robjohn
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 May 2 awarded Editor Sep 24 awarded Autobiographer Nov 19 comment rotational oblateness Thanks for your answer. I will have to take some time to digest it. I am also glad that you provided a link to Mark Eichenlaub's question. I will read the answers there as well. Oct 7 comment rotational oblateness I am looking at the first order contributions. Since $\omega^2r/g\doteq0.003433$, approximating the denominator with $g$ rather than $g-\omega^2r\cos^2(\phi)$ will alter the result by at most $0.34\%$. That is much smaller than the difference seen. Oct 7 awarded Commentator Oct 7 comment rotational oblateness I am assuming that $\omega^2r$ is small compared to $g$, not that it is insignificant. If it were insignificant, there would be no oblateness at all. This means that second order terms in $\omega^2r$ will be even smaller compared to $g^2$. Oct 7 comment rotational oblateness I am including the contribution from centrifugal force; that's the $\omega^2r\cos(\phi)$. It is the contribution from the redistribution of mass that I was assuming was negligible. Evidently, it is not. Jul 21 comment rotational oblateness I'm going to assume that there are unstated assumptions in the Wikipedia formula and that the result is affected by the mass redistribution caused by the flattening. If anyone has a more complete answer, or a formula that actually works to compute the oblateness of a rotating planet, I am still interested. Jun 30 comment rotational oblateness @Will: if that were the case, then I would expect the error to be dependent on the density map of the oblate spheroid. The formula in Wikipedia is not specifically for the Earth, yet it is twice what I got, seemingly independent of the density. Jun 29 comment rotational oblateness @WojciechMorawiec: By symmetry, integrating through the southern hemisphere should bring $r_{\text{eq}}$ back to $r_{\text{np}}$. Jun 29 comment rotational oblateness I see that this is related to Why is the Earth so fat?. One possibility for the error in my computation might be the direction of gravity generated by an oblate spheroid. However, this would seem to be dependent on the mass distribution inside the spheroid. The factor of $2$ between my estimate and Wikipedia's seems to discount that the mass distribution would be the cause. Jun 29 awarded Student Jun 29 asked rotational oblateness May 18 awarded Yearling Jan 21 answered What does this quote about the four dimensional divergence of an antisymmetric tensor mean? Dec 11 comment Blue-shifting as opposed to violet-shifting @Kitchi: actually, that plot is "Relative spectral distribution of the uneclipsed or partially eclipsed sky for solar elevation angle less than 51°" The blue responses look to be pretty similar for all plots. Dec 11 comment Blue-shifting as opposed to violet-shifting @Kitchi: Wouldn't the spectral response curve above include the effects of Rayleigh scattering? It is data from a ground-based spectrograph. Some details of the instrument are given in this paper. Dec 11 answered Blue-shifting as opposed to violet-shifting May 19 awarded Teacher May 18 awarded Supporter