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What are "bright" DSOs, really?


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In many threads for beginners, the more experienced people keep saying that "this or that scope will allow you to see the moon, the planets, and the bright DSOs". But what enters the category of the bright DSOs? For typical city conditions (say Bortle 7, which seems to be a good average of people writing on here) is this just a few open clusters and maybe one or two globular clusters and Andromeda with averted vision?

I realize that this will depend on many factors, but since I keep reading this generic comment, I would like to get a generic answer to my question, I'm not looking for a list of all the objects I can hope to see ;)

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Basically yes, add in Orion nebula also. Generally probably magnitude 5/6 or higher. Clusters tend to be a bit easier as they're clustered groups of stars but you'd be surprised how dim they actually are from light polluted skies, starfields/open clusters usually no issue. I'm bortle 7 and have to use averted vision as clusters are so dim even through a 6 inch scope.

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34 minutes ago, SwiMatt said:

this will depend on many factors

I would say Messier objects that appeared in the first catalogue ( M1 to M45) would be a good starting point. Even so, most first time observers react with a "err is that it? That faint grey bit I can see?"

Saturn however never fails to impress the first time!

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Magnitude is actually a bad measure for brightness of a DSO. Surface brightness is much more important. M101 is magnitude 7.9, but is far harder to spot than M82, at magnitude 8.4 or M57 at magnitude 8.8.  Many planetary nebulae are very easy, even from light-polluted areas, partly because of a high surface brightness, but even more because narrow-band filters allow picking them out easily, while effectively reducing light pollution. Most globular clusters have good surface brightness, as do quite a few elliptical galaxies. Narrow-band filters do not work under these circumstances.

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The British Astronomical Association includes double / multiple stars in the DSO heading however some other sources don't include them as such.

Nevertheless they are often good targets under light polluted skies 🙂

 

 

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15 minutes ago, John said:

The British Astronomical Association includes double / multiple stars in the DSO heading however some other sources don't include them as such.

Nevertheless they are often good targets under light polluted skies 🙂

 

 

Not only under light polluted skies, and they are great targets even with smaller instruments! :D

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A  few that come to mind are m31, m81, m82,  m42, m45, m13, m15, m3, Eskimo nebula, m39, double cluster, m35, 36, 37, 38.  A few clusters in cassiopeia (m103 if I remember correctly).  These are a few off the top of my head that I could see with a 6" newt from a Bortle 7 sky.

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2 minutes ago, bish said:

A  few that come to mind are m31, m81, m82,  m42, m45, m13, m15, m3, Eskimo nebula, m39, double cluster, m35, 36, 37, 38.  A few clusters in cassiopeia (m103 if I remember correctly).  These are a few off the top of my head that I could see with a 6" newt from a Bortle 7 sky.

So many more than one would expect! I imagine that those are not regular sightings, right? They will depend on conditions and position in the sky (and with averted vision?)

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57 minutes ago, SwiMatt said:

So many more than one would expect! I imagine that those are not regular sightings, right? They will depend on conditions and position in the sky (and with averted vision?)

Yes - it is very important for conditions to be right. Good transparency and good position in the sky - which is usually overhead near the zenith - unless there is particular patch of the sky that is darker (like when you are on the edge of the city and there is one direction with lower LP).

I just dug up one of my old reports. Bortle 7 / red zone, 4" fast achomatic refractor:

M8, M20, M17, M16, M18, M24,  M2, M28, M22, NGC6638 and NGC6642 (Very faint, peripheral vision), M25, M26 and M11

This was summertime, I was on the edge of white / red zone and observing in the direction of the least LP (due south - which helped).

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There are also a number of small planetary nebulae that are very bright, such as the Catseye Nebula, the Blinking Planetary and the Eskimo Neb as already mentioned. Easy to see, but not always so easy to find! 

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Thank you all for these reports and short lists. It seems like even with a "smaller" scope there can be so much to see from a light polluted area. I'm glad I asked :D

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If you have a big scope (8" minimum), and if you can get it on target, big/nearby globular clusters will resolve at high powers (>200x) even under moderately light polluted skies (Bortle 5 to 7).  They aren't as spectacular as under dark skies, but they are certainly visible as more than just a smudge.  In smaller scopes, they generally just remain smudges due to resolving power issues.

Compact open clusters also resolve nicely at higher powers in smaller scopes under moderately light polluted skies as has been mentioned above.  Smaller, more distant OCs will require more aperture and higher powers to resolve as with GCs.

Even brighter nebula benefit from using line filters in light polluted skies.  The Veil Nebula goes from invisible to wow with a premium OIII filter in my 15" Dob under Bortle 5 conditions.

