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John Johnson edited The Earth.tex
over 10 years ago
Commit id: 82362f32b2bbd6aa15143448af0614d1fe4d188c
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My most recent frequent-flyer statement says that there are 3000 miles from Boston (BOS) to Los Angeles (LAX). Since planes travel along great circles, this distance $D_{\rm us}$ represents a segment of the Earth's circumference. There are four time zones (three intervals) from Boston to Los Angeles, out of 24, so $D_{\rm us}$ represents 1/8 of the Earth's circumference.
\begin{eqnarray}
C_\oplus = 8 D_{\rm us} a &=&
2\pi R_\oplus \nonumber b \\
R_\oplus b &=&
\frac{8 D_{\rm US}}{2 \pi}
\label{cearth} c
\end{eqnarray}
\item {\it What is the mass of the Earth?}