mag 5.25 skies but very little in terms of nebulosity...

[pipnina]

Tonight at wembury I managed to spot the double star 30UMA which is mag 5.25. The dimmest I've ever been able to see. But despite this, I failed to see much in the way of galaxies or nebulae...

I got M31 and M42 in the bag very easily, but M31 seemed a little less impressive than normal. More grey and I couldn't see the first major dust lane like I'd been able to previously despite the galaxy being closer to the zenith.

I also failed to see M1, the Wizard nebula and M81/82. I think M82 was more to do with me not being able to find the patch of sky they're in but the other two slightly surprised me...

I failed at the flame, although I coulda swore I saw hints of it at one point. I'm wondering if my EPs uncoated optics and light scatter ruined my chances there... Alnitak's glare covered a lot of the EPs FOV.

Something that I think makes it more difficult for me is that I can't adjust to the inverted FOV of my scope. I have a strange feeling that with M1 I might have been looking on the wrong side of the star, although I think I could tell what side of alnitak the flame was on (which may suggest that it was visible, if only slightly).

Could haze be an issue? I notice when pulling into the car park that I see light rays coming from the headlamps (as though sunlight were passing through a window and there was dust in the room). This happens at all of my sessions... Would moving away from the sea help?

I honestly thought I'd be seeing more with mag 5.25 skies... Perhaps I'm wrong though? It's strange seeing so many stars but so little nebulosity.

    ~pip

[ronin]

M1 is both small and dim, if you read Charles Messiers original notes he found it by accident, he happened to be looking at the area for possible comets and it turned up in his view. Have sort of half seen it in a 6", I think I did other person thought it was wishful thinking when they looked. May try a 16" on it soon if I get the oppurtunity.

M82 and M81 are also dimmer then you may expect. I was setting up Stellarium a couple of nights back and I think I set DSO's to mag 6 and they 82/81 disappeared from the screen so they are dimmer then a mag 5.25 sky. I was setting Stellarium up to display the brighter objects to make a lidt of. I did not really expect M81/82 to disappear off the screen so early.

Try setting similar if you have Stellarium on your PC/laptop.

Flame nebula if I recall is odd regarding the magnitude. Some give the magnitude as if bright, others give very dim.

If it is the one I am thinking of some measure the magnitude including Alnitak - which makes it bright, mag 2 I think.

Others measure it without Alnitak and it then comes out very dim, mag 11 (maybe 9) I think.

I might have the wrong nebula and star but sort of 80% sure that it is these 2.

[pipnina]

M1 is both small and dim, if you read Charles Messiers original notes he found it by accident, he happened to be looking at the area for possible comets and it turned up in his view. Have sort of half seen it in a 6", I think I did other person thought it was wishful thinking when they looked. May try a 16" on it soon if I get the oppurtunity.

M82 and M81 are also dimmer then you may expect. I was setting up Stellarium a couple of nights back and I think I set DSO's to mag 6 and they 82/81 disappeared from the screen so they are dimmer then a mag 5.25 sky. I was setting Stellarium up to display the brighter objects to make a lidt of. I did not really expect M81/82 to disappear off the screen so early.

Try setting similar if you have Stellarium on your PC/laptop.

Flame nebula if I recall is odd regarding the magnitude. Some give the magnitude as if bright, others give very dim.

If it is the one I am thinking of some measure the magnitude including Alnitak - which makes it bright, mag 2 I think.

Others measure it without Alnitak and it then comes out very dim, mag 11 (maybe 9) I think.

I might have the wrong nebula and star but sort of 80% sure that it is these 2.

Yeah, I think stellarium includes alnitak in the measurements for NGC 2024. If you compare the brightness (in magnitude/size) to orion, flame is twice as bright as M42 according to stellarium! Deffo not true since M42 always jumps out at you, even at 0.75 exit pupil when observing the trapezium...

