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jetstream

21.8mag sky,M101 spirals

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I just got home from a trip to one of my dark sites,an adventure in itself.Needless to say one of the crowning events was seeing M101 spirals arms, faint but a great site.Many more things seen in this great sky,one of my very darkest :smiley: Going to bed,more tomorrow

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Gerry,

Sounds great but tomorrow please tell me what 21.8 mag means.

Alan

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Gerry,

Sounds great but tomorrow please tell me what 21.8 mag means.

Alan

21.8 MPSAS is the reading Gerry got from his SQM meter Alan, that gives that site limited magnitude of 6.5 which is nice and dark.

Lots of other NGC's within M101's spiral arms, a UHC filter really helps to make them stand out.

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Seeing the spiral arms of M101 for the first time is one of my fondest Astro moments. It's such an incredible sight.

For me it beats M51 hands down.

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I've managed nearly all of the NGCs in the spiral arms of M101 with my 12" at my UK dark site (which reaches 21.7 SQ). I needed a detailed image in order to identify them. Spiral arms of M101 are pretty complex and take some effort - but it's worth it.

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I love my SQM, it gives an indication of a sites potential somewhat regardless of sky transparency as long as the transparency is average or better(last night).I am not that good at NELM,but getting better and the faintest I could see was 6.2 or so.The difference being the light extinguishment from things in the air.Anyway,this site had given 21.5-21.6 mag with snow on the ground,now that its mostly gone and the summers sun is at bay it appears the site gained about a 1/4 magnitude.I took about 50 readings to warm my sensor and confirm the readings.

Well on the way up the hill I got stuck,really stuck.As any 4x4 owner knows,when you take a run at the snow drifts,mud etc you better make it through....not me! :grin: Buried,hung up the frame-snow up to my knees when I got out,mushy,terrible snow.A bit of shoveling and with the differential lock engaged I spun up the hill, fishtailing away,almost bushing it in the ditch....but I made it.Made into some a very awesome private, quarry  site

I saw so many galaxies I'm still shocked a bit sitting here with my coffee.In Virgo I had 5 galaxies the the same FOV,galaxies eveywhere,same as to the right of Leo-and then there was the Leo triplet itself,rapidly becoming a favorite of mine.M51 showed spirals and unusually took 150x with with my Delos 8mm,but the EP winner of the night was the 10mm Ethos,my best DSO EP,stark contrast-excellent.A peak at M101 revealed its spiral nature,I just was not expecting this at all,what a prize! :smiley: I actually like it better than M51 too and M101's companion galaxy was right there tagging along for the ride.Over in Coma a bunch of DSO was seen,but I kept coming back to one of them-a brightish,long,thin edge on galaxy that just held my attention.No idea what it was,until Bigmac helped me out (thanks Stu).....the Needle galaxy it was!NGC 4565,this will be another favorite.

You know all these views were fantastic,but perhaps the best view was when I stepped out of my truck,lights went out and I just stared at the sky,velvet black,diamonds gleaming everywhere.I stood there, in amazement for what seemed like a very long time

Edited by jetstream
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Gerry,

Sounds great but tomorrow please tell me what 21.8 mag means.

Alan

Alan,

As Mike explained, the SQM is a measure of sky darkness, you can do the conversion to Naked Eye Limiting Magnitude(NELM) by this link

http://www.unihedron.com/projects/darksky/NELM2BCalc.html

A 14.3 MPSAS reading in SQM means only magnitude 1 stars visible naked eyes, while 20.1 reading mean you see the brighter mag 6 stars. The difference between a 20.1 sky to a 21.8 sky is about one full magnitude, which is about difference between a 5" to 8", or 8" to 12" in scope aperture for light grasp, i.e. an 8" will work in 21.8 sky like a 12" in 20.1 sky, everything else equal.

My backyard has typical SQM reading about 18.5, which means I can only see mag 4 stars naked eyes.