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Lots of good comments already and I would only add that if you can find a dark spot and can stay out of direct light sources you will be amazed by the difference that dark adaptation can make. I live under Bortle 5/6 skies but there are a few dark corners in my garden where I can avoid street lights neighbours lights etc. It makes a great difference to not only my naked eye views of the sky helping to star hop more easily but also my telescopic views.

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"Bright DSO" is only relative to the skies you observe from and the aperture you use IMHO. No matter how well my TSA120 does under very dark skies it cannot touch my 10" dob for DSO. Regardless of some opinions, a 10" dob, under LP skies will outperform a 100mm-140mm class scope every time.

Take a small scope, put it under dark skies and it will amaze wih the views it gives... our H130 gives a stupidly bright view of M81/M82...and M42...and...👍

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5 hours ago, SwiMatt said:

So many more than one would expect! I imagine that those are not regular sightings, right? They will depend on conditions and position in the sky (and with averted vision?)

A nice clear sky and the higher the better.  Some, such as m39 (a fairly bright open cluster) can be seen under poorer conditions than any of the galaxies. M51 and m64  are other galaxy that should be visible but need to be high in a clear moonless sky.  Ideally  a new moon or within first few days of new moon, especially for galaxies. Under good conditions none should need averted vision. Under a really datk sky there is a huge amount to be seen even with a good pair of bins.

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4 hours ago, SwiMatt said:

Thank you all for these reports and short lists. It seems like even with a "smaller" scope there can be so much to see from a light polluted area. I'm glad I asked :D

Just remember that observing is a skill that you improve with practice. We actually learn how to see those faint objects and it is important to spend time under stars.

On numerous occasions I've read and later witnessed that myself - in the beginning what we call bright DSOs - don't seem bright at all - but there comes a time, after observing faint and very faint stuff that one gets surprised by how bright those targets really are in comparison.

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2 hours ago, vlaiv said:

Just remember that observing is a skill that you improve with practice. We actually learn how to see those faint objects and it is important to spend time under stars.

On numerous occasions I've read and later witnessed that myself - in the beginning what we call bright DSOs - don't seem bright at all - but there comes a time, after observing faint and very faint stuff that one gets surprised by how bright those targets really are in comparison.

Thanks for the encouraging suggestion! My first nights under the stars were amazing but also slightly overwhelming due to seeing only few exetremely bright things. I can't wait to spend more time under the stars though!

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Agree with Gerry (jetstream) above.

"Bright DSOs" is used for "the brightest DSOs given aperture and sky darkness".

The vast majority of targets in this hobby require a certain amount of "study" and "re-visits" to be appreciated. It takes dedication and patience, a bit like fishing.. 🙂

"Bright targets" is also used for objects that can be spotted relatively easily, but they cannot really be observed. For instance, I spotted a few planetary nebulae with my TV60 under moderately polluted bright skies with or without filters. However, excluding a very limited number of bright and large PNs (e.g. M27, M57) this remains a tick exercise (and a few members have this kind of approach with this hobby) using small apertures. I really started appreciating them using at least moderate powers (at least 250-300x and much more) with my 16". That is when some structure starts showing up and therefore the target can be studied.

Edited by Piero
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4 hours ago, Piero said:

Agree with Gerry (jetstream) above.

"Bright DSOs" is used for "the brightest DSOs given aperture and sky darkness".

The vast majority of targets in this hobby require a certain amount of "study" and "re-visits" to be appreciated. It takes dedication and patience, a bit like fishing.. 🙂

"Bright targets" is also used for objects that can be spotted relatively easily, but they cannot really be observed. For instance, I spotted a few planetary nebulae with my TV60 under moderately polluted bright skies with or without filters. However, excluding a very limited number of bright and large PNs (e.g. M27, M57) this remains a tick exercise (and a few members have this kind of approach with this hobby) using small apertures. I really started appreciating them using at least moderate powers (at least 250-300x and much more) with my 16". That is when some structure starts showing up and therefore the target can be studied.

I understand the difference between "spotting" and "observing" as you describe it here, and I can totally see that like you I want to observe and not just spot. But I would disagree that spotting at this level remains a tick exercise. As a newcomer, it's extremely exciting to spot things I had no idea I could even just spot. For sure observing them will give me another type of pleasure, but spotting is not devoid of appreciation, I think :) not really taking away from your point, though!

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Q. "What are "bright" DSOs, really?"

A. They are easily visible small grey smudges, as compared to barely visible, wispy grey smudges.

🙂

Dave

Edited by F15Rules
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56 minutes ago, F15Rules said:

Q. "What are "bright" DSOs, really?"

A. They are easily visible small grey smudges, as compared to barely visible, wispy grey smudges.

🙂

Dave

From my back garden using a 4” frac ‘Smudges’ or ‘Fuzzies’ are great descriptions of DSO’s.

Two that have frustrated & eluded me the most are face on galaxies M33 in Triangulum & M101 in Ursa Major! 
 

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