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Naked eye limiting magnitude

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#1 SrAstro

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Posted 12 February 2024 - 10:46 PM

I was doing some astrophotography tonight due to the clouds finally clearing up and decided to hunt the dimmest star I could see (Naked eye) from my deep bortle 9 backyard.

 

I caught a glimpse of HD36646 with averted vision, check multiple times and then made sure there was actually a star there and it matched perfectly in stellarium. This star is magitude 6.4, so now I am left confused, either the light pollution stats for my location are messed up or I have insane eyesight (highly unlikely). I have previously seen the Andromeda galaxy and 9 stars in the pleiades from said backyard so this isn't a one time thing. Any information on this topic would be much appreciated.

 

I live roughly 5 miles from downtown Houston if that helps at all.



#2 siriusandthepup

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Posted 12 February 2024 - 11:08 PM

That clearing line from the cold front just passed through today. The sky behind was beautiful.

 

I say this because you may have had an instance of exceptional transparency. I have encountered such conditions in the past and when it happens the atmospheric scatter (dust in the air, aka light pollution) can be reduced to almost nothing.

 

My occurrence happened in the suburbs - close in to Austin and was amazing. The view of the Pleiades nebula detail has never been repeated in the 30 years since.

 

Most folks have never been lucky enough to witness the effects of exceptional transparency. Until you do, you can't appreciate the amount of "stuff" which we normally view through.

 

waytogo.gif

 

Near San Marcos, TX  - clearing line passed through here earlier today, before it got to you.



#3 rollomonk

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Posted 12 February 2024 - 11:14 PM

If you were able to see 9 stars in the Pleiades, you were viewing down to mag +5.64... very, very impressive for your location. But HD 36646 is twice as dim.... it seems unlikely. Could it have been HR 1861 (+5.34) -- less than 0.1° NW of HD36646 but 3x brighter?



#4 Keith Rivich

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Posted 12 February 2024 - 11:17 PM

I was doing some astrophotography tonight due to the clouds finally clearing up and decided to hunt the dimmest star I could see (Naked eye) from my deep bortle 9 backyard.

 

I caught a glimpse of HD36646 with averted vision, check multiple times and then made sure there was actually a star there and it matched perfectly in stellarium. This star is magitude 6.4, so now I am left confused, either the light pollution stats for my location are messed up or I have insane eyesight (highly unlikely). I have previously seen the Andromeda galaxy and 9 stars in the pleiades from said backyard so this isn't a one time thing. Any information on this topic would be much appreciated.

 

I live roughly 5 miles from downtown Houston if that helps at all.

I challenge this observation! M31, maybe (but still doubtful) . Mag 6.4 star, no. Nine stars in the Pleiades, no. 

 

I'm 25 miles NW of downtown Houston and, while I can see M31 when the transparency is excellent, my NELM is around mag 4.5 and the Pleiades shows the normal six stars. 

 

Or

 

Your vision is extraordinary and I envy your vision!


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#5 SrAstro

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Posted 13 February 2024 - 12:04 AM

If you were able to see 9 stars in the Pleiades, you were viewing down to mag +5.64... very, very impressive for your location. But HD 36646 is twice as dim.... it seems unlikely. Could it have been HR 1861 (+5.34) -- less than 0.1° NW of HD36646 but 3x brighter?

I saw both right next to eachother, 1861 was noticeably brighter obviously and I really had to push it to see hd36646 and even then it was momentary glimpse every few seconds while straining my eyes. The dimmest star that I saw consistently without too much strain was the nearby hd36780.


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#6 SrAstro

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Posted 13 February 2024 - 12:09 AM

I challenge this observation! M31, maybe (but still doubtful) . Mag 6.4 star, no. Nine stars in the Pleiades, no. 

 

I'm 25 miles NW of downtown Houston and, while I can see M31 when the transparency is excellent, my NELM is around mag 4.5 and the Pleiades shows the normal six stars. 

 

Or

 

Your vision is extraordinary and I envy your vision!

M31 and the 9 stars within the pleiades were viewed with 100% certainty, I have absolutely no doubt that I did see them. The mag 6.4 star was right where it was supposed to be according to the flickering point in my vision, the clearest star I could maintain in my vision was about mag 6.09 according to stellarium and it is hd36780. 

 

I am still a teenager, that may have something to do with my viewing ability but I'm not sure, this isn't the norm on most nights. Could be what Siriusandthepup mentioned, transparency was insane tonight.


