My life goal: finding all NGC objects to magnitude 11.0

[Robstargazer15]

well.it seems imposible, but from my latitude 31* north, 87* west location, it is possible to view objects to -50 declination with atmospheric pressure pending, to find lots and lots of NGC objects. it is crazy but it is always a possibility that i can succeed. the lowest altitude NGC object i found was Omega Centauri. which was easy. so far, i have 41 found since january 1st of 2013. Messier objects don't count, even though they have NGC numbers.

[southernman]

Sounds like a real challenge! You will of course have to venture south to get anything from -50 to -90.

The trip would be worth it though. There is just so much to see 'down here'.

[Mr Q]

What a project! From the list HERE it seems there must be a thousand or more

[Pig]

Can some one please explain the concept of magnitude in astrological terms to me please. IE why is something that is bigger more difficult to see ? I am sure there must be some kind of ratio involved between size, distance, light emission and the ability to detect.

Thank you

[acey]

There are approximately 1000 NGC/IC objects with V-magnitude down to 11.0, and that's certainly an achievable goal (I've observed more than that in the last ten years). The numbers rise steeply as you go to fainter magnitudes.

There's a big north-south imbalance in the NGC (for cosmological reasons) so it's possible for a northern observer to see the vast majority. The professional astronomer Guillaume Bigourdan (1851-1932) observed all the NGCs down to his horizon from Paris Observatory (and measured their positions). It took him over 20 years but in the end he saw more than 6000 objects, out of a total of about 7400 in the NGC. His scope was a 12" refractor.

In modern times, Steve Gottlieb has been observing all the NGCs, and is apparently nearly finished (after about 20 years of observing). Many of his observations are recorded at the NGC/IC project website (most with an 18").

The best site for NGC information is Wolfgang Steinicke's:

http://www.klima-luft.de/steinicke/index_e.htm

His book about the NGC is by far the most comprehensive on the subject:

http://www.amazon.co.uk/Observing-Cataloguing-Nebulae-Star-Clusters/dp/0521192676/

The NGC/IC Project has pages for all the NGC objects which include DSS images:

http://www.ngcicproject.org/

Good luck with your project.

[acey]

Can some one please explain the concept of magnitude in astrological terms to me please. IE why is something that is bigger more difficult to see ? I am sure there must be some kind of ratio involved between size, distance, light emission and the ability to detect.

Thank you

Magnitude corresponds to the photometric quantity called illuminance (or illumination) - the thing you would measure with a lux-meter (a photographer's light meter). As you move further away from the object the illuminance decreases. Illuminance is effectively the amount of visible light arriving from the object to the eye, i.e. the apparent brightness. Move away from a light source and it won't look as bright.

Surface brightness corresponds to the quantity called luminance. If you had a meter to measure this, you would find that as you move further away from the light source, the luminance stays constant. This is because surface brightness is a function of the target's apparent size (its angular area) as well as its magnitude. As you move further away from a target, its light is spread further but its apparent size is also smaller - the two effects cancel and the "magnitude per area" stays constant.

Stars are effectively "point sources" without size so we just talk about their magnitude. Galaxies and nebulae are extended objects, so we talk about both their magnitude ("total brightness") and their surface brightness ("brightness per area").

Surface brightness is what determines the visibility of galaxies and nebulae. A telescope can't increase the surface brightness of a target: if there's not enough contrast against the sky then it will be invisible, no matter what telescope you use.

Hence when choosing DSO targets we should really start by considering surface brightness rather than magnitude. In fact, however, the surface brightnesses of galaxies and nebulae in the NGC are all within the bounds of what can be seen in a dark sky (they were all discovered visually). So the NGC is a good target list for the visual observer - as long as the sky is dark enough - and in most cases (out of 7000-odd objects) magnitude is actually a fairly reasonable guide to the sort of aperture that might be necessary, with 12" being enough to see pretty much everything under the right conditions. (Guillaume Bigourdan did it - see previous post).

Many more galaxies have been discovered photographically, and many of these have very low surface brightness, which is why they escaped visual detection. So for objects not in the NGC, it's a good idea to look at the surface brightness first, and not assume that the magnitude will be a guide to visibility.

All the NGC observers had skies without light pollution, where they could see stars to at least magnitude 6 with the naked eye, and the Milky Way was very clearly visible. That's the kind of sky we need if we want to see what they saw.

[Pig]

Acey thank you very much for the explanation I understand a lot better now. I will also do some further reading