New answers tagged

1

The half-light radius is the (spherical) radius from which half the electromagnetic power is radiated. Left unqualified it should mean the power in the entire electromagnetic spectrum, but it can also be constrained to cover a specific range of wavelengths. "Deprojected" has a straightforwrd meaning when considering a regular spiral galaxy. If you are ...


4

The vis-viva equation is commonly written like this: $$v^2 = GM\left(\frac{2}{r} - \frac{1}{a}\right)$$. For $r=a(1-e)$: $$v = \sqrt{GM\left(\frac{2}{a(1-e)} - \frac{1}{a}\right)} = \sqrt{GM\frac{1}{a}\left(\frac{2}{1-e}-1\right)} = \sqrt{GM\frac{1}{a}\left(\frac{1+e}{1-e}\right)}$$. The derivation of the vis-viva equation is not at all trivial and ...


Top 50 recent answers are included