Visual limit value in Quick Info - how is it calculated?

weathermansweden Oct 23 8:34 AM

Hello,I tried to figure out how this works.Does Guide use Brad Schaefers
formulae without mathematical modifications?And where can I get the
algorithm? When trying the original program by Schaefer I get different
I used as an example the 10th of September 2004 at 05:15:00 Central
European Time (MEZ) seen from Ratzeburg in northern Germany (53.71n,
10.77e, height 20m). As Temperature I used 18.3 degrees (65F) and 60%
humidity.I was interested in the near conjunction of Mercury and
Regulus. Were Mercury and Regulus visible for the naked eye?
Using Guide the Visual limit is 0.69 (sun -4.7 degrees below horizon,
Mercury 10.7 above) a realistic value that says – Mercury could be
seen but not Regulus.
When using the program given in Sky and Telescope with the same
circumstances I get about -1.53 as a visual limit – the same result
that comes from Astronomical Visual Limits
when using the same parameters. That means none of both objects could
bee seen by naked eye.
When using the algorithm on the websiteVisual Limiting Magnitude
that also should build on the same algorithm from Schaefer the result is
1.76 (experience 6, age 43, snellen-ratio 1.0) – meaning both
objects could be seen in sky.
My experience and observations speak for the result of Guide –
Mercury could be seen in the morning sky but Regulus was to faint for
being seen with the naked eye.
Therefore I am interested how Guide is calculating the value.

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