It could be possible I need to try and find some more experianced star gazers to observe with... Or just to get somewhere darker still (just past postbridge looks pretty neat). (Although I still feel I would have seen flame if it weren't for alnitak's glare, stars seem to get 100x brighter in the EP)

[Stu]

Under mag 5.25 skies you should be able to see M81 and M82 quite easily so I suspect this was more of a finding issue.

M1 can be a tricky customer, but again should have been visible, although if your transparency was poor that may not have helped.

The Flame is a hard target at mag 10, you are likely to struggle with this unless under much darker skies I think. I'm not sure where the info about it being twice as bright as M42 comes from but this is wrong.

The Flame is mag 10 and 30 x 30 arc minutes, M42 is mag 4 and 85 x 60 arc minutes, far brighter. Surface brightness for the Flame looks like about 17, for M42 it is 13, again making it much easier to see.

Observing with more experienced people is a good idea, but I think you need to pick your targets more carefully perhaps and not chase objects that are a challenge even under darker skies with larger instruments eg the Flame

[jetstream]

Great that you got out Pip!

Great advice from Stu, as usual!

NELM 5.25 is not all that dark really, this was similar to my home in town, but M81/M82 were visible under transparent conditions. For sure you can see them. M42 is the brightest neb viewable I think, the Flame is much much fainter. You need darker and more transparent skies for this one.

I may have asked before...what scope and eyepieces are you using?your 130mm? If you try viewing faint nebula near a bright star (Alnitak) you need a low scatter eyepiece and a narrowish FOV helps too (IMHO). Under VG skies my 90mm shows the Flame well.

You know I just viewed the Eskimos neb again and is a fantastic object, easy to find and easy to see- have you tried this one? M97 will show its eyes nicely once you figure out what the object wants to reveal them... Keep up the good work Pip!

[acey]

Simbad gives the V-magnitude of 30 Ursae majoris (aka phi UMa) as 4.56. If that was at your threshold of visibility then it's no surprise that you struggled with DSOs, though objects such as M81/82 should be visible even under those conditions.

http://simbad.u-strasbg.fr/simbad/sim-id?Ident=*+phi+UMa&radius.unit=arcmin&Radius=2

If your limit were 5.25 mag then you would possibly be able to see part of the Milky Way, and DSOs would be a lot easier, though this is still quite a way from a truly dark sky, with a limit of around 6. The logarithmic magnitude scale can be deceptive: a difference of three quarters might not sound much, but a 5.25 mag star is twice as bright as one of magnitude 6, and a 4.5 mag star is twice as bright as one of magnitude 5.25.

Some DSOs can be viewed even in a light-polluted sky with a limit of 4.5; I've managed the Crab Nebula under those conditions, though it was very faint. Shielding your eyes from ambient light can help. In this case it sounds like poor transparency might have been the main issue rather than light pollution, in which case wait for a clearer night.

[ollypenrice]

I've a feeling that certain kinds of haze damage our DSO chances not so much by obscuring the incident light as by raising the background brightness by diffusing LP. My hunch is that low lying haze is very good at this since it is ideally placed to diffuse LP. If this hunch is correct then the effect on bright sources is not so harmful but on faint ones it's a disaster.

I only float this as an idea. It may be entirely incorrect.

Olly

[Stu]

acey is correct (of course [emoji3][emoji106]). Just checked on SkySafari and 30UMa is a double, one component is mag +5.39 but the brighter one is mag +4.55 which is the one you will have seen. Is this really the dimmest you've seen? I ask because I live close to London and this is possible from my back garden so I'm sure you can access darker skies where you are? Well worth finding them

[laudropb]

I think it might just have been a seeing problem. I can find M81 and M82 from my skies which are nearer mag 5, but only when the seeing is good. I also use a 200mm Dob, which probably helps.

[acey]

I've a feeling that certain kinds of haze damage our DSO chances not so much by obscuring the incident light as by raising the background brightness by diffusing LP. My hunch is that low lying haze is very good at this since it is ideally placed to diffuse LP. If this hunch is correct then the effect on bright sources is not so harmful but on faint ones it's a disaster.

