Astronomical Visual Limiting Magnitude calculation
Brad Schaefer devised the theory [2000]
and a BASIC program (To the visual
limits, Sky
and Telescope, May 1998, page 97), Larry Bogan translcoded the BASIC
program into a web based JavaScript page and Victor Reijs made a few changes:
- Four bugs have been removed from Bogan's
JavaScript program.
Some of these bugs had major influence on the circumstances
around heliacal events.
Bogan reverted one error back in his web page (accessed on Sep. 11th, 2012 and
Jan 28th, 2021):
KA=KA*Math.pow((1-.32/Math.log(RH/100.0)),1.33)*(1+SL*Math.sin(RA))
should be KA=KA*Math.pow((1-.32/Math.log(RH/100.0)),1.33)*(1+0.33*SL*Math.sin(RA))
This error can cause KA to become 0
(around December), and having such a low KA is not correct.
I have informed him (Oct. 15th, 2016) about this erroneous
reversion, no reaction yet (Jan. 2021).
- Instead of elongation one gives the azimuth compared to the
Object
- Auto calculation of Topocentric altitude
One can give a Goal Magnitude and in that case the object's
topocentric altitude will be calculate in such a way that the
Object becomes just visible.
If this Goal Magnitude=NA, no change to object's topocentric
altitude will be made.
- Extinction angle
By inputting the Object(/star)'s magnitude in Goal Magnitude,
and putting both Moon and Sun well below the horizon (say their
topocentric altitudes at -45 degrees); the script calculates the
Object's topocentric altitude as its topocentric
extinction angle.
A further enhanced JavaScript program is available at this link.
If Goal Magnitude = 99:
The Visual Extinction Magnitude just visible with the unaided eye
is calculated from conditions specified in the form below. This
number depends on the location and phase of the Moon, the location
of Sun, the humidity, your location and height as well as the
Object's topocentric altitude.
If Goal Magnitude <> 99:
The Object's topocentric altitude when just visible with the
unaided eye is calculated from conditions specified in the form
below. This number depends on the location and phase of the Moon,
the location of Sun, the humidity, your location and height as
well as the Goal Magnitude (Magnitude of the Object).
Try various input parameters to observe the effects of each
variable. For more details see the reference sited above.
Intermediate results of astronomical extinction, sky brightness
and air mass are presented in the tables at the bottom.
==============================
FROM "ASTRONOMICAL COMPUTING"
SKY & TELESCOPE, MAY 1998 page 52
'To the Visual Limits'
by Bradley E. Schaefer
=============================
Bogan transcoded to JavaScript and further
corrected and enhanced with the aide of
Victor Reijs
Last major content related changes: May 2, 2003