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Wondering if I've got something set wrong
#1
Hello,
I’m reviewing some of my personal viewings of objects with “difficulty” indicators displayed by the system.
For example, on the night of August 20th I easily found Messier M13 with my 10” dob.
Personally of the Messier objects I might consider M13 to be one of the easiest to find.
The system calculated this object as “Detectable” for that night.
Which to me would seem to indicate I might not find it easily – and yet I did.

On the other hand I’ve been trying to view the cat’s eye nebula “NGC 6543” in Draco
I looked for this object 4 different nights without success – even though I know my scope is set right on its location based on star patterns.
Now the system “difficulty” indicator for this object is displayed as “Obvious”.
And that doesn’t make sense to me.

I’ve got the geo-location and time set correctly as much as I can figure.
And I’ve got “seeing” set to “Average” and “Naked Eye” magnitude set to “6”.

On the one hand I’m wondering if its silly for me to be concerned about this
But then again if I’ve got something set incorrectly – I’m forever going to get “difficulty” indicators I’m not sure I can trust.

Any advise is welcome!
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#2
Hi,

Have you actually measured your faintest naked eye star at zenith on a dark night? It is very important for this parameter to be as accurate as possible. So if not, it may help to do so.

Globular clusters are difficult to rate, because like a lot of things, it depends on how you want to rate it. In a small telescope it will be unresolved as a hazy patch of sky. In a larger telescope you are resolving individual stars. This is going to be the case for a 10-inch Dob. So in this case, SkyTools selects a magnitude limit for the stars that will allow you to get a good view of the resolved cluster. This magnitude is used to determine the difficulty. Those stars are what are "detectable." As you can see, this whole process is going to be somewhat subjective. I am working on improving this for globular clusters in ST4 Visual.

As for NGC 6543, it is only 22 arc seconds in diameter. At the lower magnification used for finding you may be mistaking it for a star. At magnitude 8.3, something that compact really is going to be obvious. I suggest trying again and this time try to identify a slightly fuzzy-looking star near the center of the field, and when you suspect you have found it, switch to higher magnification. It should appear non-stellar at that point.

Clear skies,
Greg
Clear skies,
Greg

SkyTools Developer
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#3
[quote pid='2234' dateline='1567457699']
Thanks Greg much!

For naked eye magnitude I typically look for two specific stars near Polaris.
One having a magnitude of 4.24 and the a magnitude of 6.46.
When I can see both without having to use averted vision – I approximate that as a magnitude 6 seeing night.
But that is probably not any where near the accuracy you’re describing – where I believe one checks at zenith for around 25 stars to get a more accurate reading.

I would think the sky at zenith would probably produce a higher mag seeing-value than looking 44 degrees at my two select stars near Polaris.  Do you think it would make all that much difference?

On NGC 6543 I figure I’m not going to actually see this object with less than 150x magnification.
With a 10mm lens I’m at 120x and not seeing it – and with a 6mm lens I’m at 200x and seeing nothing but pure black.
So I assumed my sky was simply not dark enough for me to see that object – even with a 10” scope.
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#4
Hi,

You don't need 25 stars, but you do need to measure it at Zenith. SkyTools assumes the limiting magnitude is at zenith and then calculates what the limiting magnitude is at other altitudes.
Clear skies,
Greg

SkyTools Developer
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#5
(2019-09-02, 10:09 PM)theskyhound Wrote: Hi,

You don't need 25 stars, but you do need to measure it at Zenith. SkyTools assumes the limiting magnitude is at zenith and then calculates what the limiting magnitude is at other altitudes.


Ok, thanks!
I'll give that a try.
Much appreciate Greg!

Awesome software BTW!!
Forgive me for not saying that in advance  - I know it should - cuz it deserves to be said!  :-]
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