What aperture to see spiral arms in galaxies?

[Jim Smith]

If I wanted to make out the spiral arms in a galaxy or two from my Bortle 4 garden on a night of good seeing, what aperture 'scope would I need?

Thanks, Jim

[John]

I've seen spiral structure in M51 from my bortle 5 back garden with a 10 inch aperture on a dark night of good transparency. Not really "in your face" but it was there when my eye had adjusted and I had become fully dark adapted and I used some averted vision techniques. Subtle to be honest with you. I observed the same target with a 20 inch aperture from a darkish site a few years back and the view was like the images you see - wow !!!

It is difficult to guarantee what aperture will do this because observing conditions, observer experience and other factors have quite a bearing on what can actually be seen. 

Some observers have seen spiral structure with as little as 4 inches of aperture but not me, alas 🙄

[bosun21]

I have managed to see indications of the spiral arms with averted vision with an 8” dobsonian in bortle 5-6 skies. I can see them more clearly in my 12” on nights of very good seeing and transparency. I also found that a black sheet of fabric draped over my head eliminating all traces of stray light and being totally dark adapted is a must. The longer time spent observing at the eyepiece also helps draw out faint details.

[Guest]

I live under bortle 4 skies and have 10 and 16 inch dobs.   They key to seeing arms in skies like ours is having good clear and stable skies.  A couple weeks ago i was looking at the Whirlpool in the 16, no matter what i did I could not get a really good image.  Why.... Because it stormed earlier in the afternoon and the skies were still stirred up.  There was one time with the 10 inch i was looking right at it and while there was no definition I could see the arms.... Sort of, but again the skies were not perfect.  As has been suggested above there is no "number of inches", its all about the sky.  So if it were me and i was starting over in my skies i would get a 12 inch dob and that would get you a good shot at achieving what you want. 

[Zermelo]

I am mid Bortle 4 (SQM 21.02 is the best I've measured).
With a 6" on the best nights, I've seen the cores of M51/NGC5195 and some light patches where the arms would be, but no continuous arms. I think I would see them if my eyes were 30 years younger.
But I did see definite arms on M51 when I viewed it with a 5" Mak from a Bortle 3 site.

[Carbon Brush]

@Zermelo has raised an important point.
As we age our ability to discern detail at low light level declines considerably.
I was told by an optician that by age 60 we have 1/3 the night vision of age 20.
So aperture will brighten an object to help compensate for old eyes.

 

[josefk]

5 minutes ago, Carbon Brush said:

@Zermelo has raised an important point.
As we age our ability to discern detail at low light level declines considerably.
I was told by an optician that by age 60 we have 1/3 the night vision of age 20.
So aperture will brighten an object to help compensate for old eyes.

 

just about coincident with when you can't hump aperture about anymore 😞

• NV?
• retire somewhere dark?
• gym membership?

 

[John]

55 minutes ago, Carbon Brush said:

@Zermelo has raised an important point.
As we age our ability to discern detail at low light level declines considerably.
I was told by an optician that by age 60 we have 1/3 the night vision of age 20.
So aperture will brighten an object to help compensate for old eyes.

 

The irony there is that it is often later in life that one can afford good quality equipment with high potential performance. I quite often wonder what I would have been able to achieve if I could have afforded the equipment that I have now back in my 20's 🙄

Back then though full time work plus bringing up children would have left me too exhausted to take advantage of it so probably no overall gain then !

 

Edited August 3, 2023 by John

[Cosmic Geoff]

14 hours ago, Jim Smith said:

f I wanted to make out the spiral arms in a galaxy or two from my Bortle 4 garden on a night of good seeing, what aperture 'scope would I need?

 

A case where a camera will reveal far more than the eye. From my Bortle 6 location I have secured many images with a 4" refractor that show spiral arms in galaxies.

[John]

3 minutes ago, Cosmic Geoff said:

A case where a camera will reveal far more than the eye. From my Bortle 6 location I have secured many images with a 4" refractor that show spiral arms in galaxies.

Fair point of course but I will never forget the thrill of seeing the spiral structure and "bridge" of M51 with a 12 inch dob (not mine) and my own eye at my first SGL star party in Herefordshire 🙂

Stuff like that stays with you 😁

 

[DirkSteele]

Had an incredible view of M51 through a 6” dobsonian scope at AstroCamp back in April (Bortle 4). Spiral arms and bridge between the galaxies was readily available to observe. One of the best views of this galaxy I have ever had in a scope of this size.

[Jim Smith]

Thanks for all of the comments. I'm thinking that with my 67 year old eyes, a 12" Dobsonian might give me a chance on a good night!

