... sky

The wind half-opening angle, $\theta_{\rm max}$, is related to the angle to the plane of the sky, $\alpha$, by $\tan\theta_{\rm max} = (R-1)/(R+1) \tan\alpha$ where R is the ratio (in algebraic value) of maximum to minimum radial velocities in a given lobe. In HH212, $v_{\rm max} > 10$ km s^-1, $-2<v_{\rm min} <0$ km s^-1, and $\alpha=4\hbox{$^\circ$ }$ yield R<-5 and $\theta_{\rm max} = 4\hbox{$^\circ$ }{-}6\hbox{$^\circ$ }$.

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.