[Astro]Re: Earth Orbit Velocity, Apo-Peri-Helion-Center

Jan Hollan
Sat, 8 Sep 2001 21:32:43 +0200 (CEST)

Dear John,

> Dearest Jan (I am not sure if you are male or female),

Jan = John, a female variant would be Jana in Czech

> I was surfing the web when I came across your "no
> iceage" piece.  I was looking for simple facts about
> the orbital dynamics of the earth around the sun.
> Tell me, when is the earth nearest and farthest from
> the sun and at which point is it moving fastest
> angularly.  Do you have a graph based on the 365.254
> day of these parameters.  I'm not sure if I made
> myself clear as I dont know exactly how to ask the
> question.

The question is clear. 

The date of year, when the Earth is in perihelion, nearest the Sun, and
also moves fastest, is January 2 or 3 (3 in leap years) of UTC (Universal
Time Coordinated, called ``GMT'' in past).  It may be January 2 of Hawaii
time or Jan 4 of Japan time.

It will change in future slowly, each 1000 years will the perihelion delay
some 17 days (so it will be Jan 20 in year 3000).
To the farthest point from the Sun, aphelion, comes the Earth half a year
after the perihelion, on July 4 or 5.
I have no graph at hand, perhaps I could make one, maybe in October.
Shouldn't the number read 365.2422 instead of 365.254? Then it would be
the length of a ``tropical'' year / 1 day.

But, as the Earth orbit is quite close to a circle (the excentricity is
and will remain very low, this the reason why no ice age can come soon),
the graph would not be very informative. The perihelion and aphelion
distances differ by less than 3.5 per cent of the mean one. The angular
velocities ratio is twice larger, 1.07.

> de'kuji, díky (from an online dictionary)
> John Martin-Stark (Male, 40)
> 107 Newton Road
> Groton, CT 06340

Rádo se stalo (it was a pleasure).

best regards,

 Thanks to your question, I've found and corrected an error in my
mhonarchiving script, for public archives -- introduced before, when I
repaired index.html for privat archives.... So, I'm obliged.