106 replies to this topic

[bazookaman]

So far I think I'm pretty limited to mag 9 galaxies with my 10" dob at bortle 5 (19.6 measured, no moon) site. The 9's I've found are just on the edge of visibility, some averted vision. However, it seems that a huge # of galaxies start at 10 mag and I'm wondering how I can get there? Which is more important, more aperture or darker skies?

 

I ask because I'm searching for dark site property to buy for observation, along with general recreational use (kids playing, camping, treehouse, etc). Of course, the further I'm willing to drive, the darker it gets. At 2 hours, I can get to 21.8+ and have found some options. But at this distance, the sessions would be limited to overnight camping and wouldn't be a single night out-and-back which would cut down on usage. Right now my 19.6 site is about 30 minutes and I consider it a very easy drive. I am only limited to the park closing at 10p so I have to wrap up my session no later than 9:45p.

 

Anyway, I was curious, if I get into 21.5+ skies, is my 10" going to be enough to get those numerous 10+ mag galaxies and all of those nebula? Or would I need a larger scope as well? I've not observed from darker than 19.6 yet. I've been to darker sites, but the moon was close to full.

[Augustus]

I've done 11th mag with a 10" under SQM 19.6, and 12th mag galaxies with a C9.25 under SQM 20.6. My 16" and 20.5" were hitting 14th mag from my SQM 19.6 backyard.

 

Flock your scope, learn what magnifications are optimal and preserve your dark adaptation and you can at least hit 10th mag.

[Astrojensen]

Dark skies are OVERWHELMINGLY more important for galaxies than aperture. Under my SQM 21.7 rural skies, I can EASILY see mag. 10 galaxies in my 63mm achromat and my 12" goes beyond mag 14. 

 

 

Clear skies!

Thomas, Denmark

[Inkswitch]

Which is more important, more aperture or darker skies?

 

I am only limited to the park closing at 10p so I have to wrap up my session no later than 9:45p.

 

While aperture helps, dark skies help more.  The darker the better, this cannot be overstated.

 

I often find better conditions after midnight.  The objects on the ground around you have lost the heat they gained by sitting in the sun all day.  Another helpful action on your part would be to observe in the wee hours though life often intervenes.

Edited by Inkswitch, 10 January 2021 - 12:47 PM.

[eyeoftexas]

See EAA or Night Vision Forums for alternative approaches.  I've used EAA to see almost all of the Herschel 400 objects, including those tiny dim galaxies (Mag 11-12) under Bortle 7/8 skies.

[havasman]

Dark skies are much more valuable than aperture. Aperture gets wasted under light pollution. If you ever take advantage of the 21.8 sky you have available the drive will seem much more worthwhile. Your XT10 and fine eyepiece kit will certainly show thousands more galaxies and other objects from under dark skies. The objects you now observe will be more extended with much more available detail. It's an entire new level of capability that dark sky brings. I never even bother to use the Starmaster from town as it isn't productive. If I had to choose between my XT10i from a dark site and the 16" from town I would choose the 10" from a dark site. 

And judging under a large moon isn't effective.

You have some real treats waiting for you!

[Keith Rivich]

So far I think I'm pretty limited to mag 9 galaxies with my 10" dob at bortle 5 (19.6 measured, no moon) site. The 9's I've found are just on the edge of visibility, some averted vision. However, it seems that a huge # of galaxies start at 10 mag and I'm wondering how I can get there? Which is more important, more aperture or darker skies?

<...snip...>

Have you been out to the HAS site in Columbus? Plenty dark enough for serious observing and only 1 1/2 hour drive from downtown Houston. 

 

Would be a good place to see just how deep you can go and still be close to home!

[Love Cowboy]

As VP of HAS, I wholeheartedly concur with Keith's recommendation. Your scope will easily pull in 10-12th mag galaxies from our dark site and you get 24/7 access to that site included in your membership with no extra charge.



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[Allan Wade]

Something I’ve observed. As you move to progressively darker skies, there are two classes of objects that improve more significantly than the others, and they are galaxies and dark nebula. As you progressively increase aperture, there are two classes of objects that improve more significantly than the others, and they are galaxies and planetary nebula.

 

I enjoy observing galaxies above all else, and I agree with the other posters that I would be seeking out the darker skies first. Plus you can’t beat the thrill of observing under a dark sky, it just looks magnificent. A 10” dob is a great place to develop your skills as well. If you jump to a bigger scope too quick, it can make you lazy as the larger aperture just hands you up all this faint stuff on plate. You won’t have the skill to use the bigger scope to eventually see the really faint stuff.

