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Norfolk star gazer

Cigar Galaxy M82 - Bode Nebula

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I found M82 & M81 last night for the first time and was wondering how big it should look in my 10 inch dob with a 25mm EP and how much detail should I be able to see?

The conditions were very good (I have very dark skies) and I could make out the cigar shape of M82 but it was only a small line and no real detail. I tried higher magnification and it got a bit bigger, but still no detail. What's the best magnification for Nebulas?

I saw something else close by and thought it was M81 as I could see it in the viewfinder at the same time as m82, but after looking online, I think it might be NGC 3077 and I might have missed M81! The object looked like a small ball with a halo around it!

I am used to seeing the planets as the size of a lentil, so not expecting it to be huge, but was hoping that nebulas would be mostly like the Orion Nebula, but obviously understand that the distances and sizes are different.

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Hi,

I think you probably did see M81 as it is significantly brighter than NGC3077 and appears in the same field of view as M81 at low power.

M82 has higher surface brightness than 81 so I find it the more rewarding of the two. It shows some mottling in the central regions under good conditions and with good dark adaptation. Despite being called 'nebulae', these two are of course galaxies so unfortunately don't respond to filters, they just need dark skies to show their best.

There is a school of thought that viewing DSOs using an exit pupil of around 2mm gives optimum contrast. In your scope, this would be a magnification of x125 i.e. an eyepiece around 10mm. Unfortunately most people say the standard 10mm is not that great so perhaps an eyepiece upgrade would help.

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Hi, my 10mm is a basic one that came with the scope, but not that bad. I found m82 with the 25, and went to 20 and then 16 (2 x barlowed a good FOV 32mm) and various others down to a 7mm, but then tricker to find as it was a smudge. The closest I can get to a 10mm with a good FOV EP, would be if I 3 x barlowed a 27mm (9mm) or a 3 x barlowed 32mm (about 10). Would you recommend using barlows when viewing DSO or is unbarlowed best?

Otherwise it's to the shop to get a decent 9mm / 10mm!

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I found M82 & M81 last night for the first time and was wondering how big it should look in my 10 inch dob with a 25mm EP and how much detail should I be able to see?

I am used to seeing the planets as the size of a lentil, so not expecting it to be huge, but was hoping that nebulas would be mostly like the Orion Nebula, but obviously understand that the distances and sizes are different.

Would that be the size of a lentil at the end of your nose, or at arm's length? The apparent size of an astronomical object is the angle it subtends at your eye. The Orion Nebula is enormous, bigger than a full Moon when viewed at a dark site (though a lot smaller at a light polluted one). The Moon has an angular diameter of about half a degree; the angular diameter of M82 (on its long axis) is about a quarter of that. This in turn is about ten times bigger than Jupiter. So if Jupiter looks like a lentil somewhere, M82 would look like the same lentil at a tenth of the distance (assuming it to be a disc rather than cigar). M82 is large compared with most DSOs (by which I mean the 7000+ objects in the NGC). Your average galaxy is roughly Jupiter sized, though obviously a lot fainter. How much detail you can see depends on how dark your sky is: at a light-polluted site you will notice little or no detail in the majority of DSOs that you are able to see at all.

Rare exceptions include objects such as the Orion Nebula and M81. The latter can be seen as a central bulge with fainter outer disk, even at a light polluted site. M81 has an angular diameter about twice as big as that of M82. NGC 3077 is featureless. What you saw was certainly M81, a lentil looking about 20 times closer than a Jupiter-sized one, but with fuzzy edges. Light pollution would have taken away much of the edge.

When it comes to detail in galaxies you're mostly looking for the following:

Outline (how oval, circular, edge-on or irregular it is).

Brightness profile (look from edge to centre or vice versa: is there a continuous gradation of brightness, or a sudden jump, or no change?)

Size (in arcminutes rather than lentils - a rough estimate of small/medium/large).

Overall brightness (from hardly visible to eye-popping).

Anything else (e.g. dark lanes, patchiness).

Make up your own mental scale and try estimating these things roughly. William Herschel invented the idea in the 1780s and it's how all the descriptions in the NGC work (compiled a hundred years later). It makes for more informative observing notes than "wow!".

As to magnification, it depends on the object. Start low and keep increasing until there is no further gain. As Stu has mentioned, an exit pupil of 2-3mm will probably be the most "comfortable" and rewarding. Barlowing may or may not improve the view. High magnification works on DSOs at a dark site, but at a light-polluted one is likely to make them vanish. If you want a good view of a lentil you find an optimum distance at which to hold it in front of your eye. You're doing something similar with DSOs. A lentil 1mm away is very big but shows no detail at all.

Edited by acey
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Would that be the size of a lentil at the end of your nose, or at arm's length?

When it comes to detail in galaxies you're mostly looking for the following:

Outline (how oval, circular, edge-on or irregular it is).

Brightness profile (look from edge to centre or vice versa: is there a continuos gradation of brightness, or a sudden jump, or no change?)

Size (in arcminutes rather than lentils - a rough estimate of small/medium/large).

Overall brightness (from hardly visible to eye-popping).

Make up your own mental scale and try estimating these things roughly. William Herschel invented the idea in the 1780s and its how all the descriptions in the NGC work. It makes for more informative observing notes than "wow!".

Hi, thanks for the detailed explanation. It looks like I need to do some studying to fully understand what I can see any why etc. Trying to enjoy the viewing rather than how the universe works etc, but looks like I need to look into that as well.

