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Re: (meteorobs) Light Pollution
Joe's story of Allen Seltzer is certainly very interesting, but may not be
quite as spectacular as it first seems. It is well demonstrated that
people can read text with over 50% accuracy when they identify individual
letters with less than 50% accuracy and arbitrary shapes with even lower
accuracy. This is because and letters, words and sentences only occur in
certain combinations. A combination of several letters, each of which
may have several possibilities, will often only make one valid word,
given the permutations of all the possibilities. When the words are strung
together, even ambiguous words usually only have one choise that makes
sense. Whilst the acuity of Seltzer was probably exceptional, resolution
cannot be measured using words unless you are looking at nonsense words
that don't follow the general structure of consonants and vowels or use
arbitrary symbols rather than letters. I can think of some other
newspapers that might fit the bill!
This effect of pre-existing knowledge can influence acuity and limiting
magnitude. If you know where something is, the signal to noise ratio can
be reduced to make a detection. Again, I'm not saying Seltzer was in any
way cheating, or that he actually *had* pre-existing knowledge of the
positions of the satellites of Jupiter, but such knowledge certainly does
influence the results.
The only way an impressive feat can be truely assessed is if it is done
blind (now that truely would be impressive!). Someone else should pick an
arbitrary part of the sky and the person being tested draw the stars in
that area. The magnitude level at which 50% of the stars are drawn and
50% missing can be taken as the magnitude limit. An IMO field that
someone is well aquainted with would not be a good test. If you know
where the faintest stars are and strain to "see" them, a biased and
possibly incorrect result can be obtained.
Robert H. McNaught
rmn@aaocbn.aaodot gov.au
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