Tony Flanders' Astronomy Site
Views of M31
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m31.gif

These pictures show M31 and M32 at identical magnifications through two different telescopes at two different levels of light pollution.  The magnification is nearly optimal for the smaller scope, but a higher magnification brings out somewhat more detail in the bigger scope.  However, even at this fairly modest magnification, M31 is spilling out of the NE corner of the field as seen in the suburbs.
 
As you can see, M31 is affected much more by light pollution than by aperture; this is typical of galaxies.  Under urban skies, only the bright core is clearly visible, although the 178mm Dob brings out a faint extension to the SW.  A considerable portion of the disk is visible under good suburban skies, although this is still only a tiny fraction of the entire galaxy.  Under dark skies, M31 fills more than half the field from top to bottom, and extends far out of the field on the SW and the NE.