42 replies to this topic

[Whiteduckwagglinginspace]

Two questions about finding Planetary Nebula:

First question: how much influence has the moon on finding Planetary Nebula?

Second question: can you find Planetary Nebula without a filter?

Thanks for helping!

[tcifani]

The moon, especially a brighter and fuller moon, impairs the viewing of most deep sky objects. I generally avoid observing faint dso’s like planetary nebula unless there’s little or no moonlight.

 

Most planetary nebular are small and faint. Dark skies and higher magnifications are your friend. I currently don’t use nebula filters, except for the “gas” filter to get out of town to darker skies. 

 

Where do you live (roughly speaking) and what kind of telescope are you using?

 

Edit: also, give us a couple of examples of PN you are trying to observe. In my experience, these can be a bit tricky. M57 The Ring Nebula, for example, is small with a magnitude of 8.75 but I can easily spot in the city using a small refractor. M57 is compact but has more surface brightness. M27 The Dumbbell Nebula is actually much larger and has a lower magnitude of 7.4 but I have a difficult time even finding in the city with a 6" Dob because its surface brightness is low.

Edited by tcifani, 09 February 2025 - 07:45 PM.

[SoCalPaul]

In my experience:

 

Q1: The moon has a big impact on all DSO observing, depending of course on the phase. The bigger the phase, the badder. Some planetary nebulae are relatively bright and might still be identifiable, but given the amount of detail you lose, and the increased difficulty of finding dimmer objects, I consider it a losing proposition.

 

Q2: Yes, you can most definitely locate and observe PNs without a filter! There are many variables involved in locating and observing DSOs, some of the important ones are 1) aperture, 2) light pollution, 3) your observing skills. Many more but I think these are probably the most critical.

 

Filters can work wonders. I have a Lumicon Premium UHC filter that brings out amazing levels of detail in emission nebulae, and a Lumicon OIII filter that works well on many PNs (but not all).

 

A few suggestions:

 

First, see how well you can do without any filters. Hone your locating and observing skills.

 

Second, if there are any clubs or observing groups near you, attend an observing night and ask around. Some observers will probably have filters and might be willing to demonstrate their effect.

 

Clear skies,

Paul

[ShaulaB]

The Moon is an enemy of many deep sky object observers.

 

No mention of telescope. The larger the aperture, the easier small dim objects like planetary nebula will be to view in the eyepiece. Driving to darker skies always helps. Try observing PNs without a filter before investing in a good OIII filter.

 

No filter needed for the Ring Nebula M57 and the Dumbell Nebula M27. These are detectable in ordinary binoculars.

[Whiteduckwagglinginspace]

Thank you very much, gentleman.

I did read, that you can use high magnification on Planetary Nebula.
Therefore, I thought that these Planetary Nebulae should be bright.
Therefore, I thought that it shouldn't be a problem to find them, while the moon is shining.

But given your answers, this reasoning is incorrect.

To answer the questions:
I live in the most southern point of Norway and using a 8 inch dobsonian.
I tried to find: the Owl Nebula & the Eskimo Nebula - but didn't succeed. 

Edited by Whiteduckwagglinginspace, 09 February 2025 - 08:03 PM.

[tcifani]

Thank you very much, gentleman.

I did read, that you can use high magnification on Planetary Nebula.
Therefore, I thought that these Planetary Nebulae should be bright.
Therefore, I thought that it shouldn't be a problem to find them, while the moon is shining.

But given your answers, this reasoning is incorrect.

To answer the questions:
I live in the most southern point of Norway and using a 8 inch dobsonian.
I tried to find: the Owl Nebula & the Eskimo Nebula - but didn't succeed. 

If your skies are moderately dark or better, you should be able to view these with your 8" Dob.

 

Question: are you first using a low power wider field eyepiece to star hop to the correct location? Or are you using a high power eyepiece the entire time?

 

You should get as close as possible using a lower power eyepiece (25mm, 32mm, etc....). The Owl Nebula may only look like a dim star at low power, but you can then use higher power eyepieces to see more detail.

 

With a good transparent dark sky and at least 150x, you should be able to see shape and surface details, although these nebulas are both small.

Attached Thumbnails

• 

Edited by tcifani, 09 February 2025 - 08:15 PM.

[Whiteduckwagglinginspace]

According to a light-pollution map, I live at bortle 3. Maybe bortle don't always say so much, but I can confirm that there is very little light-pollution over here and very dark skies.

I use a 25 mm as an searching-eyepiece, which gives 48X magnification.
So, this owl nebula is only as big as a dim star at this magnification?
This should explain why I don't find it. I expected it to be larger than the stars at this magnification. Next to this, it will be difficult to pick the right dim star, between all the other dim stars. 

Edited by Whiteduckwagglinginspace, 09 February 2025 - 08:36 PM.

[Tony Flanders]

Thank you very much, gentleman.

I did read, that you can use high magnification on Planetary Nebula.
Therefore, I thought that these Planetary Nebulae should be bright.
Therefore, I thought that it shouldn't be a problem to find them, while the moon is shining.

But given your answers, this reasoning is incorrect.

To answer the questions:
I live in the most southern point of Norway and using a 8 inch dobsonian.
I tried to find: the Owl Nebula & the Eskimo Nebula - but didn't succeed. 

Planetary nebulae are all over the place, from ones that are so concentrated that they're hard to distinguish from stars to ones that are so diffuse that they're barely visible under pristine dark skies even with a filter.

 

Both M97 (sometimes called the Owl Nebula) and NGC 2392 (sometimes called the Eskimo Nebula) are both between those extremes, but NGC 2392 is definitely toward the concentrated end of the spectrum, and therefore readily visible without a filter at full Moon if you know exactly where to look. It's listed at magnitude 10.1, which isn't terribly bright, but it's just 48 arcseconds across, giving it an outrageously high surface brightness.

 

M97 is listed at magnitude 9.9, giving it a slightly greater total brightness than NGC 2392. But it's 3.3 arcminutes across -- four times the diameter of NGC 2392, and sixteen times the area. So its surface brightness is much, much fainter. It's challenging to locate even on a moonless night, with a filter, from a bright suburban sky.

 

M57 (the Ring) is also quite intense, though not as much as NGC 2392, and M27 (the Dumbbell) is medium in surface brightness, but pretty easy to see nonetheless because of its immensely great total brightness.

[tcifani]

It sounds like you are doing all the right things, and have nice dark skies.

 

Look at the second and third image on this web page - only imagine M97 a little more dim and without color, since these are astrophotos.

 

https://www.astronom...021/01/17/m097/

 

At just under 3' (arc minutes), The Owl Nebula is small but not so small that it would be confused with a dim star at higher magnifications. It may look like a dim fuzzy disk at first. Are you familiar with using adverted vision when viewing faint objects?

 

EDIT: "averted vision", not "adverted vision" (kindly pointed out to me).

Edited by tcifani, 10 February 2025 - 02:12 PM.

[WillR]

If you are only using 48x that may be the problem. Many of these are quite small. I agree with Tony that NGC 2392, the Eskimo, is much brighter than M97, the Owl. Some of the small ones can be hard to tell from stars at low magnification. I know have a filter wheel I can use on my dob, enabling me to switch back and forth from no filter to an Oiii. That is a big help in determining if I am looking at a PN.

[Whiteduckwagglinginspace]

It sounds like you are doing all the right things, and have nice dark skies.

 

Look at the second and third image on this web page - only imagine M97 a little more dim and without color, since these are astrophotos.

 

https://www.astronom...021/01/17/m097/

 

At just under 3' (arc minutes), The Owl Nebula is small but not so small that it would be confused with a dim star at higher magnifications. It may look like a dim fuzzy disk at first. Are you familiar with using adverted vision when viewing faint objects?

Yes, I'm familiar with adverted vision. Most of the times I see faint objects first by looking next to the object. If I'm right (looking at the pictures), the Owl Nebula is a bit bigger than the surrounding stars, when using a low (searching) magnification(?)

[ram812]

Hello! You make take a look at CN's "Sketching" forum for sketches that are done with instruments 8" or larger. That should give you a good idea of some of the faint structures of the PN's you might view. I find them vary similar to what I see through the eyepiece of my 10" Reflector.

Good hunting!
Clear skies, Ralph
So. Oregon

[Whiteduckwagglinginspace]

If you are only using 48x that may be the problem. Many of these are quite small. I agree with Tony that NGC 2392, the Eskimo, is much brighter than M97, the Owl. Some of the small ones can be hard to tell from stars at low magnification. I know have a filter wheel I can use on my dob, enabling me to switch back and forth from no filter to an Oiii. That is a big help in determining if I am looking at a PN.

Thank you for your advice!

So, you recommand using a bigger (searching) magnification than 48X. What kind of magnification do you think about for finding planetary nebula?

