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Does this sound right?


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Hello dear friends,

I am a new member of this site. I must say, I find it very entertaining and practical! I was hoping someone could provide me with some information regarding a concern of mine. I am the owner of a 10'' Meade LX200. Now, I noticed that, in the nearby skies of Toronto,Canada, my limiting magnitude for galaxies is about +11. Does this sound about right for a 10'' telescope given the fact that I usually observe near the city?

Kindest Regards,


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The limiting mag of a scope is calculated by the following: -

2.7 + 2.5 x log (Dsquared)

Where D is the diameter of the Apature in mm

I don't have access to scientific calculate to work it out for you.

You need to consider also seeing, transparonly, light pollution etc.

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Those calculators calculate the limiting magnitude in the sense that it is the dimmest star visible near the zenith. If im not mistaken, the limiting magnitude for galaxies would be less than the limiting magnitude for stars since the magnitude given is dispersed over the size of the galaxy, right? For example, its possible to see a 13th magnitude star but not a 13th magnitude galaxy. Is this correct?

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I think that is generally correct although it's dangerous to generalise because then someone who has superbly dark and transparent skies and a well trained eye will then come along and tell you that they have done just that !.

Speaking personally, from my back yard, my 10" newtonian also showed me the same supernova that Russ mentions but I would not be able to detect a 13th magnitude galaxy. Point sources seem easier to spot than diffused ones.

Mind you, if someone would like to transport me and my scope to the top of a mountain in Hawaii then I'd be glad to see if I can "push the envelope" further :)

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You're able to see a SN within M51?? Are we talking about visual observing?? I've observed M51 several times but I have never been able to make out the disk structure.. I suppose its because I observe visually. Are you guys imaging or visually observing? Also, how dark are your skies on the Bortle scale?!

Sam :)

Edited by Vieira314159
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