for this blinking procedure.
One thing needs to added to using a filter to suss out planetaries. Most planetary nebulae are tiny. Even the Blue Planetary, though it is actually quite bright, its angular size is actually very small. This is part of the reason that it is bright is that it is so small. If it were larger in diameter, it would appear dimmer as its light would be spread out over a larger area.
Anyway, PN's are not always immediately obvious, be it for their size, brightness, location, etc. And while an OIII filter is invaluable in identifying them, unless you know what to look for, or the PN is very obvious, in most instances an OIII filter won't help. The Blue Planetary is an example where it really requires a lot of magnification to bring out its disc size. So unless you were anticipating this, you'll run right over, even with your OIII filter.
One brilliantly easy tool you can make that is fantastic to chase out PN's is a blinking paddle. This paddle holds a 1.25" OIII filter that you then flick between your eye and the eyepiece. If there is a PN in the field of view (FOV), the filter will make the PN literally "POP" out from the background. Once you've identified where the PN is, you can either put the filter in an EP or filter slide, or whatever, and further your examination of it. The Blue Planetary is one PN that really benefits from 'blinking' it out first if you are not to confident in identifying it.
In other instances, blinking out a PN is the only way to identify it from its surroundings. The giant open cluster M7 holds no less than 6 planetary nebulae within its boundaries (not all associated with the cluster, if any). But because M7 lies in within a rich area of the Milky Way, and the PN's are so tiny, blinking them out initially is the only way to isolate them. And it staggers me just how much these PN's leap out by blinking, and impossible to identify without doing so. Even large PN's benefit from blinking as they can have a low surface brightness, and blinking will just help identify their location.
For what it's worth, also within the celestial boundary of M7 are four other open clusters and at least one globular cluster, none of which are associated with M7, and all are just a line of sight coincidence.
Pluto was similarly first discovered by blinking, though for Pluto the blinking was done between two photographs, and the 'moving star' that was how Pluto was noticed.
Last edited by mental4astro; 26-04-2016 at 12:37 PM.
Reason: typo
Awesome info again guys! My filter is a UTC so might have to grab me an O3...little wonder I couldn't find the Blue...
I'm not sure what a UTC filter is? but if it's similar to a UHC filter than there is no need for an O3. In fact if you were to have only one filter, than a UHC filter would be it. A UHC filter does everything that an O3 does but allows for a few extra wave lengths of light through, which makes it useful for a broader range of nebulas. Astronomiks makes a nice UHC filter that I like.
Once you do find the Blue planetary, don't be afraid to pump up the magnification as far as you can go. It handles magnification very well and starts to show some structure at high magnification. Also at high magnifications you are probably better off removing the filter. High magnification alone boosts contrast and a filter will probably make things too dark.
I think for NGC3918 there is no need for any filters to see it, you simply can't miss it - it looks like Uranus with it's green colour.
See here, from light poluted Melbourne and no filters: http://www.astrobin.com/174748/
I think for NGC3918 there is no need for any filters to see it, you simply can't miss it - it looks like Uranus with it's green colour.
See here, from light poluted Melbourne and no filters: http://www.astrobin.com/174748/
At low magnification in a small telescope you can easily mistake it for a star. But at high magnification you can also miss it if you're not looking in the exact location.
Joe, I would agree that a UHC would be better to have than an OIII if only
having one filter, but a UHC does not do everything that an OIII does. There
are numerous nebulae that respond better to an OIII than a UHC, as a
glance at any of the published comparative lists will verify.
raymo
The Blue Planetary is one of my favourite things. As a newbie, finding it by star hopping was initially quite difficult, but with patience and a reasonable star chart it does appear.
I got onto it originally with a 6" SCT and have never used filters, so you should be able to get it, using good logic (your eyepiece image may be upside down or back to front or when compared to your star chart!), and above all, patience!
Yep, it is worth it!
Last edited by Greenswale; 26-04-2016 at 05:14 PM.
Reason: Fix bad grammar!
Joe, I would agree that a UHC would be better to have than an OIII if only
having one filter, but a UHC does not do everything that an OIII does. There
are numerous nebulae that respond better to an OIII than a UHC, as a
glance at any of the published comparative lists will verify.
raymo
I probably worded that a bit badly.. What I mean is that a UHC passes the same lines as an O3 plus a few others. However like you said some objects, often planetary nebula, respond better to the more restrictive O3, but a good UHC will still provide a good boost to the same objects. Overall a UHC filter is more versatile, but if you can afford it get both.
Will keep looking...!