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#7 astropgr

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Posted 13 February 2024 - 12:21 AM

I'll have to put into question what you're seeing. In bottle 1-2 skies, you'll be able to see down to 6 mag... in bottle 9, the sky brightness is overwhelming the brightness of mag 6 stars. You wouldn't be able to see it naked eye. There is a possibility that some light pollution had been blocked by low lying clouds around you and reducing it's affect of your location, but outside of that, I seriously doubt your observation.
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#8 steveward53

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Posted 13 February 2024 - 01:21 AM

From Bortle 9 sky no .

 

https://astrobackyar...e-bortle-scale/

 

https://www.lightpol...WNpdHkiOjg1fQ==



#9 Redbetter

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Posted 13 February 2024 - 01:52 AM

I'll have to put into question what you're seeing. In bottle 1-2 skies, you'll be able to see down to 6 mag... in bottle 9, the sky brightness is overwhelming the brightness of mag 6 stars. You wouldn't be able to see it naked eye. There is a possibility that some light pollution had been blocked by low lying clouds around you and reducing it's affect of your location, but outside of that, I seriously doubt your observation.

It is Bortle, not "bottle".  And no, 6 mag as a limit is nowhere near correct.  If you can only see down to 6 mag in near pristine skies your uncorrected vision is not good.  I can see past 7.0  in Bortle 4 conditions without correcting for my mild myopia or astigmatism and I am no youngster.  When I was in my late 20's I reached 8 mag in pristine skies, even though I had some myopia and astigmatism even at that time.

 

Having lived in Houston.  I don't know what the OP saw, but I do know that cloud in Houston would make the sky brighter, not darker.  That light pollution all around gets reflected right back at you when there is cloud above, which is why it is so bright even without cloud. 

 

Excellent transparency could help even in otherwise bright sky, but assuming the OP is correct on the ID's, this is likely more about young eyes and visual acuity..  Some folks can pick out dim objects next to very bright ones far better than other people do, and this could be another example of that (dim star on bright background.)  Just because I can't go this dim in such bright sky doesn't mean that nobody else can.  



#10 TheUser

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Posted 13 February 2024 - 04:35 AM

Doesn't it mean that there's Bortle indices not a 9?



#11 Sebastian_Sajaroff

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Posted 13 February 2024 - 05:57 AM

1. Bortle Scale is subjective, depends on the individual. Not everyone has the same visual acuity and training to detect M33, Gegenschein, dim stars, etc. naked eye.

2. Bortle Scale is tied to local conditions (now and here), not to a specific place. A Bortle map makes no sense !

 

A clean transparent New Moon night in the middle of the Atacama desert or the Antarctica plateau can easily be a Bortle 1.

Same spot fourteen days later is Bortle 7-8 at best (Full Moon). 

 

My backyard is usually Bortle 9, I can even read the newspaper outside.

Sometimes, several of my neighbours turn their lights off and I can't read the newspaper anymore, improving my backyard to Bortle 7.5-8.

During COVID-19 lockdown and the latest Quebec power outage (during April 6th 2023 icestorm), conditions improved a lot and enjoyed a solid Bortle 5 sky.


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#12 SrAstro

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Posted 13 February 2024 - 07:59 AM

1. Bortle Scale is subjective, depends on the individual. Not everyone has the same visual acuity and training to detect M33, Gegenschein, dim stars, etc. naked eye.

2. Bortle Scale is tied to local conditions (now and here), not to a specific place. A Bortle map makes no sense !

 

A clean transparent New Moon night in the middle of the Atacama desert or the Antarctica plateau can easily be a Bortle 1.

Same spot fourteen days later is Bortle 7-8 at best (Full Moon). 

 

My backyard is usually Bortle 9, I can even read the newspaper outside.

Sometimes, several of my neighbours turn their lights off and I can't read the newspaper anymore, improving my backyard to Bortle 7.5-8.

During COVID-19 lockdown and the latest Quebec power outage (during April 6th 2023 icestorm), conditions improved a lot and enjoyed a solid Bortle 5 sky.

So it would be correct to say that my conditions dropped to bortle ~6 for me personally?



#13 SrAstro

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Posted 13 February 2024 - 08:03 AM

I'll have to put into question what you're seeing. In bottle 1-2 skies, you'll be able to see down to 6 mag... in bottle 9, the sky brightness is overwhelming the brightness of mag 6 stars. You wouldn't be able to see it naked eye. There is a possibility that some light pollution had been blocked by low lying clouds around you and reducing it's affect of your location, but outside of that, I seriously doubt your observation.

