Limiting Magnitude of AM 114eq

[craig1984]

Hi

I have been looking at the messier list and all of their apparent magnitudes. What is the limiting magnitude of my astromaster 114eq?

thanks

craig

[WolfDancer]

The Limiting Stellar Magnitude for your scope is 12.8

More information about your scope specs can be found here
[Registered users can see links. ]

[WolfDancer]

P.S.
Don't forget the stats are for PERFECT conditions.

Its a bit like car manufacturers telling you what the MPG is for your car. Most cars dont get close under normal conditions, but some can exceed them.

[craig1984]

Hi, Thanks very much for the help. I have looked at the list of messier objects and all seem to have a lower magnitude than that. Does that mean that under excellent seeing conditions my 114 should be able to pick them all up?

[WolfDancer]

I'll leave that one for the experts to answer.
I have no idea how much "seeing" affects the view yet. And you'll probably need to be in a proper dark site.

[Krish]

Are there any general formula or something to calculate the limiting stellar magnitude, rather than the info given by the manufacturer? Just being curious.

[swamp thing]

Your scope is very capable of showing the entire Messier catalogue.
Your sky might well stop you though, as some of the low surface brightness ones can be tricky under less than ideal skies.
Good hunting and clear skies
Regards Steve

[jproffitt1]

Originally Posted by swamp thing

Your scope is very capable of showing the entire Messier catalogue.
Your sky might well stop you though, as some of the low surface brightness ones can be tricky under less than ideal skies.

He said it best right there. I have viewed about a third of the messier objects through a 4.5" scope but the seeing conditions will limit you way more than the scope itself.

[kencrowder]

Originally Posted by Krish

Are there any general formula or something to calculate the limiting stellar magnitude, rather than the info given by the manufacturer? Just being curious.

Hi Krish, Yes, and for you it won't be a problem to work out. Some people don't want to do the math.

First start with lm/sr/m^2 at the scope. From the aperture calculate the lm/sr. Work that through the actual fov and apparent fov.

The eye looking at a point source against a black background can detect an 8.5 magnitude point source (1E-09 lm/m^2).

The eye uses an area to compare the point source to the background. I use 3.3E-05 sr. A contrast of 2x is needed.

Magnification spreads the background. So the greater the magnification the closer it comes to black. At some point the apparent background is less than 8.5 magnitude.

Note that for extended objects like galaxies and nebula they are spread also by magnification.

[kencrowder]

Originally Posted by craig1984

Hi

I have been looking at the messier list and all of their apparent magnitudes. What is the limiting magnitude of my astromaster 114eq?

thanks

craig

As said above, 12.8 is your limiting magnitude for a star. However, many of the Messiers are extended sources and the magnitude provided is the total light from an area.

As you go to higher magnitude the background approaches black. At some point your eye becomes the limiting factor. It can only see an 8.5 magnitude star against a black background.

But remember that an extended object like a galaxy is also being spread. So it may not have enough contrast with the background even when the given magnitude is less than 12.8.

Seeing faint galaxies will depend on the sky glow you are dealing with. Since high magnification only makes them bigger and dimmer, sometimes they are more easily detected with low magnification.

Your scope can see them all under very dark skies.