NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Basics of computing sunrise/sunset
From: Frank Reed
Date: 2009 Jun 19, 20:53 -0700
From: Frank Reed
Date: 2009 Jun 19, 20:53 -0700
Christian, you wrote: "But in theory: Assume you know the athmospheric conditions to "the horizon" and beyond right up to GP of the sun, i.e. you are able to monitor these conditions for this entire stretch; say you have an imaginary string of weather balloons thousands of miles long. Would that solve refraction?" Oh yes, I agree with that. This is a simple enough problem in physics. It's just a matter of applying the standard law of refraction to a medium whose density varies continuously with position. If we know the function for the density(x,y,z) exactly from observations, then we can solve the problem by straight-forward numerical integrations, largely thanks to the extremely low cost of modern computing power. What's actually remarkable about astronomical refraction is that basically none of the atmospheric detail matters for angular altitudes above three degrees or so. If you know the local atmospheric density (which depends on temperature and local pressure and to a very small extent on atmospheric composition, humidity, etc.), then you can calculate the refractions for altitudes above three degrees without access to the actual conditions at all points along the line of sight. -FER --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---
