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Observing >> Deep Sky Observing

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saemark30
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Reged: 02/21/12

How Many Messier Objects Are Visible in The City ? new
      #6148842 - 10/20/13 06:22 PM

Assuming I use 25x100 binocs, how many of these objects are visible in mag 4.5 skies?
This is 18.5 mag/sq arc secs skies using a skymeter.
I assume the fainter galaxies are the hardest hit by light pollution.


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Tony Flanders
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Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: How Many Messier Objects Are Visible in The City ? new [Re: saemark30]
      #6149350 - 10/21/13 07:22 AM

Quote:

Assuming I use 25x100 binocs, how many of these objects are visible in mag 4.5 skies?
This is 18.5 mag/sq arc secs skies using a skymeter.
I assume the fainter galaxies are the hardest hit by light pollution.




For what it's worth, I can see stars considerably fainter than 4.5 when my SQM reads 18.5.

In any case, I'd say you have a good shot at seeing all the Messier objects with that instrument under those skies. The toughest ones will be galaxies with low surface brightness (M98, M101, M74, M33), small objects where low 25X magnification is a serious handicap (M76), and objects that are low in the skyglow near the horizon.

See my Urban/Suburban Messier Guide. Note that two eyes are really quite a lot better than one -- but not as much as higher magnifications are better than low magnifications. In other words, you should do much better than a 100-mm refractor at 25X, but not as well as a 100-mm refractor at 75X.


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Dave MitskyModerator
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Reged: 04/08/02

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Re: How Many Messier Objects Are Visible in The City ? new [Re: Tony Flanders]
      #6149875 - 10/21/13 01:14 PM

IMO, the four galaxies (and M74 in particular) that Tony mentioned will be extremely difficult, if not impossible, to see.

Dave Mitsky


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CelestronDaddy
scholastic sledgehammer
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Reged: 08/22/09

Loc: Central Texas
Re: How Many Messier Objects Are Visible in The City ? new [Re: Tony Flanders]
      #6150402 - 10/21/13 06:48 PM

Tony, Thanks for your messier link!

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saemark30
Pooh-Bah


Reged: 02/21/12

Re: How Many Messier Objects Are Visible in The City ? new [Re: CelestronDaddy]
      #6155645 - 10/24/13 02:08 PM

I don't have a SQM meter so the figure is just what someone quoted me for my observing site. Limiting mag has been getting worse so it might have been more like 5 or 5.5 in the past, the Milky Way used to be faintly visible overhead but no more.

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starbux
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Reged: 02/08/06

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Re: How Many Messier Objects Are Visible in The City ? new [Re: saemark30]
      #6165193 - 10/29/13 07:17 PM

Rod Mollise's "Urban Astronomer's Guide" is a great resource for hunting urban DSOs, Messiers and others.

http://www.amazon.com/The-Urban-Astronomers-Guide-Practical/dp/1846282160/ref...


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Dave MitskyModerator
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Re: How Many Messier Objects Are Visible in The City ? new [Re: saemark30]
      #6165657 - 10/30/13 02:18 AM

Tips on city observing are posted at the following URLs:

http://www.astroleague.org/al/obsclubs/urban/urbantip.html

http://www.skyandtelescope.com/howto/basics/3303991.html

http://www.astronomy.com/magazine/2007/08/how-to-enjoy-urban-skies

http://www.astronomy.com/News-Observing/Urban%20Skies/2006/12/Setup%20is%20ke...

Urban astronomy is also discussed at these sites:

http://www.dirtyskies.com/

http://washedoutastronomy.com/

http://urbanastronomer.blogspot.com/

Books on the subject include Urban Astronomy by Denis Berthier and The Urban Astronomer's Guide: A Walking Tour of the Cosmos for City Sky Watchers (Patrick Moore's Practical Astronomy Series) by Rod Mollise.

http://www.amazon.com/Urban-Astronomy-Denis-Berthier/dp/052153190X

http://www.amazon.com/Urban-Astronomers-Guide-Practical-Astronomy/dp/1846282160

Lists of deep-sky objects that are visible from urban areas can be found at the following URLs:

http://mysite.verizon.net/vze55p46/id10.html

http://www.astroleague.org/al/obsclubs/urban/urbanld.html

http://www.skyandtelescope.com/observing/objects/projects/3074841.html

http://www.astronomy.com/en/News-Observing/Urban%20Skies/2006/12/Explore%20de...

Dave Mitsky


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RussL
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Re: How Many Messier Objects Are Visible in The City ? new [Re: Dave Mitsky]
      #6168445 - 10/31/13 12:57 PM

I have seen the Sombrero from my red zone in an ST80 at, say, around 50x if that gives any encouragement. But, then again, sometimes not. Even M4 comes and goes at 10x in my binos, as well as many other objects.

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saemark30
Pooh-Bah


Reged: 02/21/12

Re: How Many Messier Objects Are Visible in The City ? new [Re: Tony Flanders]
      #6168468 - 10/31/13 01:06 PM

Quote:


For what it's worth, I can see stars considerably fainter than 4.5 when my SQM reads 18.5.




