Apparently, it's due to the tilt of the earth's orbital plane and to the ellipticity of the orbit. There are 4 days a year when the correction is zero (since it's a figure 8), and one of them is Christmas. Is this a coincidence? Bill -----Original Message----- From: math-fun-bounces@mailman.xmission.com [mailto:math-fun-bounces@mailman.xmission.com] On Behalf Of Andy Latto Sent: Saturday, December 11, 2010 12:39 PM To: math-fun Subject: Re: [math-fun] Analemma--related question On Sat, Dec 11, 2010 at 2:19 PM, Cordwell, William R <wrcordw@sandia.gov> wrote:
Are clocks set so that noon matches solar noon in the middle of a time zone at aphelion (or perihelion)? I.e., when does the eq. of time give zero correction?
I don't know, but I would guess one of the solstices or equinoxes, rather than aphelion or perihelion. The reason days on earth are more or less than 24 hours is primarily related to the tilt of the earth's axis, rather than the ellipticity of the earth's orbit. The easy way to see this is that on a planet with an axis perpendicular to the plane of its eccentric orbit, the analemma is an oval, while on a planet with a circular orbit and a tilted axis, the analemma is a figure 8. The earth's analemma is a figure-8, with one lobe slightly larger than the other because of the slight eccentricity of the earth's orbit, while the moon's analemma is oval shaped, with some irregularity because the axis of mars is tilted, too. Andy _______________________________________________ math-fun mailing list math-fun@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun