A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2021 Jan 2, 07:07 -0800
Dave, what are the last couple of columns in the table you posted? Is this output from JPL Horizons? I assume that the column with numbers starting with 0.9832... represents the Earth-Sun distance. With 14 digits past the decimal point, that seems to indicate precision beyond reality.
Could you check something for us (well, for me!): how much time passes from the best estimate of the instant of perihelion until the mean distance of the Earth from the Sun has increased by, let's say, one mile? And how much time until the mean Earth-Sun distance has increased by the diameter of the Earth (so that the daily rotational change in distance is smaller than the cumulative Earth-Sun change in distance)? I'm curious what the numbers mean when people announce --as certain social media did this year-- the exact instant of perihelion. It seems like it may be a tricky thing to define... How long is the Earth "at" perihelion?