 

At my city Bortle 5 home I never look at galaxies, I save them for my dark site trips. At my dark site I can see the magnitude 10 Messiers in my 10x50 binoculars, so your 10” will rock those targets. You’ll be into the magnitude 12 galaxies, and aiming for the magnitude 13’s as you gain experience. With each one magnitude deeper you go, the number of visible galaxies rises exponentially, so you’ll soon have more things to look at than you will ever get through in a 10”.

[Redbetter]

At a dark site a 10" readily shows 14 to 15 mag galaxies.  

 

Galaxies and diffuse nebula observing is primarily about contrast between the night sky and fixed surface brightness of the object.  More aperture doesn't change this surface brightness delta.  If the contrast is too poor to show the galaxy, you won't see it, even though in dark skies the galaxy would be easily seen.

 

M110 is a good example for this.  Despite being about 8.1 visual magnitude, it is diffuse with only moderately higher surface brightness to its core.  It is easy and obvious in dark sky with nearly any aperture, but hard to detect in light polluted conditions.  In ~19 MPSAS conditions in town it is just visible as a faint averted vision haze if transparency is very good--primarily because it has some brightening to the center that is detectable.  I calculate its overall visual surface brightness as ~22.7 MPSAS.  A 22.7 - 19 = 3.7 MPSAS delta is difficult to pick up, even for someone who knows exactly where to look and what they are looking for.  Aperture is not the problem.

[Starman1]

So far I think I'm pretty limited to mag 9 galaxies with my 10" dob at bortle 5 (19.6 measured, no moon) site. The 9's I've found are just on the edge of visibility, some averted vision. However, it seems that a huge # of galaxies start at 10 mag and I'm wondering how I can get there? Which is more important, more aperture or darker skies?

 

I ask because I'm searching for dark site property to buy for observation, along with general recreational use (kids playing, camping, treehouse, etc). Of course, the further I'm willing to drive, the darker it gets. At 2 hours, I can get to 21.8+ and have found some options. But at this distance, the sessions would be limited to overnight camping and wouldn't be a single night out-and-back which would cut down on usage. Right now my 19.6 site is about 30 minutes and I consider it a very easy drive. I am only limited to the park closing at 10p so I have to wrap up my session no later than 9:45p.

 

Anyway, I was curious, if I get into 21.5+ skies, is my 10" going to be enough to get those numerous 10+ mag galaxies and all of those nebula? Or would I need a larger scope as well? I've not observed from darker than 19.6 yet. I've been to darker sites, but the moon was close to full.

Dark skies.  As Redbetter says, a 10" in truly dark skies will not have an issue with seeing galaxies until they pass mag.14.

Then it will be a matter of transparency and experience to see fainter.

[maroubra_boy]

I suspect there may be other reasons why you may be struggling to see more galaxies from your Bortle 5 skies.  You should be seeing many dozens of galaxies with your 10" scope.

 

From the info i can see, you are new to astro, so I suspect the main reason for you not seeing more galaxies is actually inexperience. 

 

I live under a Bortle 8 sky & can see many dozens of galaxies using my 9 Mak, down to magnitude 10.5 on a night of average transparency.  But I have also been using scopes for 38 years.  Inexperience means your skills need developing, and expecations also tempered/moulded.  A 10" scope is capable of starting to show the spiral structure in the larger, brighter galaxies, but not under a Bortle 5 sky.  You will be able to just see the core of galaxies at best.  If your expectation is to see resplendent spiral structures like a Hubble photo, you are in for a major disappointment, even with a larger scope. 

 

Transparency of your local sky is another MAJOR factor impacting the ability to see DSO's, AND detail in them.  If where you live is prone to haze, fog, mist, etc, this will greatly impact on what light does get through to your scope and eyes.  And this could also be a seasonal thing, say with winter offering a clearer sky than summer.

 

How to get the most out of a scope is more involved than just aperture and how dark a sky is. 

 

Alex.

Edited by maroubra_boy, 10 January 2021 - 06:27 PM.

[maroubra_boy]

Site selection is also more involved than just a dark location or some SQM reading or evdn a 2 hour drive.  Not give a site the necessary attention & study that is needed and you may end up just getting a dew trap that may have a wonderful SQM reading, but crap transparency more often than not.

 

An SQM will only give a blind objective value of how dark a sky is.  It WILL be affected by a bright Milky Way as well as a sky subdued by haze/mist that will darken the sky, and is totally incapable of differentiating/distinguishing/evaluating such conditions.  If you do not know how to properly research the astro viability of a site, these values are essentially meaningless.  An SQM reading means nothing without the context of transparency and aspect of the Milky Way. 

