An Etymological Dictionary of Astronomy and Astrophysics
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The → radius of a → supernova remnant (SNR) when, at the end of the → free expansion phase, the mass of the swept-up → shell equals that of the ejected gas from the → supernova explosion. It is given by R_SW = (3M_e / 4πρ₀)^(1/3), where M_e is the ejected mass and ρ₀ is the initial density of the → interstellar medium.

Sweep, from M.E. swepen, from O.E. swapan "to sweep;" cognate with Ger. schweifen; → up; → radius.

Šo'â', → radius; rubeš, noun from ruftan, rubidan "to sweep," → scan.