Magnitude Test

[GreyRaptor]

Hi all, I am returning to Visual Observing after a number of years without a scope.  I will be testing a new scope over the next week and I wondered if anybody knew of a collection of stars that served as a good test of the scopes magnitude.  What I am thinking of is a group of stars near Polaris with a Mag 2 star, a Mag 3 star, a Mag 4 star.......  This will give me an idea of what I can resolve with the scope from my light polluted back yard.  If not near Polaris, does anybody know of other targets that will work without pointing the scope all over the place (no GoTo)?  Thank you for your help and any advice.  

[Peter Drew]

The "bowl" of Ursa Minor is composed of approximately mag 2, 3, 4 and 5 stars but these are generally a test for naked eye visibility. Any telescope worthy of its name should do much better than that. What size telescope are you considering?

[GreyRaptor]

The scope is a Celestron Inspire 100AZ.  100mm Aperture, 660mm Focal Length.  

[Stu]

How about looking at M45, the Seven Sisters? Plenty of different magnitude stars to see in there, if you download Stellarium or similar you should be able to identify them.

[mikeDnight]

On 25/10/2016 at 23:27, GreyRaptor said:

The scope is a Celestron Inspire 100AZ.  100mm Aperture, 660mm Focal Length.  

If your skies are clear in the early evening you should still be able to catch a reasonable view of the ring nebula M57 in Lyra. In a 100mm scope you should be able to detect a tiny point of light very close to the outer edge of the nebula. You don't need high power for this, in fact a medium power that gives a reasonably dark sky background should be ideal. You may however have to persevere, waiting for your eyes to become dark adapted. When overhead this 13.2 magnitude star is easy in a 100mm scope and should still be relatively easy now with patience. If the Celestron Inspire 100AZ detects this star, then it's as good as you can expect from any 4" telescope.

Another good test object/objects are the E and F stars in the Trapezium at the core of M42. Though not dim, these stars are a challenge due to the proximity of the brighter A and C stars of the Trapezium and are a good test for a 100mm scope. Both E and F are 11th magnitude though F may be more challenging. Patience and a steady atmosphere will pay off with these two stars, but too high a magnification could wipe them out. Around X60 to X70 should be a good power in your 4"! 

Mike.

 

[VilleM]

You can just calculate your limiting magnitude: http://www.cruxis.com/scope/limitingmagnitude.htm
100mm scope at 70x magnification, expert 30yo observer and clean optics gives theoretical magnitude limit of 13.7.

In real life, where observing conditions arent always ideal you can drop 0.5-1 magnitude out of that. Also it makes huge diffrence what youre looking at, if surface brightness is low it might be way harder to see than it should be. For example M33, wich is easy once you have seen it. Before that its very easy to overlook and expect something brighter.

-V

[alan potts]

Just to give you some idea of how conditions change, take M33 already mentioned. Last night I could bearly see it with my 70mm piggyback mounted APO which rides on the 12 inch SC, I have seen this naked eye before from the exact same place, bearing in mine the observatory doesn't move.

Alan