 

If you are wanting to get more out of your scope and astro experience, excellent!  Slow down and be patient with your scope, and yourself.  Learning to use a scope takes time as it means teaching your eyes how to see in low light conditions and also how to recognize atmospheric conditions that are not just optimal for astro but also this means learning how to adapt your viewing to best suit conditions on any given night.  No use chasing galaxies if transparency isn't much chop... change to chasing open clusters or planets or asteroids instead.  The Moon also has so much to offer, including the Full Moon!  It is NOT the nemisis of astronomers that it is made out to be.  Ignorance of what can be seen on the Moon is its greatest problem.  If the Moon is up, adapt your plans for it or with it.

 

Like I said in my previous post, if you are not seeing more than a handful of galaxies under a Bortle 5 sky then there are other underlying factors at play.  Could be inexperience, location/microclimate, expectations, even eyesight.  Even how you are using your scope.  A 10" scope under Bortle 5 skies should be revealing dozens of galaxies to you.  And if not then just saying "sure, go drop a stack of cash on a dark site property" is only doing you a disservice, not helping you.  If NOW you don't understand why you are not seeing what you expect, you sure are not going to be making a property decision that WILL actually give you what you want for your astro experience.  And this also goes for a larger scope.

 

Alex.

Edited by maroubra_boy, 10 January 2021 - 08:16 PM.

[bazookaman]

Thanks for the info everyone.

 

 

See EAA or Night Vision Forums for alternative approaches.  I've used EAA to see almost all of the Herschel 400 objects, including those tiny dim galaxies (Mag 11-12) under Bortle 7/8 skies.

I think EAA is something I could see myself getting into for sure, but I right now I really like the raw seeing aspect of the hobby. It's like my mind is directly connected to what I'm looking at, instead of seeing an interpretation.

 

 

Dark skies are much more valuable than aperture. Aperture gets wasted under light pollution. If you ever take advantage of the 21.8 sky you have available the drive will seem much more worthwhile. Your XT10 and fine eyepiece kit will certainly show thousands more galaxies and other objects from under dark skies. The objects you now observe will be more extended with much more available detail. It's an entire new level of capability that dark sky brings. I never even bother to use the Starmaster from town as it isn't productive. If I had to choose between my XT10i from a dark site and the 16" from town I would choose the 10" from a dark site. 

And judging under a large moon isn't effective.

You have some real treats waiting for you!

You're getting me all excited!

 

 

Have you been out to the HAS site in Columbus? Plenty dark enough for serious observing and only 1 1/2 hour drive from downtown Houston. 

 

Would be a good place to see just how deep you can go and still be close to home!

I have not but I've read about it on the site. I think that's actually a really good idea as it would provide me a realistic test of both a darker site and a longer drive, including overnight stay in a tent. Maybe that would satiate me for a while and give me more time to find a property that would better fit our other needs. I think I'll sign up. Thanks for the reminder.

 

 

Something I’ve observed....

I think my favorite way to observe right now is just putting on a low mag and panning around. Not being very familiar with where things are, it's exciting to "discover" something new. Just the other night I was in my driveway cruising southeast of Orion and ran across a few OC's that I hadn't see yet. I would like to be able to do this very same thing with galaxies... just happen across them, and then ID them.

 

 

At a dark site a 10" readily shows 14 to 15 mag galaxies.  

 

Galaxies and diffuse nebula observing is primarily about contrast between the night sky and fixed surface brightness of the object.  More aperture doesn't change this surface brightness delta.  If the contrast is too poor to show the galaxy, you won't see it, even though in dark skies the galaxy would be easily seen.

 

M110 is a good example for this.  Despite being about 8.1 visual magnitude, it is diffuse with only moderately higher surface brightness to its core.  It is easy and obvious in dark sky with nearly any aperture, but hard to detect in light polluted conditions.  In ~19 MPSAS conditions in town it is just visible as a faint averted vision haze if transparency is very good--primarily because it has some brightening to the center that is detectable.  I calculate its overall visual surface brightness as ~22.7 MPSAS.  A 22.7 - 19 = 3.7 MPSAS delta is difficult to pick up, even for someone who knows exactly where to look and what they are looking for.  Aperture is not the problem.

 

I'm able to see M110 at the 19.6 site fairly easily. No structure, but I haven't really seen any structure to any galaxy yet... not obvious anyway.

 

Dark skies.  As Redbetter says, a 10" in truly dark skies will not have an issue with seeing galaxies until they pass mag.14.

