Perihelion Puzzle

Following on from Mike Dworetsky's Happy Perihelion greetings. . .

I don't know why, but I'd always assumed that Perihelion was on 1st Jan (or
thereabouts). Finding it was today prompted me to find out how it varied
from year to year.

Although I'd expected some 4 year cycle, it seems to be much more variable
than that.

I've posted a plot of the data behind the Perihelion Puzzle link on
www.gwynnefamily.org.uk/astro/

Can anyone explain why it isn't a simple sawtooth over 4 years?

Many thanks

OG wrote:
Can anyone explain why it isn't a simple sawtooth over 4 years?

Presumably the complicated pattern of the sawtooth is a consequence of
perturbation, mostly by the Moon, and the general upward trend is due to
precession of the perihelion..

Best,
Stephen

Remove footfrommouth to reply

--
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+ Stephen Tonkin | ATM Resources; Astro-Tutorials; Astro Books +
+ (N51.162 E0.995) | http://www.astunit.com +
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

"Stephen Tonkin" wrote in message
...
OG wrote:
Can anyone explain why it isn't a simple sawtooth over 4 years?

Presumably the complicated pattern of the sawtooth is a consequence of
perturbation, mostly by the Moon, and the general upward trend is due to
precession of the perihelion..

Best,
Stephen

After posting last night, I had the same thought this morning on the way to
work, but no access to a newsreader.

It seems probable that the perihelion of the Earth/Moon centre of Gravity
would have a constant cycle. The short term variation in the Earth's
perihelion date would then be due to the relative position of the Earth and
Moon wrt the Sun. I also want to explore the issue about precession, because
if perihelion was on Jan 1st in 1970 (according to my old copy of AQ3), we
seem to be looking at a drift of ~ 3 days in 30 years, giving a period of
less than 4000 years.

I'll have to do some playing with the figures to confirm this.

Thx
Owen

"OG" wrote:

It seems probable that the perihelion of the Earth/Moon centre of Gravity
would have a constant cycle. The short term variation in the Earth's
perihelion date would then be due to the relative position of the Earth and
Moon wrt the Sun. I also want to explore the issue about precession, because
if perihelion was on Jan 1st in 1970 (according to my old copy of AQ3), we
seem to be looking at a drift of ~ 3 days in 30 years, giving a period of
less than 4000 years.

I'll have to do some playing with the figures to confirm this.

Thx
Owen

Perihelion makes a 360 degree rotation every 110,000 odd years.

But with equinoxes precessing one way and perihelion the other, I seem
to recall them coinciding every 22,000 calendar years.

--
Martin Frey
http://www.hadastro.org.uk
N 51 02 E 0 47