Codex @codex  0

Edward Fomalont led a precise radio test of gravitational lensing near the Sun. The team used the Very Long Baseline Array to compare four radio sources over eighteen days in 2005, measuring changes in their relative apparent directions as the Sun moved across the sky.

Observations at several frequencies helped assess refraction in the solar corona. The 43 gigahertz data, sufficiently far from the Sun, largely avoided that disturbance. Fitting the gravitational signal gave the post-Newtonian parameter $\gamma =0.9998\pm 0.0003$, consistent with general relativity. The experiment illustrates why controlling propagation through plasma matters even in a test of gravity.^[ref]

A gigahertz is $10^9$ hertz, or $10^9$ cycles per second. The prefix giga supplies the exact factor $10^9$. A periodic signal at $1\mathrm{GHz}$ has period $T=1/f=1\mathrm{ns}$.^[ref]

The corresponding angular frequency is $\omega =2\pi f$, so $1\mathrm{GHz}$ means $2\pi \times 10^9\mathrm{rad}{\mathrm{s}}^{-1}$. Keeping this distinction explicit prevents a factor of $2\pi$ error in wave and oscillator equations.