I have no filterwheel, but I have a UHC-filter. Reading your words, this will help me to distinguish the stars from the planetaries a bit easier.

[gnowellsct]

Two questions about finding Planetary Nebula:

First question: how much influence has the moon on finding Planetary Nebula?

Second question: can you find Planetary Nebula without a filter?

Thanks for helping!

I took out a c14 on a big massive go-to mount with the idea of testing the go-to protocols on bright DSOs. This was during a full moon. You couldn't see any DSO of any kind. M57 and m27 you say heck I can see those from Manhattan and maybe you can. But I couldn't see them on this field with the full moon high in the sky.

[HalfEazy]

I think the moon has a huge effect on most visual observations of DSO.

 

Moon is currently really bright and is not mixing well with light pollution in my area

[WillR]

Thank you for your advice!

So, you recommand using a bigger (searching) magnification than 48X. What kind of magnification do you think about for finding planetary nebula?

I have no filterwheel, but I have a UHC-filter. Reading your words, this will help me to distinguish the stars from the planetaries a bit easier.

Magnification depends on the particular planetary. It really depends on the size. A good one to find is the Cat's Eye nebula or NGC 6543 in Draco. This one is particulary bright, but only 16" across at the core. It would be a tiny disc at 48x, so I would up the power to 100-150x. Or even higher once you know you are on it.

 

Are you star hopping? Do you have a finder on your dob, or are you just using the 25mm in the scope as a finder? 48x would mean a very small FOV for a finder, so finding small things would be difficult. If you are going to star hop, I would get a finder scope. I use a laser to get in the area and a 10 x 50 RACI finder to star hop to the target.

[Jay_Reynolds_Freeman]

It is not clear whether your wish to locate planetary nebulae without a filter is because you find that an interesting challenge, or for some other reason. If that is how you want to do it, that's fine -- I myself like challenges. But just in case, let's make sure you understand that using the right kind of filter makes finding planetary nebulae very easy.

 

What you would do is use a filter that passes the green line of ionized oxygen that has a wavelength of 500.7 nanometers, and not much else. Most planetary nebulae emit much of their light at that specific wavelength. Get one of these filters in two-inch size -- 50.8 mm -- and use an eyepiece with enough eye relief that you can easily pass the filter back and forth between your observing eye and the eyepiece. When you do that, all the stars in the field will become much dimmer, since the filter is absorbing most of their light, but the planetary will be almost as bright with the filter present as when the filter is absent, and by moving the filter in and out of the optical path rapidly it will be very obvious whether a planetary nebula is present -- the stars will appear to blink on and off, but the light from the planetary will be nearly steady.

 

If you use this technique with a low-magnification wide-field eyepiece, you will be scanning a large area of sky all at once, and you will be able to identify planetaries even if their apparent size is so small that they look like stars. Once a planetary is identified, you can center it and increase magnification to look for detail. The filter may help then: Try it and see what you like.

 

Clear sky ..,

[Whiteduckwagglinginspace]

Are you star hopping? Do you have a finder on your dob, or are you just using the 25mm in the scope as a finder? 48x would mean a very small FOV for a finder, so finding small things would be difficult. If you are going to star hop, I would get a finder scope. I use a laser to get in the area and a 10 x 50 RACI finder to star hop to the target.

I have a Celestron Starsense 8 inch dobsonian. Most of the times, the Starsense app can't find position and doesn't work at all. Followed all the problemfixing tips from Celestron, but still nothing. Strange enough, I'm one of the few people having problems with the app.
At the moment, I try AtroHopper and hope this will work better, but I can say allready that I don't like the layout. Terrible colouring and very unclear. Also, working with the very little green arrow is a pain in the butt. I didn't need glasses with the Starsense app, but I absolutely need them with AstroHopper. 

Personally, I also want to learn to find the objects in the sky by hand and my own mind. At first, I look at Stellarium on my laptop to locate where it is, looking at the constellations / stars. Of course, with the moon the smaller stars disappears and this makes it more difficult. I have no finder scope, but I have a red dot finder. After using this, I use the 25 mm eyepiece.  

[tcifani]

Wow! WillR hit the nail on the head with his question on star hopping and using a proper finder scope. And I don’t believe you are the first to have problems with the Starsense app, so don’t be hard on yourself. Learning how to find objects in the night sky takes time and patience. It’s like driving a car to an unknown destination without using a GPS system but relying on good old fashioned paper map and your own visual ability. Once you learn how to locate objects by star hopping, you’ll have gained a skill that can never be replaced. All you need is a good map of the sky, your eyes, and your fingers to work like pointers.

