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)

[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 [citation needed] 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)

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