I only float this as an idea. It may be entirely incorrect.

Olly

I think you're right. At a dark site on a hazy night, if attempting DSO viewing at all, I reckon it's best to concentrate on targets that are overhead (or nearly so). Not only are you looking through less haze, but you should have a darker sky background. This is assuming that the haze is high: it's possible to find yourself surrounded by mist that only extends a few metres above ground level.

[Peter Drew]

I share Olly's "hunch" (that's why we can both be upright people ) I believe that the general decline in transparency is due to pollutants allowing the Sun, even when below the horizon, to still light up the atmosphere. 

[acey]

I share Olly's "hunch" (that's why we can both be upright people ) I believe that the general decline in transparency is due to pollutants allowing the Sun, even when below the horizon, to still light up the atmosphere.

I would disagree with that. It's man-made light-pollution that accounts for most or all of the glow of haze, certainly if the Sun is far enough below horizon for lights to be on. At a truly dark site clouds are completely black - you don't know they're there except for dark holes where stars should be. At most sites you can see clouds, because they're being lit by human lights, possibly many miles away over the horizon.

[ollypenrice]

I think you're right. At a dark site on a hazy night, if attempting DSO viewing at all, I reckon it's best to concentrate on targets that are overhead (or nearly so). Not only are you looking through less haze, but you should have a darker sky background. This is assuming that the haze is high: it's possible to find yourself surrounded by mist that only extends a few metres above ground level.

We are often attacked from below here when temperature inversions create valley mists lower down. As they build they tend to rise till they lap around our ankles and sometimes drown us. It can be very frustrating to think that being ten feet higher would have us out of it! For all that, this only happens in the small hours not too long before twighlight when it happens at all.

Olly

[pipnina]

Cheers for the help guys. Yeah I'm fairly certain I couldn't see M81/82 mainly due to getting lost... But it's possible it was beyond my transparency/sky brightness.

Hmm, stellarium lies about 30UMA then... I had thought I saw dimmer stars but trusted the computer. Thinking about it, last time I evaluated my skies to be around mag 5.2 it was when i was seeing a star (that turned out to be a double) flcikering on the edge of visibility (though it was nowhere near ursa major)

I could see 49 ori. Which is mag 4.7 (and was on the edge of visibility, though nowhere near the zenith)...

But now, going back to stellarium... I think I may have just been looking in the wrong place. My star charts don't list the location of the wizard neb very precicely so I was guessing... Turns out it was 1/2 FOVs above where I was pointing!

Similar situation with M1, I thought it was just above Alnath but it was actually by 123Tau! Again, an issue with me reading my star charts incorrectly... There may be hope yet for these objects!

Also, I use the standard SkyWatcher 25mm plossl. Which gives me 3.6mm exit pupil (which i feel is a tad low for using my OIII filter). I notice that it has no anti-reflective coatings, has very high sharpness loss towards the edge and produces a sort of halo around bright objects (looking through it at my bedroom lights showed this very well)(i'll get a picture after dinner) I will try for the eskimo... it was on my list but I never actually attempted it for some reason...

[pipnina]

I finally got the images of my EP, wondering if this may contribute to my difficulties seeing things.

Does this look like dirt I could clean off with something like Baader wonderfluid or does it look like scratches? First image shows definate bright halos around my bedroom lights.

[jetstream]

Any scatter hurts when viewing near bright objects, but our eyes also have scatter...for the fun of it take your EP's outside at night and look through both ends of them at a near streetlight... expensive eyepieces will show the effect your going to see. That being said, EP scatter does matter- I personally love orthos for their low scatter or good plossls like TV's.

Just hang on for a bit though and try your objects again and realize that the Flame is very faint- but it is a "bright" faint nebula, many are much fainter than this. Under VG skies it stands right out- I prefer no filter, but a UHC can help a wee bit, but it dims much of it.

M81/M82 can be hard to find, I use some faint stars to locate it but they may not be visible to you at your site. Keep trying!

