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(fwd) Airmass, extinction and seeing at moderate altitude (h) above the horizon Gianluca Masi asked: Date: Fri, 15 Feb 2002 19:17:50 +0100 From: Gianluca Masi <gianmasi@fr.flashnet.it> Subject: [vsnet-chat 5095] Airmass, extinction and seeing at moderate altitude (h) above the horizon Dear All, I've been trying to find a description of the problems encoutered observing lower than 45above the horizon (h<45ccd, particularly the effect of the airmass in limiting the fantest observable stars with an unfiltered CCD. As a general rule, I have reviewed (in an old message to this list) the formula: X = sec(Z) = 1 / cos(Z) for zenith distance (Z) less than 60 degrees. As I would like to extend this formula to reach h=25 is there a large deviation from it in this range? Also, is the 0.25mag loss per airmass still valid? Also, it is of interest to me to know if there is any formula/comment describing the effect on the seeing of these quite low altitudes; in other words, if at the zenith I have a 1" seeing, what value I can expect looking at h=30 Any comments, personal experiences would be very appreciated. Thank you very much, Gianluca -- *********************************************************************** * Gianluca Masi "Two things fill the soul * * Via Madonna de Loco, 47 with awe and reverence [...]: * * 03023 Ceccano (FR) the starry sky above me and * * ITALY the moral law within me" * * e-mail: gianmasi@fr.flashnet.it * * web: http://www.bellatrixobservatory.org I. Kant * * Minor Planet Center Obs. Code: 470 - Ceccano * * Center for Backyard Astrophysics - Italy * * VSNET Collaboration Team member * * CCD-astrometry-photometry@egroup.com mailing-list moderator * ***********************************************************************
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