I spent a good chunk of last night in a place where I could just barely see the Milky Way, looking for the Crab Nebula, and I couldn't find it. I'm obsessed with trying to find the North American nebula too, and so far no luck. Shouldn't I be able to see them in an 8" Dob? I've got both the Skyglow and Ultrablock filters.
observing nebula
Started by mary hofer, 10/06/2002 08:21PM
Posted 10/06/2002 08:21PM
Opening Post
Posted 10/06/2002 10:43PM
#1
If you can tell us what's your sky limiting magnitude (i.e. the magnitude of the dimmest star you can see naked eye), it may help us to help you better, Mary.
Having said this, under a nominal mag 5.5 sky of my backyard, I had a hard time seeing the North American Nebula *without* filter. With UHC (akin to the Ultrablock), it was so obvious with my 4" TV-102 APO refractor. The 8" Dobs ought to see it. But here is an object where wide field scope (such as wide field small refractor) is the more appropriate instrument; it's too large to fit into the FOV of your 8"; so you may need to pan around.
The Crab is also easily visible and bright through my 4" **without** filter, though the fine tendrils were not seen :-(. So your 8" Dobs ought to be able to do it. Check your collimation, cooldown, sky transparency etc. Also, the Crab may be too low unless you stay up all night ;-). So you may want to wait until later this year.
Most importantly, please keep at it; they can't escape you for long ;-).
Ron B[ee]
Having said this, under a nominal mag 5.5 sky of my backyard, I had a hard time seeing the North American Nebula *without* filter. With UHC (akin to the Ultrablock), it was so obvious with my 4" TV-102 APO refractor. The 8" Dobs ought to see it. But here is an object where wide field scope (such as wide field small refractor) is the more appropriate instrument; it's too large to fit into the FOV of your 8"; so you may need to pan around.
The Crab is also easily visible and bright through my 4" **without** filter, though the fine tendrils were not seen :-(. So your 8" Dobs ought to be able to do it. Check your collimation, cooldown, sky transparency etc. Also, the Crab may be too low unless you stay up all night ;-). So you may want to wait until later this year.
Most importantly, please keep at it; they can't escape you for long ;-).
Ron B[ee]
Posted 10/07/2002 07:13AM
#2
Mary,
The crab nebula is small and has a relatively high surface brightness. Unless your observing conditions are very poor, you should be able to see it in your 8-inch Dob. I would recommend a power of 40 - 80x. Look for a relatively small, elongated patch of light, and don't expect to see anything resembling photographs of the nebula. The filaments easily seen in photos require a very powerful telescope.
The North America nebula is a very difficult object to observe. I have a high-class 8-inch Dob myself, and sometimes observing conditions are excellent. Even with an O-III filter, the nebula is not directly easy to see. it is very large, and you can not bring the whole nebula into the field of view - the nebula is simply too large.
The famous Veil nebula in Cygnus, also considered to be a difficult object is much easier to see in an 8-inch. But for the sake of training, I would recommend you to practice on some of the planetary nebulae first. M27 in Vulpecula is a good object, large and bright. The ring nebula in Lyra (M57) is smaller, but easy to locate, and its light output is comparable with the Crab nebula. M57 is smaller, though.
There are many gaseous nebulae within the range of an 8-inch scope, but most of them require much practice and good observing conditions. If your sky background is light or you are distrubed by ambient light, objects like the North America nebula are virtually impossible to see, and filters don't help much.
The crab nebula is small and has a relatively high surface brightness. Unless your observing conditions are very poor, you should be able to see it in your 8-inch Dob. I would recommend a power of 40 - 80x. Look for a relatively small, elongated patch of light, and don't expect to see anything resembling photographs of the nebula. The filaments easily seen in photos require a very powerful telescope.
The North America nebula is a very difficult object to observe. I have a high-class 8-inch Dob myself, and sometimes observing conditions are excellent. Even with an O-III filter, the nebula is not directly easy to see. it is very large, and you can not bring the whole nebula into the field of view - the nebula is simply too large.
The famous Veil nebula in Cygnus, also considered to be a difficult object is much easier to see in an 8-inch. But for the sake of training, I would recommend you to practice on some of the planetary nebulae first. M27 in Vulpecula is a good object, large and bright. The ring nebula in Lyra (M57) is smaller, but easy to locate, and its light output is comparable with the Crab nebula. M57 is smaller, though.
There are many gaseous nebulae within the range of an 8-inch scope, but most of them require much practice and good observing conditions. If your sky background is light or you are distrubed by ambient light, objects like the North America nebula are virtually impossible to see, and filters don't help much.
Posted 10/07/2002 08:27PM
#3
I manage to see the Crab in a 5" refractor from my urban backyard on a good night. "Good" for this site means Milky Way suspected near the zenith, so you should be able to find it in your 8" at your site. Under my observing conditions, it seems more obvious in a wider field of view. Try a 32mm eyepiece and look for that small patch of haze. Avoid the Ultrablock here, it will filter out most of M1's light; not sure whether the Skyglow would help.
As for the North American Nebula, you might be able to see at least "Gulf of Mexico" region with your Ultrablock filter, but you really need a site where the Milky Way is obvious. I have spotted it in binoculars on a good night, 60 miles out of Seattle. The nebula is probably bigger than your widest field of view, so you'll have to pan around to take it all in.
Dave Brodeur
As for the North American Nebula, you might be able to see at least "Gulf of Mexico" region with your Ultrablock filter, but you really need a site where the Milky Way is obvious. I have spotted it in binoculars on a good night, 60 miles out of Seattle. The nebula is probably bigger than your widest field of view, so you'll have to pan around to take it all in.
Dave Brodeur
Posted 10/12/2002 12:02PM
#4
Mary,
Given your visual limiting magnitude I'll venture to say that NGC 7000 (the North America, not North American, Nebula) will be next to impossible to see. This is a very expansive nebula and is best seen with binoculars and small rich-field telescopes using narrowband (UHC, UltraBlock, etc.) or O-III filters (see http://www.cloudynights.com/howto/filters.htm). At sites where the Milky Way is rather obvious the North America Nebula should be visible. At very dark sites it will be sharply delineated and the more difficult Pelican Nebula may be discernible as well.
M1 does not require a particularly dark sky or nebula filtration although broadband and narrowband filters will improve some of the Crab Nebula's aspects. I've logged M1 with my Celestron 20x80's from dark sites.
Dave Mitsky
Given your visual limiting magnitude I'll venture to say that NGC 7000 (the North America, not North American, Nebula) will be next to impossible to see. This is a very expansive nebula and is best seen with binoculars and small rich-field telescopes using narrowband (UHC, UltraBlock, etc.) or O-III filters (see http://www.cloudynights.com/howto/filters.htm). At sites where the Milky Way is rather obvious the North America Nebula should be visible. At very dark sites it will be sharply delineated and the more difficult Pelican Nebula may be discernible as well.
M1 does not require a particularly dark sky or nebula filtration although broadband and narrowband filters will improve some of the Crab Nebula's aspects. I've logged M1 with my Celestron 20x80's from dark sites.
Dave Mitsky
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