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Charlie HeinAdministrator
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Reged: 11/02/03

Loc: 26.06.08N, +80.23.08W
What’s Up: M 6 and NGC 6416 new
      #5968571 - 07/13/13 06:26 AM

What’s Up: M 6 and NGC 6416

By Steve Coe


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Sarkikos
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Reged: 12/18/07

Loc: Nyctophobia, Maryland, USA
Re: What’s Up: M 6 and NGC 6416 new [Re: Charlie Hein]
      #5968585 - 07/13/13 07:05 AM

Steve,

In this article, you said

Quote:

I am going to assume that if you are reading this then you have had at least some time out under truly dark skies.



Define "truly dark skies."

I routinely see M6 and M7 naked eye at my dark site, which is "only" a yellow zone. I know there are quite a few observers on CN who would not consider a yellow zone to be a dark site. In fact, I read one post in which the CNer lamented that he lives in "only" a yellow zone, and has to drive over an hour to get to a dark site, a gray zone. Poor fella!

Just for the record, my dark site is a yellow zone. But I realize it is not "truly dark."

Mike


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stevecoe
"Astronomical Tourist"
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Reged: 04/24/04

Loc: Arizona, USA
Re: What’s Up: M 6 and NGC 6416 new [Re: Sarkikos]
      #5969937 - 07/14/13 03:10 AM

Mike;

It is possible that the word "truly" was a poor choice, if so, then I apologize.

I use a judging method we invented in the Saguaro Astronomy Club that is a 1 to 10 scale for grading the transparency. So, I don't follow the color scale or the Bortle scale for what is considered dark.

I would say that a dark sky shows the Milky Way as wide and obvious to the naked eye and the zodiacal light can be seen at least 30 degrees above the horizon.

If you are seeing M6 and M7 as naked eye, that is a good site. I would need to observe how much Milky Way you can observe to give it a rating. I traveled to Chiefland, Fla. some years ago and in general the nights were 6 out of 10 for transparency.

I hope that helps;
Steve Coe


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Sarkikos
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Reged: 12/18/07

Loc: Nyctophobia, Maryland, USA
Re: What’s Up: M 6 and NGC 6416 new [Re: stevecoe]
      #5970076 - 07/14/13 08:43 AM

Steve,

For me - and I think most observers - the phrase "dark sky" refers to the level of light pollution at a site. The level of light pollution is typically indicated by color scale, Bortle scale, mags/sq arcsec or naked eye/instrument limiting magnitude. "Transparency" is a transient quality of the atmosphere and is not a good indicator of how dark a site is.

A site can be in the middle of a city, a white zone, Bortle 9, 18 mags/sq arcsec and still be very transparent. I would not be able to see M6 or M7 with my naked eyes at that site - I might not be able to see anything in Scorpius, except maybe Antares - even though it is very transparent on a particular night.

On the other hand, a site can be on a mountaintop at the back of beyond, a black zone, Bortle 1, 22 mags/sq arcsec and have poor transparency on a particular night. At this site, even on a night with poor transparency, I would probably still be able to see M6 and M7 naked eye. (I have never actually been in a black zone, so those who have let me know if I'm wrong here. Remember, I'm talking about transparency of the air, not cloud cover.)

According to the Clear Sky Chart (cleardarksky.com) my dark site is in a yellow zone. There on a transparent night, I easily see M6 and M7 naked eye. On a night with poor transparency, I might not see them.

(My dark site might actually be closer to a green zone, because IIRC, one of my observing buddies saw 21.6 on an SQM meter there. On a transparent night, the "Milkyway shows much dark lane structure with beginnings of faint bulge into Ophiuchus." These are both indicators of green sites on the Clear Sky Chart website.)

Transparency is a transient condition of the atmosphere that can be poor or excellent regardless of the darkness - the light pollution level - of the site.

Mike


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stevecoe
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Reged: 04/24/04

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Re: What’s Up: M 6 and NGC 6416 new [Re: Sarkikos]
      #5970624 - 07/14/13 04:07 PM

Mike;

We might need to agree to disagree here. In SAC we describe transparency as including the amount of cloud cover. I have "light cirrus clouds" in my notes on nights when I rated the transparency as 5 out of 10. This rating system has been in place for over 30 years and so there are lots of folks with notes that use this system. It does provide some consistency, I would not know how to match that system to the electronic sky meter numbers.

I hope that helps;
Steve Coe


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Sarkikos
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Reged: 12/18/07

Loc: Nyctophobia, Maryland, USA
Re: What’s Up: M 6 and NGC 6416 new [Re: stevecoe]
      #5971181 - 07/14/13 08:58 PM

Yes, I think we will have to agree to disagree.

Many amateurs habitually check the ClearSkyChart for seeing and transparency predictions for their observing sites. On those prediction charts, transparency is listed as a separate parameter from cloud cover. They are on different rows of the chart. Certainly they are related, as both are based on water vapor present in the atmosphere, but apparently they are not really the same thing, as the predictions for the two are not always in sync.

In any case, a major feature of ClearSkyChart is the "darkness" of the site, in the sense of relative lack of light pollution. A white site can have excellent transparency, and a black site can have poor transparency, and vice versa.

