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>> 16-th mag with this telescope [10cm aperture]
>> This is not possible....
>> a magnitude of 7.6 for a Vega type star just detectable
>> ...Which becomes magnitude 13.4 for a 4" aperture.
Alas, this is wrong, too, mainly since it ignores using high
magnifications which makes the background darker. Even the naked-eye limit
from 'true-dark' sites is in the early 8s, around V=8.2 plus or minus
a couple tenths.
No, I don't believe the mag. 16 with 10cm aperture either. At high
power, something like 150x or so with this aperture, the V limit will be
between 14.5 and 15. Seeing has to be good, of course, to get this faint,
probably 1" fwhm or better.
Maybe Hasegawa was using B magnitudes (which will be numerically
larger than V magnitudes) for this reckoning. On the other hand, Mike's
seemingly conservative numbers might result from an incorrect transformation
from photon-quanta to V magnitudes, or more likely, the definition of what
constitutes threshold detectability. The latter goes down considerably
with experience, typically being in the 5-10 percent rate for the best
(most patient in this case) observers. If you insist on seeing something
50 percent or even 100 percent of the time viewing it, then sure, the
limit is much brighter. That's not what Hasegawa-san would have been doing,
for sure.
\Brian
Return to the Powerful Daisaku Nogami
vsnet-adm@kusastro.kyoto-u.ac.jp
