[colechristensen]

>planets are orbiting around center of gravity, which is outside of sun..

The only planet with a barycenter with the sun outside it's radius is Jupiter. And that only slightly. (with an altitude of 0.07 of the sun's radius)

The earth-sun barycenter is 0.0006 times the sun's radius from it's _center_

[jkot]

Heresy! There is only one true barycenter in solar system! :-)

[jahnu]

Even then the definition of the surface is different than the definition of the surface of, say, the Earth, so I'm not sure what "outside" the Sun means precisely.

[ekianjo]

The sun is roughly a sphere of a fixed size. What is there not to understand ?

[jahnu]

Plenty as it happens. Look up the definition of the surface of a star. It's not as simple or intuitive as one would expect.

[lojack]

I believe he's referring to the "fixed size" part of it, really only an argument a true pedant would make.

[jahnu]

Pedant? Or maybe just making conversation about the interesting differences between human experience and understanding of terms and what definitions astronomers use. Why do so many people on HN react as if every comment is a competition?