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"Ahad's constant" - Part (i): magnitude of Milky Way
In this paper:
http://uk.geocities.com/aa_spaceagen...erstellar.html The net, _one number_ solution for the universe's total integrated starlight in visual wavelengths (provisionally dubbed "Ahad's constant") which Abdul Ahad calculated as: Ahad's constant = (magnitude of milky way) + (magnitude of stars) = (-5.0) + (-6.0) = -6.5 mags net (1/300th full moons). Part (i) (magnitude of Milky Way), he estimated at -5.0 using these assumptions: "The Milky Way galaxy's absolute magnitude, accepted in most official journals as an astronomical constant, is -20.5. That figure is based on the assumption that the *entire* galaxy is viewed face on, as one integrated object, from a standard distance of 10 parsecs (32.6 light years). Now, since we are located in one of the spiral arms of the Milky Way not far from the galactic plane and only get an "edge-on view" looking inwards towards the centre of the Milky Way, we see only 50% of the galaxy's total brightness stretching across the night sky (since the remaining 50% is on the *other side* of the dense galactic core, and not directly in view to us). Now, the standard formula for evaluating the brightness ratio, R, between any two objects of magnitudes M1 and M2 is given by:- R = 10^[0.4*(M1-M2)] Hence, this formula can be used to "reduce" the Milky Way galaxy's total absolute magnitude of -20.5 by 50% to give a figure of -19.7, representing the "portion" that we see stretching across our night sky. Since we are located at a distance, d, of about 8,200 parsecs from the galactic centre [Source: Handbook of the British Astronomical Association], the apparent magnitude, m, of the bulk of this "portion" can be calculated from:- m = M - [5 - 5 * log10(d)] = -19.7 - [5 - 5 * log10 (8200)] = - 5.1 Hence, the net integrated magnitude of the "visible" Milky Way stretching across our night skies ought to be about -5.1. However, there are various dark, intervening clouds of interstellar gas and dust, such as the "Cygnus Rift", the "Coal Sack" near Crux, many dark clouds in Sagittarius looking towards the centre of the galaxy, etc. which contribute to dimming the overall light reaching Earth from the broader Milky Way. Hence, if one makes a 10% (0.1-magnitude) allowance for light extinctions owing to such obscuring interstellar media, one will arrive at a net magnitude of -5.0. This would be one way that I would *analytically* estimate the Milky Way's total integrated brightness as -5.0 magnitudes. This figure of course relates to a full 360-degree view of the whole Milky Way. In actual practice, from a particular location on the Earth's surface, only a fraction of this total brightness will be experienced by an observer depending on various factors such as how low the horizons are, which particular quadrant of the galaxy is on view (e.g. the Cygnus region is much brighter than the Auriga region), airglow and light extinctions due to the Earth's own atmosphere which depends on the observer's elevation above mean sea level, etc..." - Abdul Ahad. Now Robert Rowland on uk.sci.astronomy writes: It's reasonable overall but I have an issue with this --- if one makes a 10% (0.1-magnitude) allowance for light extinctions owing to such obscuring interstellar media, one will arrive at a net magnitude of -5.0. Why only 10% light-blotting? Why not 20%? Its far too arbitrary in my view, unless someone else has another thought? I expect Abdul Ahad is pursuing journal entries, so they should put him right. As an _approximation_ it's fine. Is there any views here in the moderated forum? Is -5.0 and the method he uses _reasonable_ as an approximation in Ahad's constant calculation? Uncle Jav |
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Jav wrote:
In this paper: http://uk.geocities.com/aa_spaceagen...erstellar.html The net, _one number_ solution for the universe's total integrated starlight in visual wavelengths (provisionally dubbed "Ahad's constant") which Abdul Ahad calculated as: Ahad's constant = (magnitude of milky way) + (magnitude of stars) = (-5.0) + (-6.0) = -6.5 mags net (1/300th full moons). Part (i) (magnitude of Milky Way), he estimated at -5.0 using these assumptions: [snip] Ahad's constant = (magnitude of milky way) + (magnitude of stars) = (-5.0) + (-6.0) = -6.5 mags net (1/300th full moons). It's reasonable overall but I have an issue with this --- Robert wrote: if one makes a 10% (0.1-magnitude) allowance for light extinctions owing to such obscuring interstellar media, one will arrive at a net magnitude of -5.0. Why only 10% light-blotting? Why not 20%? Its far too arbitrary in my view, unless someone else has another thought? I expect Abdul Ahad is pursuing journal entries, so they should put him right. As an _approximation_ it's fine. So if AC is defining one number for total light from all corners of all galaxies, and Ahad constant = - 6.5 is "right", then was Olbers paradox "wrong"? This link has a few poss. solutions: http://math.ucr.edu/home/baez/physic...GR/olbers.html If Olbers paradox is right, then Ahad's constant should be equal to "infinity" not -6.5. So why is Ahad's constant a limiting magnitude? Anyone else have any thought on this,please. Its rather intriguing! cheres!!! S-S |
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Is there any views here in the moderated forum? Is -5.0 and the
method he uses _reasonable_ as an approximation in Ahad's constant calculation? I did point out it's fine for an approximation. AC will not be a hard scientific constant unless you get it exposed to a photometric device drifting in the oort cloud - way way outside Sol's light domination. Rob |
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You're confusing the issue. Olbers paradox is not about_right_ or
_wrong_ and you already have some answers in your own thread// http://tinyurl.com/3s4th Ahad's constant has a _finite_ value because the increase in light from fainter stars will tail off as you go lower and lower in magnitude. So below a threshold of 15th or 20th magnitude, the nature of Logarathims means the contribution becomes negligible, so AC equates toward a bottom value of around -6.5 (1/300th full moon). Robert |
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