[pipnina]

Any scatter hurts when viewing near bright objects, but our eyes also have scatter...for the fun of it take your EP's outside at night and look through both ends of them at a near streetlight... expensive eyepieces will show the effect your going to see. That being said, EP scatter does matter- I personally love orthos for their low scatter or good plossls like TV's.

Just hang on for a bit though and try your objects again and realize that the Flame is very faint- but it is a "bright" faint nebula, many are much fainter than this. Under VG skies it stands right out- I prefer no filter, but a UHC can help a wee bit, but it dims much of it.

M81/M82 can be hard to find, I use some faint stars to locate it but they may not be visible to you at your site. Keep trying!

I've just been looking at a way to star hop to M81/82. And I think i've found a method that should work. By going past a "box" of stars and following it in a straight line up to m81/82 in my finder and using some stars of similar brightness to tell me when to stop.

I've been thinking I could try printing out annotated screenshots like this and use these to help me get to objects instead of my star charts... Since the star charts are a bit small on A4.

One thing, though... Is that i looked in stellarium and 30UMA is made of a mag 5.25 and a mag 5.35 star... This conflicts with Stu's info. Perhaps one of these programs (or both) are wrong? Or we were looking at different stars..

If a mag 5.25 and a mag 5.35 star are that close together... Will their brightness add and become like mag 4.8or something?

[Stu]

I reckon this is the best star hop to M81/82. Takes you right to them.

[Stu]

I've just been looking at a way to star hop to M81/82. And I think i've found a method that should work. By going past a "box" of stars and following it in a straight line up to m81/82 in my finder and using some stars of similar brightness to tell me when to stop.

I've been thinking I could try printing out annotated screenshots like this and use these to help me get to objects instead of my star charts... Since the star charts are a bit small on A4.

One thing, though... Is that i looked in stellarium and 30UMA is made of a mag 5.25 and a mag 5.35 star... This conflicts with Stu's info. Perhaps one of these programs (or both) are wrong? Or we were looking at different stars..

If a mag 5.25 and a mag 5.35 star are that close together... Will their brightness add and become like mag 4.8or something?

Acey's info from Simbad agrees with SkySafari that I quoted so it would seem Stellarium is incorrect in this case.

[jetstream]

Acey has provided many of us much info and the link to Simbad, piles of accurate info in there...

[jetstream]

Good star hop Stu, I line up Phecda thru Dubhe, and use the triangle to confirm 24 Ursae and its companion put the Rigel outer circle on it-24- and bam right in the EP All those stars are easily visible from dark, transparent skies.

[acey]

If a mag 5.25 and a mag 5.35 star are that close together... Will their brightness add and become like mag 4.8or something?

Vizier (via the CDS Portal) gives the V-magnitudes of the two components of 30UMa (aka CCDM 09521+5404) as 5.0 and 5.6.

http://vizier.u-strasbg.fr/viz-bin/VizieR-S?CCDM%20J09521%2b5404AB

To the naked eye the pair look like a single star, and we want to know what the combined apparent magnitude will be. We need to turn the (logarithmic) magnitudes m₁,m₂ into (linear) intensities, add the intensities together, then turn the result back into a magnitude m. We can do it in one go using the formula

m = -log(2.512 ^–m₁ + 2.512 ^{– m₂})/log2.512

With the values m₁ = 5.0 and m₂ = 5.6 we get the result m = 4.506. Simbad nevertheless gives the total V-magnitude of 30UMa as 4.560

http://simbad.u-strasbg.fr/simbad/sim-id?Ident=CCDM+J09521%2B5404AB&NbIdent=1&Radius=30&Radius.unit=arcmin&submit=submit+id

So we look at the data sources for the total V-magnitude as measured by various surveys, and we find that the most recent are consistent at 4.60

http://simbad.u-strasbg.fr/simbad/sim-id?mescat.ubv=on&Ident=%40537435&Name=*+phi+UMa&submit=display+selected+measurements#lab_meas

We conclude that there is a slight discrepancy (less than a tenth of a magnitude) between the total V-magnitude 4.51 as calculated from data in the CCDM (Catalog of Components of Double & Multiple stars, Dommanget et al, 2002), and the figure 4.60 measured by the other quoted surveys. This is attributable to measurement error: the CCDM magnitudes are only quoted to one decimal place, so an error of as much as a tenth of a magnitude is to be expected.