[Guest]

The only "issue" with a 12 inch is its size.  Before you order one think about how you intend to move it around.  Are you going to be taking it elsewhere, will it fit in my car.  You can by straps that go around the OTA to make lifting it easier. Then you have all the other neat little things you can do to it.  Better primary springs, thumbscrews for the secondary and probably some form of dew control whether that is passive or active depends on where you live 

[Jim Smith]

8 hours ago, Mike Q said:

The only "issue" with a 12 inch is its size.  Before you order one think about how you intend to move it around. 

Yes, I was a bit worried about the size.
Perhaps an Explore Scientific Ultra Light 12" Dobsonian Telescope Gen II would be more manageable than most.

[Guest]

38 minutes ago, Jim Smith said:

Yes, I was a bit worried about the size.
Perhaps an Explore Scientific Ultra Light 12" Dobsonian Telescope Gen II would be more manageable than most.

Just answer a couple questions.  Where are you storing this thing?  In a garage, in the house and are there stairs involved?  If you are keeping it in the garage, buy or make a cart for it and leave it out there.  If you keep it in the house... That's a whole different ball of wax.  Dakota Starry Nights on YouTube has a couple videos on the ES scope, they use the 16 inch version but i cant imagine it being to much different then the 12 inch. 

[AstralFields]

The 12" is a beast. It takes considerable planning for logistics. I am planning on buying the SW 12" Classic in the future. It can fit in my car with backseat collapsed. I plan to put some wheels on the base like I did for my 8" and then just cart it from the cellar to the car in the garage.

The OTA is actually lighter! than the flex tube version, that is why I am going with the classic. 

The base is 65cm wide, which is just enough to pass my cellar door which is 70cm.

I have also tested the height of my observing chair with the height of the 12" eyepiece. 

Anyone thinking about the 12" should have experience with an 8" and then plan in detail how they are going to use the 12" exactly and if it will require a new observing chair. Otherwise there is real danger it may end up catching dust somewhere for months, being used only a couple of times per year. This seems to happen quite often even with smaller telescopes.

edit: As for M51 , I saw them in the spring.. but it was only with averted vision and very faint. They say that galaxies come alive at 16" .. and I think that is pretty much true + dark skies.

Edited August 4, 2023 by AstralFields

[Carbon Brush]

I have owned, or still own, 8", 10" and 12" reflectors.
The handling change from 10" to 12" is far more than you might think for 2" of mirror.

I would invite you to visit and have a go at moving my 12" dob, but you are a long way away.
Is there anyone nearer who might offer?

 

[bosun21]

I’m about 80 miles from you in Oxford. If you want to you’re welcome to come and see the 12” dobsonian and try it for weight etc yourself. It’s a large scope for sure.

[bish]

Had a hint of them in m51 with my old 8". Easier in my 10" and getting good in a 12". All from bortle 3. Had a quick glimpse before clouds hit in a 18". Obviously great in that! Not sure how good my eyes are.

[John]

If you can find one, an Orion Optics (UK) 12 inch dob weighs about the same as a chinese (eg: Skywatcher, Bresser, GSO) 10 inch dob. 

Edited August 4, 2023 by John

[Mandy D]

For information purposes, my new Skywatcher 300PDS OTA, complete with rings and a Losmandy dovetail was weighed at RVO and tipped the scales at 26 kg.

[John]

11 minutes ago, Mandy D said:

For information purposes, my new Skywatcher 300PDS OTA, complete with rings and a Losmandy dovetail was weighed at RVO and tipped the scales at 26 kg.

My old Orion Optics F/5.3 OTA, similarly equipped, weighed around 17kg.

[Mandy D]

1 minute ago, John said:

My old Orion Optics F/5.3 OTA, similarly equipped, weighed around 17kg.

I was, honestly, very surprised at the weight of the 300PDS. I'm used to being able to pick up any of my existing OTAs with one hand, even the 250PX, but this one is a whole new ball game. The 300PDS is f/4.9, so ought to be lighter!

[bosun21]

55 minutes ago, Mandy D said:

For information purposes, my new Skywatcher 300PDS OTA, complete with rings and a Losmandy dovetail was weighed at RVO and tipped the scales at 26 kg.

That’s heavy. My 300mm dobsonian tube is 19kg but that’s without any rings or Losmandy dovetail of course.

[bosun21]

48 minutes ago, Mandy D said:

I was, honestly, very surprised at the weight of the 300PDS. I'm used to being able to pick up any of my existing OTAs with one hand, even the 250PX, but this one is a whole new ball game. The 300PDS is f/4.9, so ought to be lighter!

Why would the 300PDS be lighter? It’s 300mm longer  and 50mm wider 🤔.

Edited August 4, 2023 by bosun21