Relative lack of light pollution seemed to be what you meant in your article when you talked about "truly dark skies." I really didn't get the idea that you were talking about some temporary state of the atmosphere, which is what "transparency" is. Are your usual observing sites so "dark" - meaning relatively free of light pollution - that you don't even think about rating sites for their level of light pollution? So you are concerned with the "transparency" on this or that specific night, and not about light pollution at different sites?

Well then I envy you for your "truly dark skies." But I bet when most amateurs see the phrase "truly dark skies," they are thinking about lack of light pollution, not excellent transparency.

Mike


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stevecoe
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Reged: 04/24/04

Loc: Arizona, USA
Re: What’s Up: M 6 and NGC 6416 new [Re: Sarkikos]
      #5971618 - 07/15/13 02:54 AM

Mike;

You are correct in that we mush together cloud cover and lack of light pollution under the term "transparency". We see it as a measure of how clear you can view deep sky objects either naked eye or in the scope.

Steve Coe


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blb
Post Laureate


Reged: 11/25/05

Loc: Piedmont NC
Re: What’s Up: M 6 and NGC 6416 new [Re: stevecoe]
      #5981716 - 07/20/13 04:57 PM

I thoroughly enjoyed the write up about M6 but was saddened after 13 short paragraphs on M6 to find only two sentences about NGC 6416. Not much to say there I guess.
Could have added something like:
Historical observations
Dunlop, James (1827)
James Dunlop discovered this object from Paramatta, New South Wales, and included it as No. 612 in his catalogue of 1827. Using a 9-inch f/12 telescope, he described it as "a cluster of small stars of mixt magnitudes, about 15' diameter, irregular figure."

John Herschel (1847) Cape Observations
Discovered by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "Cluster class VIII of stars 11m; fills field; not rich; stars in zig-zag lines." On a second occassion he called it "Coarse, rich, vL cluster. More than fills field. Stars 8..12m, one of 8m taken."

NGC/IC Dreyer (1888, 1895, 1908)
The NGC calls it "very large, rich and only slightly compressed."

Published comments
Bailey, S.I. (1913)
Bailey, examining a Bruce plate (Harvard Annals, Vol 72, No 2), describes it as "milky way, pretty compressed, diameter 15'."

Trumpler, R.J. (1928)
Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 22' and the class as 3 2 p.

Burnham's Celestial Handbook
Burnham calls this cluster a "sprinkling of star-dust" lying some 50' east of M6.

Sulentic & Tifft (1973)
The RNGC (Sulentic and Tifft 1973) notes that this is a 8.5 mag open cluster.



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Bigdave24
newbie


Reged: 07/12/13

Re: What’s Up: M 6 and NGC 6416 new [Re: Charlie Hein]
      #5982035 - 07/20/13 09:12 PM

Loved reading about these two!


BigDave24...


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stevecoe
"Astronomical Tourist"
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Reged: 04/24/04

Loc: Arizona, USA
Re: What’s Up: M 6 and NGC 6416 new [Re: Bigdave24]
      #5982176 - 07/20/13 11:06 PM

Buddy, I can certainly add in some obserations from the past in future articles. I just need to gather it all up.

Dave, I am always happy to hear from a satisfied "customer".

Clear skies to us all;
Steve Coe


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youngamateur42
Carpal Tunnel
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Reged: 11/21/12

Loc: La Verne, CA
Re: What’s Up: M 6 and NGC 6416 new [Re: stevecoe]
      #5982384 - 07/21/13 02:46 AM

I've seen more than one might think from where I am in La Verne, I don't know about the "zones" and all that, but it's bad. However despite this, I've been able to pick out M8 and M7 on a night with a 1st quarter moon a few days ago. Steve, do you find the same from urban locations? To me, quite a bit can be seen from here, and it's a real treat when I get out to dark skies (but still polluted by standards)

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blb
Post Laureate


Reged: 11/25/05

Loc: Piedmont NC
Re: What’s Up: M 6 and NGC 6416 new [Re: youngamateur42]
      #5982784 - 07/21/13 11:11 AM

Quote:

Buddy, I can certainly add in some obserations from the past in future articles. I just need to gather it all up.



Steve, I generally love your articles. They are well written and informative but to only include a brief two sentence description of an object, with a telescope much larger than most of us have, was not up to your usual standards. It pained me to say anything to someone I respect but I felt that someone should. Sorry.


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stevecoe
"Astronomical Tourist"
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Reged: 04/24/04

Loc: Arizona, USA
Re: What’s Up: M 6 and NGC 6416 [Re: blb]
      #5983085 - 07/21/13 02:15 PM

Buddy, I am in a position where I can't win. People write me and say they are happy to read modern observations with a larger scope and other write to say that they want more observations with a smaller telescope. I am including virtually all the observations that I have and am trying to keep both groups enjoying and reading. All I can do is all I can do.

Youngamateur42, I just don't observe deep sky objects from within the light dome of cities, it is the reason that I drive away from the lights to observe. When I had an observatory within the lights of Phoenix, Az I only did solar system and double stars from my backyard. I understand that lots of folks are stuck with observing from their backyard under poor conditions, but my articles are not going to cover that aspect of viewing the sky. Sorry.

Clear skies to us all;
Steve Coe


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