Then it will be a matter of transparency and experience to see fainter.

Can't wait!

 

 

I suspect there may be other reasons why you may be struggling to see more galaxies from your Bortle 5 skies....

I'm sure inexperience has plenty to do with it, but also probably my observing method. I generally just use Sky Safari (pro) and look zoom in and start searching for the first thing I see. Not very methodical for sure. And I also am aware that magnitude isn't really the best way to determine if a galaxy is bright enough to see, but I can't figure out a way to filter surface brightness on any of my apps. They seem to love magnitude and SB seems to be an afterthought. But it could be my inexperience with using those apps too.

 

For some reference, at Brazos Bend SP, which I recently measured at 19.65 upon arrival around 7p and 19.68 upon departure at 9:30p, some objects that were at what I would consider the edge of my ability to locate/see are:

 

M74 (logbook says "faintest of smudges", and "extremely faint galaxy, averted vision only" on two separate nights)

NGC 288 (GC) ("edge of visibility with direct vision, @30mm just a cloud, at 11mm start see individual grains of stars")

NGC 253 ("very faint smudge w/ 20mm")

Attempted NGC 247, couldn't locate

M33 ("very faint galaxy in Triangulum")

 

Does this seem to be about right? Does anyone have any suggestions for dim targets at the edge of my conditions that I should be able to find? I wouldn't mind an assignment for my next time out. That's would give me some direction at least and I can report back how I ended up...

 

Thanks again for the feedback everyone. Much appreciated.

[Starman1]

First, don't use Sky Safari if looking for faint objects, or wait 15 minutes between looking at the screen and looking through the eyepiece.

You can't maintain good night vision for faint objects and use a tablet.

Second, before looking for something faint, wait 30-45 minutes outside away from lights.

Third, use averted vision to look for the object and to study it.  Your direct vision isn't as sensitive to light.

[Redbetter]

I am surprised that Brazos Bend is that bright now.  It was much darker than that back in the early 2000's when I observed from there.  The numbers you gave are suburban bright.  Houston's light pollution is pretty bad, but that is getting ridiculous.  Of course, 9:30 pm is not what I would expect to be near the dark portion of the night either.  My saying is, "the real observing begins after midnight."

[Love Cowboy]

I am surprised that Brazos Bend is that bright now.  It was much darker than that back in the early 2000's when I observed from there.  The numbers you gave are suburban bright.  Houston's light pollution is pretty bad, but that is getting ridiculous.  Of course, 9:30 pm is not what I would expect to be near the dark portion of the night either.  My saying is, "the real observing begins after midnight."

I've never bothered with Brazos Bend as I have the much darker HAS dark site at my disposal, but yes, Houston's light pollution has gotten much worse in recent years.  

[Voyager 3]

First, don't use Sky Safari if looking for faint objects, or wait 15 minutes between looking at the screen and looking through the eyepiece.
You can't maintain good night vision for faint objects and use a tablet.
Second, before looking for something faint, wait 30-45 minutes outside away from lights.
Third, use averted vision to look for the object and to study it. Your direct vision isn't as sensitive to light.

Are there any star atlases or finder charts with stars upto 13-14 mag ? Would be really helpful.

[Starman1]

Are there any star atlases or finder charts with stars up to 13-14 mag ? Would be really helpful.

Not printed ones.

But if you download the free star atlas Cartes du Ciel (it's in English), you can make a chart at any scale with stars a lot fainter than that,

and print at your discretion.  You can also have as many or as few deep sky objects as desired.

You might download some of the free observing books here.  They have excellent finder charts for each object:

http://faintfuzzies....ingGuides2.html

Thee are some beginner's stuff there too.

 

And if you download the "C" atlas here:

https://allans-stuff.com/triatlas/

the stars will go as faint as you want.  Caution: its a LOT of ages if you print the whole thing.

Edited by Starman1, 11 January 2021 - 02:10 AM.

[bazookaman]

First, don't use Sky Safari if looking for faint objects, or wait 15 minutes between looking at the screen and looking through the eyepiece.

You can't maintain good night vision for faint objects and use a tablet.

Second, before looking for something faint, wait 30-45 minutes outside away from lights.

Third, use averted vision to look for the object and to study it.  Your direct vision isn't as sensitive to light.

 

Right on. So even the red light from sky safari messes up night vision? I don't understand how that'd be different than looking at map with a (probably brighter) red light.

 

 

I am surprised that Brazos Bend is that bright now.  It was much darker than that back in the early 2000's when I observed from there.  The numbers you gave are suburban bright.  Houston's light pollution is pretty bad, but that is getting ridiculous.  Of course, 9:30 pm is not what I would expect to be near the dark portion of the night either.  My saying is, "the real observing begins after midnight."