Mag 6 isn't all that dim, from a bortle 4 site I've been to they are quite obvious if you try looking for them. There was not a single cloud in the sky last night.


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#14 Sebastian_Sajaroff

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Posted 13 February 2024 - 09:16 AM

So it would be correct to say that my conditions dropped to bortle ~6 for me personally?


Observing in front of a street light usually means you’re in Bortle 7-8.

#15 KBHornblower

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Posted 13 February 2024 - 10:39 AM

I was doing some astrophotography tonight due to the clouds finally clearing up and decided to hunt the dimmest star I could see (Naked eye) from my deep bortle 9 backyard.

 

I caught a glimpse of HD36646 with averted vision, check multiple times and then made sure there was actually a star there and it matched perfectly in stellarium. This star is magitude 6.4, so now I am left confused, either the light pollution stats for my location are messed up or I have insane eyesight (highly unlikely). I have previously seen the Andromeda galaxy and 9 stars in the pleiades from said backyard so this isn't a one time thing. Any information on this topic would be much appreciated.

 

I live roughly 5 miles from downtown Houston if that helps at all.

Let's assume for the sake of argument that your star identification is accurate.  If we could time-warp Mr. Bortle in his visual prime to being side by side with you last night, he would rate the sky closer to 4 than 9 on his scale.  In his Sky and Telescope article he had his personal naked eye limiting magnitude (NELM) in half-magnitude increments from one class to the next, starting at 7.5 or better in a pristine sky with excellent transparency.  This shows that there is no fixed Bortle class for any given location.  In his text leading up to his presentation of his scale, he included caveats such as saying that NELM is not a reliable absolute indicator, because it varies among observers and can change rapidly in varying atmospheric conditions.  Likewise with visibility of M31 and M33.

 

You were blessed with a rare burst of splendid transparency.  When I was in Houston on a hot, humid summer night I could not see much of anything except the Moon.



#16 TheUser

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Posted 13 February 2024 - 12:41 PM

So it would be correct to say that my conditions dropped to bortle ~6 for me personally?

I'm afraid that "Yes". There's an objects one is capable to observe on the basis of it, as I see the Bortle scale.

 

I put links here not as an advice to educate for someone but as source that could be useful if any.

 

https://en.wikipedia...ki/Bortle_scale

https://skyandtelesc...dark-sky-scale/


Edited by TheUser, 13 February 2024 - 12:42 PM.


#17 SrAstro

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Posted 13 February 2024 - 05:39 PM

Let's assume for the sake of argument that your star identification is accurate.  If we could time-warp Mr. Bortle in his visual prime to being side by side with you last night, he would rate the sky closer to 4 than 9 on his scale.  In his Sky and Telescope article he had his personal naked eye limiting magnitude (NELM) in half-magnitude increments from one class to the next, starting at 7.5 or better in a pristine sky with excellent transparency.  This shows that there is no fixed Bortle class for any given location.  In his text leading up to his presentation of his scale, he included caveats such as saying that NELM is not a reliable absolute indicator, because it varies among observers and can change rapidly in varying atmospheric conditions.  Likewise with visibility of M31 and M33.

 

You were blessed with a rare burst of splendid transparency.  When I was in Houston on a hot, humid summer night I could not see much of anything except the Moon.

Makes sense, as I said this wasn't any normal night, though tonight is looking to be of similar quality (at least according to the forecast)!

 

Based off the criterion on that article, my location fits with bortle 4-5 in terms of NELM and bortle ~7 in terms of wide DSO's like M31. Since it says that diffuse objects will be affected by LP much more than stars and that NELM is dependent on visual acuity, I think it's relatively accurate if we consider my younger eyes and last night's conditions. My normal NELM from here is within the mid 5th magnitude, an average clear night will reveal 32 andromedae (Mag 5.4) barely with averted vision and nothing dimmer, the fact that I was able to go over 2x dimmer is likely due to transparency as you said.



#18 Captain Quark

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Posted 13 February 2024 - 06:49 PM

You have discovered your super power. Can you see Jupiter’s big four moons naked eye?



#19 SrAstro

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Posted 13 February 2024 - 07:07 PM

You have discovered your super power. Can you see Jupiter’s big four moons naked eye?

Haven't thought about trying that!