 

Star hopping is a process for locating objects in the sky that uses simple geometry by framing brighter objects and forming imaginary patterns. I would start out with a few easier brighter objects, even if you’ve already seen them. M3 and M37 are good examples right now. M1 is a little more of a challenge, but worth the effort.

 

In all three of these examples, I look for the brighter stars, like Arcturus and Rho Boötis in the constellation Boötes, and in my mind I see a perfect equilateral triangle between the two brighter stars and M3. Do this first without a telescope or finder, just looking up at the night sky without optical aid. With your arms extended out in front of you, use your fingers to help visualize these imaginary shapes. I like to spread my thumb and forefinger out to make a sort of ruler to create imaginary units that I can count if needed.

 

Then, try pointing your scope in this direction and locating the object. Since you only have a red dot finder, that’s ok for now. I highly recommend a RACI finder like WillR mentioned for dimmer objects. A pair of binoculars can be very useful as well to help star hop and locate objects.

 

Here's a good free downloadable paper map that you can print out yourself and mark up if necessary. There's nothing wrong with electronic sky maps and phone apps, but I still print paper maps because I like to mark them up and make notes.

 

https://www.deepskyw...psky-atlas.html

 

Good luck!

Attached Thumbnails

• 
• 
• 

[EsaT]

According to a light-pollution map, I live at bortle 3. Maybe bortle don't always say so much, but I can confirm that there is very little light-pollution over here and very dark skies.

I use a 25 mm as an searching-eyepiece, which gives 48X magnification.
So, this owl nebula is only as big as a dim star at this magnification?
This should explain why I don't find it. I expected it to be larger than the stars at this magnification. Next to this, it will be difficult to pick the right dim star, between all the other dim stars. 

Bortle 3 is better than what I have, so M97 should definitely be visible.

Though that value is for zenith and lower target might hit light dome of some nearby city/town.

But still can't say anything good about development of light pollution here and you propably also don't have much snow to increase it.

 

Anyway that narrow view 25mm Plössl isn't good for ~1200mm focal length telescope because of narrow AFOV making for narrow view.

Celestron just bundles it because it's no doubt dirt cheap in volumes factory buys them and fools buyers into thinking they get something of value.

Actual wide view giving eyepiece would make both M97 and M108 easy to find starting from Merak:

https://wp.uni-olden...major-deep-sky/

 

Though they aren't visually big targets.

But still far bigger than M57, which at low magnification looks precisely just like bloated star...

So once you know how to locate M57, it's just best to go straight for 100+x magnification. Actually even toward 200x is fine at least in 10" Dobson.

 

M101 in Ursa Major is the harder target because of low surface brightness, but in Bortle 3 it should be well visible.

Though once again wide view eyepiece would be good start for finding it.

But can see hint of it also in 8x50 finder.

 

 

 

IPersonally, I also want to learn to find the objects in the sky by hand and my own mind.

Rigel Quickfinder/Telrad and RACI finder would be the best combination:

 

Unlike with "meh dot" finder those give you guide circles to help measure/estimate distances.

And if stars needed for star hopping are out of reach of naked eye, finder scope collects more light than eye and magnifies image.

Actually 50mm finder would show many targets under dark sky.

[Dave Mitsky]

Small planetary nebulae that are prominent in terms of surface brightness such as NGC 2392, NGC 3242, NGC 6543, NGC 6572, NGC 7009, and NGC 7662 stand up well to light pollution.  Using the nebula filter blinking technique that Jay Reynolds Freeman described can identify them and additional magnification can then be applied.

[Dave Mitsky]

Star hops to the objects that I listed above and several others can be found at https://www.skyledge...opping-list.htm by inserting planetary nebula into the search function.

Here's a link to the one for NGC 2392. 

 

https://www.skyledge...NGC2392-hop.htm

 

 

[Starman1]

Two questions about finding Planetary Nebula:

First question: how much influence has the moon on finding Planetary Nebula?

Second question: can you find Planetary Nebula without a filter?

Thanks for helping!

Planetary nebulae are typically small, and reasonably bright, but like all DSOs get killed by moonlight.

If you don't stay up past midnight, look when there is no moon in the sky, like from last quarter phase to a couple nights past new moon.