Here is a link for unihedron
http://unihedron.com/projects/darksky/NELM2BCalc.html

18.5 SQM is 4.4 L.M.
You must have exceptionally sensitive eyesight.


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Tony Flanders
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Re: How Many Messier Objects Are Visible in The City ? new [Re: saemark30]
      #6168560 - 10/31/13 01:45 PM

Quote:

Quote:


For what it's worth, I can see stars considerably fainter than 4.5 when my SQM reads 18.5.




Here is a link for unihedron
http://unihedron.com/projects/darksky/NELM2BCalc.html

18.5 SQM is 4.4 L.M.
You must have exceptionally sensitive eyesight.




No, I don't think my eyesight is exceptional. Better than some, worse than others. I seen people note stars 1/2 mag fainter than I can see while standing right next to them.

I am using averted vision, of course -- really pushing the limit of what I can see.

I have no idea what model Unihedron's calculator is following, but it's obviously very conservative.


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avarakin
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Reged: 07/13/09

Loc: Parsippany NJ, USA
Re: How Many Messier Objects Are Visible in The City ? new [Re: Tony Flanders]
      #6169311 - 10/31/13 09:53 PM

I live in a place with simlar, if not worse, LP - I can only see hints of MW.
Still I can see a lot of objects, including M33. M101 is a different story - I can only see it with averted imagination. I would say I can see about 80% of messiers from my backyard.

Here is a good starting point:
http://www.astroleague.org/al/obsclubs/urban/urban.html

One very simple way to see more stars is to get glasses which are about 0.5 diopters stronger than your original prescription. It is not worth it to pay full price for such pair of glasses, so I normally order such glasses from online retailers.

You may want to get a real telescope instead of binoculars - having additional magnification helps a lot on some objects especially under LP skies.

Alex


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azure1961p
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Reged: 01/17/09

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Re: How Many Messier Objects Are Visible in The City ? new [Re: Tony Flanders]
      #6169408 - 10/31/13 11:06 PM

Quote:

Quote:

Quote:


For what it's worth, I can see stars considerably fainter than 4.5 when my SQM reads 18.5.




Here is a link for unihedron
http://unihedron.com/projects/darksky/NELM2BCalc.html

18.5 SQM is 4.4 L.M.
You must have exceptionally sensitive eyesight.




No, I don't think my eyesight is exceptional. Better than some, worse than others. I seen people note stars 1/2 mag fainter than I can see while standing right next to them.

I am using averted vision, of course -- really pushing the limit of what I can see.

I have no idea what model Unihedron's calculator is following, but it's obviously very conservative.




When
It comes to naked eye magnitude limits I wonder how many folks fall short due to the eyes natural near sightedness in low light as well as astigmatism smearing the stellar point.

I've always found my own naked eye mag limits fluctuate too with prescription and contacts and such. I've always thought NELM was a fair rule of thumb but not always revealing.

Pete


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saemark30
Pooh-Bah


Reged: 02/21/12

Re: How Many Messier Objects Are Visible in The City ? new [Re: azure1961p]
      #6175356 - 11/04/13 12:24 PM

What is the LM through a telescope such as 6" refractor?
I don't think the LM is the same for a SCT or Newt or MCT
with additional mirror coatings and secondary losses.
I'm hoping to see Stephen's Quintet through a 6" achromat.


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uniondrone
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Reged: 12/05/09

Loc: Streetlight Archipelago
Re: How Many Messier Objects Are Visible in The City ? new [Re: saemark30]
      #6179350 - 11/06/13 02:09 PM


I have logged about 60-70 of the Messier Objects from my white zone light-polluted backyard in the Detroit suburbs. I found Tony Flanders' guide (see his post above) to be the best tool available. I copied and pasted the completed table from his website into Excel and sorted by his rating in the U178. I found his assessment to be very good for most objects when using my 10" Dob from my urban site. Anything that he rates as a 1A, 2A, 1B, or 2B was fairly straightforward, if not easy. On a good night, I could find most objects that were rated 3C or better, although some were fairly challenging. Objects with a worse rating were very difficult for me, with most of them not found.


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Ptarmigan
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Loc: Arctic
Re: How Many Messier Objects Are Visible in The City ? [Re: saemark30]
      #6191727 - 11/12/13 10:07 PM

Quote:

What is the LM through a telescope such as 6" refractor?
I don't think the LM is the same for a SCT or Newt or MCT
with additional mirror coatings and secondary losses.
I'm hoping to see Stephen's Quintet through a 6" achromat.




Here is a formula I have seen used.

2+5log(Aperture in millimeters)

2+5log(150) = 12.9
150 mm is 6 inches. The magnitude limit is based on formula given.

However, tinkering with the formula, I can use it to see how faint we can see.

Under urban light polluted sky
1.6+4log(150) = 10.3
Under a light polluted sky in a urban area, the magnitude limit with 6 inch telescope is 10.3

Under perfect conditions
4+5log(150) = 14.9
Under pristine skies, you should be able to see magnitude 14.9 with 6 inch telescope.

These formula are rule of thumb and varies based on optics, magnification, and experience.

Here is a telescope magnitude calculator.
http://www.cruxis.com/scope/limitingmagnitude.htm


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