 

Pearland has blown up since we moved there in 2006, and now I live south closer to 6 which is developing too. The light dome looking north is terrible. South is better, but my measurement was at zenith.

 

 

I've never bothered with Brazos Bend as I have the much darker HAS dark site at my disposal, but yes, Houston's light pollution has gotten much worse in recent years.  

How does the HAS site measure?

 

Also, how are the light pollution maps calculated? Lightpollutionmap.info has Brazos as a 20.58 (at the point where I observe from). My measurement is way off that mark, so I wonder how these maps are generated and how often they are updated.

 

Not printed ones.

But if you download the free star atlas Cartes du Ciel (it's in English), you can make a chart at any scale with stars a lot fainter than that,

and print at your discretion.  You can also have as many or as few deep sky objects as desired.

You might download some of the free observing books here.  They have excellent finder charts for each object:

http://faintfuzzies....ingGuides2.html

Thee are some beginner's stuff there too.

 

And if you download the "C" atlas here:

https://allans-stuff.com/triatlas/

the stars will go as faint as you want.  Caution: its a LOT of ages if you print the whole thing.

I'll give those a browse and a bookmark.

[Love Cowboy]

I've never measured the HAS site that way, but it's much better than Brazos Bend, I guarantee it.

The light pollution maps are likely out of date for the Houston area. It's spiked significantly in the last few years due to the unfortunate replacement of the streetlights with WHITE LEDS.

As far as your question about red light messing up night vision, yes, ALL light messes up your night vision, even red light on your chart. The difference is simply how much. Additionally, device screen light is still emitting full-spectrum even if it is on "night mode". Unless you've got a physical red filter over your screen, you're still getting other light.

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[bazookaman]

Not printed ones.

But if you download the free star atlas Cartes du Ciel (it's in English), you can make a chart at any scale with stars a lot fainter than that,

and print at your discretion.  You can also have as many or as few deep sky objects as desired.

You might download some of the free observing books here.  They have excellent finder charts for each object:

http://faintfuzzies....ingGuides2.html

Thee are some beginner's stuff there too.

 

And if you download the "C" atlas here:

https://allans-stuff.com/triatlas/

the stars will go as faint as you want.  Caution: its a LOT of ages if you print the whole thing.

Looking at Cartes de Ciel now, is there a way to filter by surface brightness? Isn't that a better metric than mag?

[Starman1]

When looking for faint objects at the limit, dark adaptation is essential.

There are levels of dark adaptation:

--the level where you can walk around at night and use a bright red flashlight.  This is the level you can maintain with a red screened tablet.

--the level where you can see details in your surroundings and a red LED flashlight has to be turned almost off before it is not too bright.  This is the level needed to read a chart with indirect light.

--the level where any light of any kind is too bright and you can see to walk around without a light.

--the level where you can walk into the woods and see to walk without a light and the clearing behind you seems moonlit, even though there is no moon in the sky

--the level where the light of the sky itself damages your night vision and causes you to squint and you can see a black eyepiece cap dropped on a black cloth on the ground

and see the millimeter markings on your eyepieces without a light.

 

The depth to which you can see in the telescope varies by well over a magnitude between the first level and the last and possibly more.  Very few people get to that last level, ever.

It is achievable by staring at the ground until you can see wrinkles in a black cloth (probably 5 minutes or more), then looking through the eyepiece while blocking all peripheral light

with a hood or black cloth over the head.

[bazookaman]

I've never measured the HAS site that way, but it's much better than Brazos Bend, I guarantee it.

The light pollution maps are likely out of date for the Houston area. It's spiked significantly in the last few years due to the unfortunate replacement of the streetlights with WHITE LEDS.

As far as your question about red light messing up night vision, yes, ALL light messes up your night vision, even red light on your chart. The difference is simply how much. Additionally, device screen light is still emitting full-spectrum even if it is on "night mode". Unless you've got a physical red filter over your screen, you're still getting other light.

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Good to know, I wasn't aware of that.

[Starman1]

Looking at Cartes de Ciel now, is there a way to filter by surface brightness? Isn't that a better metric than mag?

Perhaps, but magnitude is the normal sort.

Most faint objects are small and the spread between total integrated magnitude and surface brightness is smaller.

M33 has a total integrated magnitude of 5.7, but a surface brightness average of 14.1

That's because it is large.  A face-on galaxy of magnitude 10 that is 1' wide also has a surface brightness of magnitude 10.