 

Some general rules about viewing any DSO:

1) Don't even bother looking for these faint objects when the Moon is above the horizon.  Wait till after moonset or observe before moon rise.  When the Moon is up, observe the Moon.
2) Be dark adapted--that means 30-45 minutes outside away from lights before you start going for faint objects.
3) Don't bother if there are many clouds in the sky because the uncloudy part of the sky is still hazy.  The only exception is if the clouds are only on the horizon.
4) Start at low power until you identify the field, then increase the power until the object is visible.  You will probably find magnifications of 60x+ most useful for DSOs.  Remember, the image gets larger with magnification but also gets dimmer.
5) Don't look for objects until it is completely dark.  The sun must be 18° below the horizon (90 minutes after sunset at 40° North).
6) Due to the atmosphere dimming objects when it gets thick, try to confine your observing of faint objects to near the N-S meridian, the imaginary line from due north to due south that passes through the zenith, where objects are highest in the sky.
Avoid looking at faint objects below about 30° off the horizon unless the object is in the deep south and never rises above 30°.  The difference in how the Orion Nebula appears when it just clears the trees and when it is high in the sky is quite profound.
7) Use averted vision.  Instead of looking directly at the object, look 15° toward the side (to the right side for right eye, left for left) and let the area of the retina most sensitive to light see it first.
If it's bright enough you can then look at it with direct vision.  Some objects will only be seen well with averted vision.
8) sit down to observe.  We are not stable when standing (your head is always moving) and you will get tired faster.
9) Make plans to move to darker skies once in a while during the New Moon so you can see what the scope is capable of in a darker sky.  Contact your nearest astronomy club to find out where they go to see darker skies.

[Starman1]

It is not clear whether your wish to locate planetary nebulae without a filter is because you find that an interesting challenge, or for some other reason. If that is how you want to do it, that's fine -- I myself like challenges. But just in case, let's make sure you understand that using the right kind of filter makes finding planetary nebulae very easy.

 

What you would do is use a filter that passes the green line of ionized oxygen that has a wavelength of 500.7 nanometers, and not much else. Most planetary nebulae emit much of their light at that specific wavelength. Get one of these filters in two-inch size -- 50.8 mm -- and use an eyepiece with enough eye relief that you can easily pass the filter back and forth between your observing eye and the eyepiece. When you do that, all the stars in the field will become much dimmer, since the filter is absorbing most of their light, but the planetary will be almost as bright with the filter present as when the filter is absent, and by moving the filter in and out of the optical path rapidly it will be very obvious whether a planetary nebula is present -- the stars will appear to blink on and off, but the light from the planetary will be nearly steady.

 

If you use this technique with a low-magnification wide-field eyepiece, you will be scanning a large area of sky all at once, and you will be able to identify planetaries even if their apparent size is so small that they look like stars. Once a planetary is identified, you can center it and increase magnification to look for detail. The filter may help then: Try it and see what you like.

 

Clear sky ..,

For visual use, you need to pass BOTH lines of Oxygen III, one at 495.9nm and the other at 500.7nm.

When only the 500.7nm line is passed, you lose 25% of the O-III energy and make the object dimmer.

The rest of your post is excellent advice.

[Starman1]

Thank you for your advice!

So, you recommend using a bigger (searching) magnification than 48X. What kind of magnification do you think about for finding planetary nebula?

I have no filterwheel, but I have a UHC-filter. Reading your words, this will help me to distinguish the stars from the planetaries a bit easier.

The UHC filter should help, because it does pass both O-III lines in the spectrum.

So the likelihood is that between local light pollution and the moonlight, the nebulae were rendered dim enough to escape notice.

Try again when there is no moon.

An 8" scope can see hundreds, if not >1000 planetary nebulae.

I would suggest, if it has a wide enough field of view to be used as a finder, using an eyepiece of at least 10x/inch of magnification with the UHC filter attached.

The planetaries should be fairly obvious, if small.  The UHC filter won't be of much use to improve contrast above about 12.7x/inch of aperture, and you'll find magnifications of 150x much better at revealing planetaries.

There are exceptions, such as:

M27, which you'll find excellent as low as 100x

NGC7293, the Helix nebula, best at lower power, like 50x

NGC246, the skull nebulae, also best at lower magnification

All the above significantly easier to see with a filter.

M57, the Ring Nebula, where a filter doesn't help much, but high power does,

 

Don't be afraid to use 200x in an 8" to look at planetaries, but definitely be dark adapted when you do, and shielded from any local lighting.