Zada Connaway Author of "Mother's Journals : parts 1, 2 and 3"

For an observer located anywhere within the Solar System - excluding the contribution of light from the Sun (Solar constant) - provisional integrations using stellar magnitude data sourced from astronomical catalogs places an approximation for this constant in the range:

having a mid-point value of -6.5 magnitudes as a consensus within the astronomical community. This is the total integrated brightness of the night sky that we visually experience from Earth.

Mathematical properties and scientific use

The terminating approximation of the above algorithm yields a value of the net amount of natural sky light an observer would visually experience from any desired location in the universe. It thus has real world, universal applicability for modelling the local environment at any given point in space-time. The number itself is not a true ‘constant’, of course; its value would differ, at least infinitesimally, depending on where and when one makes the measurements. Hence, some astronomers prefer to call this phenomenon ‘Ahad’s magnitude’ (see note 2 at the foot of this article).

In mathematical terms, this constant has the properties of being a real and an irrational number, that is computable, though it is both transcendental and asymptotic.

Once determined in magnitude terms via the given algorithm, the value of Ahad’s constant can then be expressed in a variety of other luminous flux measures, such as watts per square meter, or however else one desires. For example, in the vicinity of the Solar System and in local interstellar space, it is of the order of ~ 1/300th of a Full Moon’s worth of light.

In observational astronomy, the algorithm enables one to compute the net contribution of stellar light that would illuminate objects beyond the luminous dominion of the Sun. For example, in the area of telescopic and CCD programs hunting to detect dwarf planetary bodies residing within the Oort cloud, the value of Ahad’s constant would be a measure of the amount of incident light from the surrounding cosmos illuminating such objects that are too far out from the Sun for its flux to have the greatest, or close to overwhelming, contribution to their total surface lighting.

In the fields of deep-sky astronomical scrutiny, such as the observation of dark nebulae in far-off locales within the Milky Way galaxy, which have no intrinsic luminosity of their own, Ahad’s constant enables one to compute the total flux contribution to their illumination from stars and other sources of incandescent light in their surrounding 3D neighborhoods. The observed surface brightness, contrasted against the theoretical surface brightness predicted by Ahad’s algorithm of such molecular clouds, would then hint at core nested unseen protostellar sources, warranting further multispectral investigation.

Ahad Radius and Ahad’s Sphere of the Sun

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At a distance of circa 11,500 astronomical units (0.18 light-year) going radially outward from the Solar System in any chosen direction, the Sun's apparent light output matches Ahad's constant.

It is thus possible to draw an imaginary sphere around the Sun of such a radius, within which the Sun would remain the most supreme source of light, relative to the universe's total background illumination:

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The outer edge of such a sphere, in principle, defines an edge of the Sun's monopoly of light and heat provision to our Solar System and nearby interstellar space; an effective end of its light dominion.

References

1. How bright is the sky beyond our Solar System? A. Ahad, Journl Brit.Astron.Assoc. Vol. 115, No. 5, p. 297

2. The Sky this Week - David Oesper, October 23, 2008

3. Cambridge Encyclopaedia of Stars by James B. Kaler (Cambridge University Press, 2006), p. 50

4. Scientist quantifies the darkness of outer space, The Mathaba News Network, February 1, 2007

 Republished with permission--see links to observe the charts and formulas.