Question M43?

[jetstream]

Recently,while observing the Orion nebula I noticed something that I hope to get confirmed and clarification on.When using my OIII filter it appeared that M43's small nebulosity(in my scope) dissapeared.Using various eyepieces in my telescope confirmed the nebulosity was easily visible without the filter.I am wondering if M43 emits different wavelengths than M42?I realize that different wavelenths are emmited,but I was wondering if anyone else noticed this?Orion was low on the horizon,during light skies when I observed this,so my conditions were much less than optimum.Even then M42 itself with the filter showed a huge amount of nebulosity,but M43's was gone.

[Double Kick Drum]

M42 and M43 are part of the same nebula but have separate Messier numbers. M43 is noticeably feinter that its illustrious partner and looks like a separate circular patch of nebulosity. I have never noticed any different effect between the two using an OIII filter. I think M43 probably disappeared simply because it does not emit enough light to overcome the effects of the filter through your scope.

[jetstream]

Thanks for the info,if it is visible to you with OIII then my 90mm isn't getting enough light for the filter.I'll try with more aperture soon.I just found it odd as it was small but distinctly there with various eyepieces.

[Stu]

I'm sure that's it. I do use an OIII in my 106mm scope but they are generally recommended for larger apertures (over 8" I think) because they cut out so much light. From a dark site it is still worth using, but a UHC, or UHC-S might be better in some circumstances.

Stu

[acey]

M43 is classed as an emission and reflection nebula - part of its light is reflected from the embedded star NU Orionis. A filter will cut this reflection nebulosity while enhancing the emission nebulosity. The filter will also cut the light from the star itself. So this most likely explains what you saw. If the filter makes M43 invisible then all the nebulosity you were seeing must have been reflection nebulosity. 

[jetstream]

M43 is classed as an emission and reflection nebula - part of its light is reflected from the embedded star NU Orionis. A filter will cut this reflection nebulosity while enhancing the emission nebulosity. The filter will also cut the light from the star itself. So this most likely explains what you saw. If the filter makes M43 invisible then all the nebulosity you were seeing must have been reflection nebulosity. 

Thanks Acey,this explains my observation completley.As the object is both types of nebula,my filter killed the reflection nebulosity and I may not have had adequate aperture to allow the OIII filter to work under my sky at the time.I remembered an article on filters http://www.prairieastronomyclub.org/resources/by-dave-knisely/filter-performance-comparisons-for-some-common-nebulae/ and the OIII worked,but was not optimum on this object.My 8mm Delos really performed on M42/M43 that night with no filter,showing a very wide set of "wings" and M43 as a great "glowing" star.The filter with the 17mm Ethos gave a much better, fuller presentation of M42,but no M43.

I can't wait until Orion is higher in the sky and I get myself out to a dark site to observe it.

[LukeSkywatcher]

Ive only ever used a UHC filter to observe the Orion nebula. I probably wouldnt even notice when using my OIII that it blocks some light from M43 unless it really dimmed it.