Talk:Airmass

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Title says "Airmass", but the text uses "air mass". Make up your mind :). Thue 14:22, 5 Jun 2004 (UTC)

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[edit] Airmass Formulae

Luis, do you have a source for the formula

X =\sec\, z \,(1 - 0.0012 \sec^2 z) ?

This looks very much like Young and Irvine's 1967 formula

X = \sec\,z \,(1 - 0.0012 \,(\sec^2 z - 1)),

except that the term in the inner parentheses is missing a "−1" (adding the term doesn't really help the accuracy much). I'm going to add mention of formulae by Hardie, Young and Irvine, Kasten and Young, Rozenberg, and perhaps a couple of others, and I don't want to duplicate mention of Young and Irvine if that is the one you had intended. JeffConrad 08:03, 29 October 2006 (UTC)

[edit] Edits of 31 October–1 November 2006

I've added several airmass formulae, as well as numerous references. I have assumed that the first correction to the secant formula intended Young and Irvine's 1967 formula, so I have revised it to that form (there is little practical difference).

The formula for airmass at the horizon was added without citing a verifiable source; I have retained it for now, but am inclined to delete it because it does not seem to agree with the accompanying text: for the standard ground temperature of 290 K, the isothermal scale height is approximately 8500 m; using this value and Earth's mean radius of 6371 km, the calculated airmass is 34.3, vs. the accepted value of 38. I fail to see how this can be described as "very good accuracy."

I did not revise the graph to add plots for the additional formulae; I did revise the graph caption to indicate that not all formulae are included. JeffConrad 02:35, 31 October 2006 (UTC)

I've added some material and revised the section on Horizon airmass in attempt to deal with my earlier objection. I've added an External link to Eric Weisstein's article on airmass, which is consistent with my understanding of the topic. I'm not sure it qualifies as a verifiable source, however, so I've added {{Fact}} in a couple of places. I don't have easy access to Young's 1976 chapter that Weisstein cites, so I'm reluctant to vouch for the content. JeffConrad 03:51, 1 November 2006 (UTC)

[edit] Allen's airmass table

Allen's 1976 airmass table isn't really a 'reprint' of Bemporad's 1904 Table XXIII; the latter was far more expansive, giving values for every 0.1° for zenith angles between 60 and 84°, and for every minute of arc for angles between 84° and 89° (the latter the limit of Bemporad's table). Allen credits Bemporad, Schoenberg (1929), and Snell and Heiser (1968) for the data. I am unable to determine where Allen got the values for 89.51° and 90°; however, my ability to pick details from the text of Bemporad and Schoenberg is severely limited because I don't read German. JeffConrad 07:39, 14 May 2007 (UTC)

[edit] Kasten-Young formula

The formula was originally given in terms of altitude γ as

X = \frac{1} { \sin\, \gamma + 0.50572 \,(\gamma + 6.07995^\circ )^{-1.6364}}\;;

in this article, it is given in terms of zenith angle z = 90^\circ - \gamma. JeffConrad 06:40, 10 July 2007 (UTC)

[edit] Font size of Notes

Normally, format changes to notes and references are discussed on the talk page before changes are actually made. Is there a reason other than personal preference to reduce the font size for notes? Although I agree that it's normal practice in paginated material, the benefit is less obvious when substantive footnotes essentially are endnotes. One negative is that the notes may be more difficult for readers, especially those over 40 or so, to read, especially when viewed on high-resolution LCD monitors. JeffConrad 08:23, 22 September 2007 (UTC)