The description of a lentil was something someone used on here when I first saw Jupiter and I asked how big should it be.

They said between a lentil and a pea, depending on magnification etc.

In answer to your question, (not having a lentil to hand) I would say that it was at arms length.

I guess that I was expecting all galaxies / nebulas to look something like Orion and going by people's comments on here about how they see spirals and lots of details (some using the same scope as me) I was wondering where I am going wrong (unless it's my eyesight).

I have dark skies here and the only light pollution is from my property, which obviously I can control

Edited by Norfolk star gazer

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To paraphrase two remarks by William Herschel:

Seeing is an art that must be learned.

Once a detail has been observed and appreciated in a large scope at high power, it may become apparent to the same observer using a smaller instrument at lower power.

Edited by acey
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NSG I used a 10 inch for years and saw 100s of galaxies with it. Most are very faint but you can still make out different shapes and textures. You can make out hints of arms and dust lanes in the brightest 20 or so.

M82 is one with vivid dark lanes. You should see these with a good 10mm eyepiece. Look at sketches online.to get a Sense of what to expect, not photographs.

Try M51 which shows some structure.

Good luck.

Mark

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Hi, my 10mm is a basic one that came with the scope, but not that bad. I found m82 with the 25, and went to 20 and then 16 (2 x barlowed a good FOV 32mm) and various others down to a 7mm, but then tricker to find as it was a smudge. The closest I can get to a 10mm with a good FOV EP, would be if I 3 x barlowed a 27mm (9mm) or a 3 x barlowed 32mm (about 10). Would you recommend using barlows when viewing DSO or is unbarlowed best?

Otherwise it's to the shop to get a decent 9mm / 10mm!

I would tend to avoid x3 barlowing for visual use as it can do awkward things with the eye relief of your eyepiece. Perhaps try an upgrade, many people do see the benefit.

BST Starguiders are often recommended, under £50 new, you buy them from an eBay shop, perfectly trustworthy. Plenty of other options out there too depending on budget

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I would try some more magnfication but not excessively so.

When I had a 10" scope and with my 12" scope now I find a good quality 8mm eyepiece really helps tease out some of the surface details of M82. The magnifications given with those scopes are 150x and 199x respectively.

The relatively high magnification darkens the background sky which helps to enhance the surface contrast of the galaxy making the dark rifts across it more clearly defined.

From my back garden I generally struggle to see much in the way of structure in galaxies even with my 12" scope. I wait until the targets are high in the sky to give myself the best chance with them.

Darker skies do contribute to helping to see the "form" of galaxies and nebulae. Filters such as the UHC and O-III also help with the latter but not with galactic targets, alas.

As with planetary viewing, the longer you observe an object, the more detail you gradually start to perceive as well.

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I would tend to avoid x3 barlowing for visual use as it can do awkward things with the eye relief of your eyepiece. Perhaps try an upgrade, many people do see the benefit.

BST Starguiders are often recommended, under £50 new, you buy them from an eBay shop, perfectly trustworthy. Plenty of other options out there too depending on budget

I have a 2 x Barlow and bought a 3 x to give me a wider range of EPs as I have some decent 25, 27 & 32 EPs.

Looks like I will have to bite the bullet and get some more eps.

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As with planetary viewing, the longer you observe an object, the more detail you gradually start to perceive as well.

I guess I was concentrating to much on trying to find the right EP and didn't give myself the chance to look at it long enough with each EP. Looks like a new 10mm might be on order soon.

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I have a 2 x Barlow and bought a 3 x to give me a wider range of EPs as I have some decent 25, 27 & 32 EPs.

Looks like I will have to bite the bullet and get some more eps.

TBH you really don't need a huge collection of eyepieces for this type of observing.

In my 10" scope I pretty much use only two eyepieces and a 2" x2 powermate (very similar to a barlow).

A 20mm 82˚ AFOV wide for low power and a 12mm 82˚ AFOV for medium, I then add the powermate for high power. 

The 20mm is wide enough for practically any object. There are some very rare occasions when I use a 31mm monster but it really isn't often, as only a handful of objects warrant such a massive FOV when using a 10" f/4.5 scope. 

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I guess I was concentrating to much on trying to find the right EP and didn't give myself the chance to look at it long enough with each EP. Looks like a new 10mm might be on order soon.

If eyerelief and narrow field of view isn't an issue the 10mm BCO could be useful, very high contrast and an excellent lunar/planetary eyepiece. This is one of my most used eyepieces.

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First off: Congratulations to you for seeing these wonderful galaxies for the first time! These are great and worthy of coming back time and time again. Echoing sentiments from the previous posts, the eye needs a lot of training at the eyepiece and with experience more detail and recognisable features will become easier and the whole experience gets more rewarding.

Hard to say what size a given object will look to you in your large dob but I think it was mentioned above to shoot for something giving about 2mm of pupil exit for galaxies. I've read 1.5mm somewhere for a high power view on galaxies like M81 which can take it, and the rules are not so hard and fast because outer eyes and preferences are different. My 7mm only provides .93mm of pupil exit but I found the view of these two galaxies last night to be very satisfactory. That could be because of the moderate light pollution here. Your choice of a replacement 10mm sounds a good one and even a modest upgrade like the BST will be a lovely addition. I've got a 12mm BST and this performs well on galaxies in my scope and also happens to give me the best results on comets at 50x. Try to plan your collection for high medium and low power EPs. As mentioned you don't need loads and a good Barlow can double the collection.

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