Why does the Simbad summary give the total magnitude as 4.560, not 4.60 or 4.51? Maybe it’s a misprint, these things happen. But as long as the data sources are all cited it’s easy to check and verify.

The CDS service (Simbad, Vizier etc|) is used by professionals, Stellarium is beloved by amateurs. Neither is infallible, but I know which one I trust more.

Quote from CDS site:

The CDS hosts the SIMBAD astronomical database, the world reference database for the identification of astronomical objects; VizieR, the catalogue service for the CDS reference collection of astronomical catalogues and tables published in academic journals; and the Aladin interactive software sky atlas for access, visualization and analysis of astronomical images, surveys, catalogues, databases and related data.

 

http://cds.u-strasbg.fr/

[pipnina]

Vizier (via the CDS Portal) gives the V-magnitudes of the two components of 30UMa (aka CCDM 09521+5404) as 5.0 and 5.6.

http://vizier.u-strasbg.fr/viz-bin/VizieR-S?CCDM%20J09521%2b5404AB

To the naked eye the pair look like a single star, and we want to know what the combined apparent magnitude will be. We need to turn the (logarithmic) magnitudes m₁,m₂ into (linear) intensities, add the intensities together, then turn the result back into a magnitude m. We can do it in one go using the formula

m = -log(2.512 ^–m₁ + 2.512 ^{– m₂})/log2.512

With the values m₁ = 5.0 and m₂ = 5.6 we get the result m = 4.506. Simbad nevertheless gives the total V-magnitude of 30UMa as 4.560

http://simbad.u-strasbg.fr/simbad/sim-id?Ident=CCDM+J09521%2B5404AB&NbIdent=1&Radius=30&Radius.unit=arcmin&submit=submit+id

So we look at the data sources for the total V-magnitude as measured by various surveys, and we find that the most recent are consistent at 4.60

http://simbad.u-strasbg.fr/simbad/sim-id?mescat.ubv=on&Ident=%40537435&Name=*+phi+UMa&submit=display+selected+measurements#lab_meas

We conclude that there is a slight discrepancy (less than a tenth of a magnitude) between the total V-magnitude 4.51 as calculated from data in the CCDM (Catalog of Components of Double & Multiple stars, Dommanget et al, 2002), and the figure 4.60 measured by the other quoted surveys. This is attributable to measurement error: the CCDM magnitudes are only quoted to one decimal place, so an error of as much as a tenth of a magnitude is to be expected.

Why does the Simbad summary give the total magnitude as 4.560, not 4.60 or 4.51? Maybe it’s a misprint, these things happen. But as long as the data sources are all cited it’s easy to check and verify.

Simbad is used by professionals, Stellarium is beloved by amateurs. Neither is infallible, but I know which one I trust more.

So to the naked eye, 30UMA is a 4.5-4.6 mag star? Cheers for clarifying!

So I'm checking some stars out on Simbad, but the pages for them only state spectral type, parallax & coordinates... No mention of brightness, do I have to do something to get this info?#

Cheers for the help,

    ~pip

[pipnina]

Something else: When Trying to determine my NELM, should I be thinking about "Extincted" magnitude or the non-extincted magnitude? Or should I just look for stars at or near the zenith?

[jetstream]

You can profile your sky by tracking the faintest ones visible from horizon to zenith, which will indicate the amount of stuff in your atmosphere. For NELM, when seriously trying to check (not often) I use the zenith. The very best skies show the least difference from horizon to zenith assuming it's very dark to start with.

Obviously "seeing"  can be good when there is light cloud or haze in the atmosphere.

Using an SQM-L will show you high potential dark sites, from there you can pick the ones with the best transparency, IMHO.