[Laser] photon flux for magnitude 6 stars

[Tim Toast]

Here are some thoughts and figures i got from the web
on photon counts for stars. They might make good
'standard' light sources for testing etc..

On the minimum amount of light detectable by the human
eye under perfect conditions; There seems to be a
general agreement that it's between 5 and 10 photons
'integrated' over a short period of time by the eye.
Single or fewer bunches of photons entering the eye in
that time period are filtered out as 'noise' in the
first layers of the retina. 
The length of time the eye collects or integrates the
light varies from person to person and is normally
between 100 and 250 milliseconds. However, some
persons are able to integrate for longer periods of
time, up to 10 seconds or so, before a reflex in the
brain takes over and stops the process. 
Accordingly on the astronomical magnitude scale, some
people are capable of seeing 2 or even 3 magnitudes
fainter than +6, which is an average for most people
with normal eyesight. A persons age, eyesight, dark
adaptation time, sky conditions and to some extent
'practice' etc.. all factor in to the ability in one
way or another.

Here are some theoretical photon fluxes for 500nm
wavelength light using the formula's at this website:
http://gate.hep.anl.gov/rlt/TrICE/starlight.htm

The Sun (m -26.7) = 3.4 x 10E21 photons/m2 - sec
Sirius (m -1.7) = 3.4 x 10E11 p/m2
Vega (m 0.0) = 7.1 x 10E10 p/m2
m +1 = 2.8 x 10E10 p/m2
m +2 = 1.1 x 10E10 p/m2
m +3 = 4.5 x 10E9 p/m2
m +4 = 1.8 x 10E9 p/m2
m +5 = 7.1 x 10E8 p/m2
m +6 = 2.8 x 10E8 p/m2 28000 photons/cm2
m +7 = 1.1 x 10E8 p/m2 11000 photons/cm2
m +8 = 4.5 x 10E7 p/m2 4500  photons/cm2
m +9 = 1.8 x 10E7 p/m2 1800  photons/cm2
m +10 = 7.1 x 10E6 p/m2 710  photons/cm2
m +15 = 7.1 x 10E4 p/m2 7.1  photons/cm2
m +20 = 7.1 x 10E2 p/m2 .071  photons/cm2

I had assumed there was a close relationship between
the stellar magnitude +6 and that theoretical 5 or 10
photon limit, but after reading up on it and doing
some of the math on the website above, 5 to 10 photons
seems much much weaker than what a magnitude +6 star
shines (28,000 photons per square cm per second???). 
Since the human eye is close to 1 square centimeter in
area when dark adapted, these photon counts seem
insanely high. Could this guy be using the wrong
formula's or constants for this? or my poor math
skills may be showing up. hi

mag. +6 = 
1.1 x 10E-10 watts/m2
or 
1.1 x 10E-14 watts/cm2



F1AVYopto at aol.com wrote:
Does anyone have the precise photon flux value for a
6th magnitude star in a naked eye?
A K3PGP receiver with a 10-15 W/Hz^1/2 NEP range PIN 
photodiode and a 22 cm in diameter mirror gives a
significant scintillation  noise on this stars in good
night conditions. This scintillation noise is
impossible to hear but perfectly visible with Spectran
in the 10 to 100 Hz band. 
Yves F1AVY 
http://pageperso.aol.fr/yvesf1avy/
 



Tim Toast
http://www.aladal.net/toast/exp.html

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