 

I'll probably need to find something thin enough to hide Jupiter's glare while also not blocking the moons, would that work?



#20 Captain Quark

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Posted 13 February 2024 - 07:18 PM

Haven't thought about trying that!

 

I'll probably need to find something thin enough to hide Jupiter's glare while also not blocking the moons, would that work?

Supposedly, some people can see them just by looking. Not me.



#21 PKDfan

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Posted 13 February 2024 - 07:43 PM

Haven't thought about trying that!

I'll probably need to find something thin enough to hide Jupiter's glare while also not blocking the moons, would that work?


Hi SrAstro !!

Yes totally !! Just try and find a thin pole you can use as an occulting bar and they are easy peasy.

Glaring really is the issue overwhelming the eyes contrast.

I sadly laugh at people who deny others their observations and even deny some outright categorically.

Says much more about the poster than the OP.

I'm in B9 hades and ya know sometimes i see a dozen stars and othertimes hundreds.


TRANSPARENCY rules CONTRAST thresholds.

Remember LP is a backscattering function and has NOTHING to do with a Bortle rating.
And EVERYTHING to do with the amount of junk between you and the target.


Clearest Skies
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#22 SrAstro

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Posted 13 February 2024 - 07:59 PM

Supposedly, some people can see them just by looking. Not me.

Insane, couldn't imagine detecting that unless seeing was just short of perfect.



#23 MEE

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Posted 13 February 2024 - 09:24 PM

If the OP is seeing down to mag 6.4 in Orion, then the Milky Way should be easily visible from overhead down to about 45 degrees above the horizon

Can you see that, @SrAstro?

How long did it take you to see the star? What percentage of the time did you see it? Were there multiple attempts where you did not set it, and only a few that you did? How many times did you glimpse it before you confirmed?
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#24 Keith Rivich

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Posted 13 February 2024 - 10:33 PM

Hi SrAstro !!

Yes totally !! Just try and find a thin pole you can use as an occulting bar and they are easy peasy.

Glaring really is the issue overwhelming the eyes contrast.

I sadly laugh at people who deny others their observations and even deny some outright categorically.

Says much more about the poster than the OP.

I'm in B9 hades and ya know sometimes i see a dozen stars and othertimes hundreds.


TRANSPARENCY rules CONTRAST thresholds.

Remember LP is a backscattering function and has NOTHING to do with a Bortle rating.
And EVERYTHING to do with the amount of junk between you and the target.


Clearest Skies

I'm all for the OP seeing what he saw, but have you ever been 5 miles from the Downtown of the 4th most populated city in the United States? And I am not sure which side the OP is on. If east then he/she is in the middle of the refineries. To the west is the party district, lit up like a Christmas tree. North and south are very dense neighborhoods. The only area I can even consider is around the Memorial Park district. But even there, there is a huge shopping district just a few miles to the SW.

 

This is a very extraordinary observation. 

 

Among my group of observing friends the call for "I challenge that observation" is not a out down, its a call to repeat the observation with other observers, namely us, to verify what was claimed to be seen. 

 

The last time I got challenged was the jet in m87. I showed them! 


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#25 SrAstro

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Posted 13 February 2024 - 10:54 PM

I'm all for the OP seeing what he saw, but have you ever been 5 miles from the Downtown of the 4th most populated city in the United States? And I am not sure which side the OP is on. If east then he/she is in the middle of the refineries. To the west is the party district, lit up like a Christmas tree. North and south are very dense neighborhoods. The only area I can even consider is around the Memorial Park district. But even there, there is a huge shopping district just a few miles to the SW.

 

This is a very extraordinary observation. 

 

Among my group of observing friends the call for "I challenge that observation" is not a out down, its a call to repeat the observation with other observers, namely us, to verify what was claimed to be seen. 

 

The last time I got challenged was the jet in m87. I showed them! 

In the little area to the Southeast around NRG.

 

I tried again tonight, glimpsed it for a moment several times, much more difficult than it was last time and nearly impossible, any observing at all was more difficult, better than normal but still bad. I need another last night sometime soon .

 

This time I was able to see HD37744 (Mag 6.1) without a ridiculous amount of difficulty, completely confident in this observation as it was actually my younger sister who pointed it out and told me to look there. I am very confident that I did indeed see the 6.4 star yesterday as I didn't actually know it existed until I saw it and checked its magnitude through stellarium. 

 

Speaking of observations, how did you go about proving that you saw the m87 jet?




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