NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sun sights during an eclipse: "bad limb" calculation
From: Paul Hirose
Date: 2023 Oct 15, 13:44 -0700
From: Paul Hirose
Date: 2023 Oct 15, 13:44 -0700
On 10/14/2023 3:41 PM, NavList Community wrote: > * same for the Moon : 1828.476". Here it goes to 1828.477" possibly > because of some closure rate. I did not understand why there should be a difference, but I think Kermit has the explanation. Topocentric distance to the Moon is decreasing at this time. Therefore, if angular diameter from Horizons (in refracted mode) includes the additional light time due to the atmosphere, the apparent Moon distance is greater compared to airless mode. That is consistent with the Moon diameters Geoff reported: 1828.477 airless vs. 1828.476 refracted. The contraction of the limbs due to refraction is enormously greater: 0.6" Moon and 0.5" Sun, in the direction of the other body. If I ignore that, but include the decrease in center to center distance due to refraction, I duplicate Geoff's refracted contact times. But if refraction is applied to the limbs and body centers, contact times are identical to an airless computation. -- Paul Hirose sofajpl.com
