Quote:
Originally Posted by OzStarGazer
Starry Night says it has an apparent magnitude of 9.5, do it should definitely be visible through an 8" dob. I even want to give it a go with my 5" dob one of these days...  |
A little note of caution about "apparent magnitude". It is very different from 'visual magnitude'.
This refers to the entire light from the combined surface area of
extended objects, not the actual visual magnitude that a point source is, like a star. So for a given apparent magnitude, the larger the object, the fainter the actual image will be as the apparent magnitude is spread out over a large area.
The apparent magnitude of the LMC is nearly as bright as Sirius. But the brightness that we actually see it at is no where near as bright as Sirius. Like wise with ALL extended objects.
This can mean that some objects are very, very, very difficult to actually see. Two such examples are the galaxy M33 and the Rosette Nebula, NGC 2244. Both are very big objects, M33 the size of the full Moon, the Rosette three times the Moon's diameter. M33's apparent magnitude is 5, the Rosette's 9. While both are relatively bright, through a scope they are extremely faint due to their large size spreading out their light so much.
"Apparent magnitude" is a loaded gun for the unwary. You need to take into account the size of the object, and not confuse it with 'visual magnitude'.
Likewise, the Sombrero will not appear as a magnitude 9, 9.5 object. It will actually appear dimmer, which is why it is hard to pin down.