Edited by YKSE
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Great session Gerry and that's good going achieving the spiral structure in M101. I will give this a try too, when I next reach dark skies. I also use 10mm on the spiral structure of M51 (x160).   

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Sounds an interesting piece of kit though I would have thought that no matter what the meter ststes 21.6 or what ever the limiting factor has to be the pupil of the eye, a younger person with good eye health will always be able to see more, unless you are bionic, like me. Alan Potts was the cheaper 600 quid man.

Alan

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 a younger person with good eye health will always be able to see more

Alan

That's absolute right, it's just over-simplied in the sentence "everything else equal".

A SQM is useful for someone looking for a darker site, do a relative comparison of darkness of different sites. or of different days, other factors like transparancy, seeing conditions are not measured.

acey's post here has much better information about SQM:

http://stargazerslounge.com/topic/214689-sqm-readings/#entry2299362

Edited by YKSE

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Sounds an interesting piece of kit though I would have thought that no matter what the meter ststes 21.6 or what ever the limiting factor has to be the pupil of the eye, a younger person with good eye health will always be able to see more, unless you are bionic, like me. Alan Potts was the cheaper 600 quid man.

Alan

Alan if you want to buy yourself a present this is it -

http://www.firstlightoptics.com/unihedron-sky-quality-meters/unihedron-sqm-l-sky-quality-meter.html

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ya know....you can see amazing pictures of galaxys, nebula, planets, starfields etc but nothing beats seeing it for real in the field.

great observation.

Neol.

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Lovey report Gerry. A good reminder that 10 inches under the right stuff is still a lethal combo, so far (hazard a guess ) locally, but out of town by a good few miles I've not managed more than about 20- 20.5 on an SQM, ( If I had one ) just going by naked eye.  As tempting as these SQM meters might be, the temptation what the same amount of money can go towards an eyepiece is more tempting at this time.  I would like one at some point, perhaps even make one, but I'd still need to calibrate it against one or something. 

Apparently an iphone has got a reosonable app to do so, not as accurate, but those things are way too fancy for me. I am not much of a gadget person, more like live in a cave with basic needs, as much a I like science and tech on paper. I suppose that is why I like manual driven Dobs too  :grin:

Edited by AlexB67
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iphones, electronics with screens of any sought and most red torches, which can be surprising glarey when your eyes have fully dark adapted are all best avoided anyhow as they trash your night vision.

For any chance of visually capturing the spiral arms in M101, I would expect a dim single led red light head torch occasionally used and a paper chart. I experienced much of this on a recent session, my eyes had become sensitive and attuned to the dark conditions when close by a bright redlight led lantern (beacon), lap tops etc were switched on, might as well have been flood lights. it was so intrusive.

Edited by scarp15
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Mark,

A nice thought but a 108 quid just to tell me its dark where I live, I think not. At the moment April is giving me the worst month I have had for clear skies since I started counting 4 years ago, last night was the 22nd and I count 5 and one that cleared at 23.00hrs which I did not count.

This winter has been poor for stable seeing as well, last year I split Sirius countless times, this year I can count them on my fingers and detail on Mars has been very poor for me. Same scopes different seeing.

Alan

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Alan,sorry to hear about the weather over there,it should clear up soon.I use my SQM to test sites at a bunch of locations,some 60 miles away some close.I am still checking other locations.Then I use Cleardarksky's forecast to see where in my area will be best for observing.Based on the transparency forecast off I go,sometimes east,sometimes North etc.Last night (22nd) I caught the tail end of a patch of better sky,which gave me the chance to view M101's sprirals again and then bag 9 galaxies in a small(.8deg) TFOV.Last nights new site should be good for a HH try coming up down the road,got to plan these things out.I think its fun finding new dark sites! :smiley:

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Good going seeing the spiral structure in M101. I spotted it a few years back with my 8", from a very dark site. The first hints of spiral structure in it was a rotation illusion as the eye moved. This is a halmark of spiral structure. Very careful use of averted vision brought out more detail

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