Planet X: Magnitude (Revisited)

Back on May 15, 2001 there was a discussion on the Magnitude of Planet
X, at  the distance of 9 Sun-Pluto distances and the Zetas described by
the Zetas.  There was discussion that this object should be able to be
seen, even though only about 3 times the size of Pluto as viewed at this
distance and 81 times dimmer in reflecting sunlight than Pluto at this
distance.  A quote from that time:

In Article <4KhN6.3080$WI.546633@typhoon.hawaii.rr.com> David Tholen wrote:
> Nancy Lieder writes:
>> And it appears as a "blob" (i.e. DIFFUSE, not a pin-point) to some.
>
> Actually, it appears as just as much a "blob" as any other star
> suffering from atmospheric turbulence.  The seeing is a
> function of the atmosphere, not the telescope.

If seems that all stars are not alike. ...

Michael L Cunningham wrote:
>> The thing I don't understand is why M31 (with a 3.7 Magnitude)
>> is not visible to the naked eye? Stars with this magnitude are
>> very bright.
>
> It's called "surface brightness" and the total magnitude is
> equivalent to its light coming from a point source such as a
> single star. ... Since M31 is spread out over a full half degree
> of area (full moon covers a half degree of sky) it is actually
> much fainter without optical aid than a 3.7 magnitude point
> source.