system
Given the following post, respond as if you're commenting on Reddit:
human
I'm aware that the earth is not a "sphere", but, rather, a heptoloidal zircosumfered something or another, however, the Sun sure seems to be very nearly spherical to me. Is it or is it not, and why, in either case?
gpt
Earth and the Sun are both oblate spheroids, which means they are spheres squashed along one axis (the rotation axis). The reason for this is ultimately the same in both cases: a spinning ball of stuff will tend toward hydrostatic equilibrium. This means the surface of the ball should be an equipotential surface for an effective potential, which includes gravitational potential, centrifugal potential (arising from the rotation of the ball), and pressure. The latter is much more important for stars than for planets. 

The Sun turns out not to spin very fast, so its oblateness is very close to 1 which means it is very nearly spherical. Indeed, if the Sun were scaled to the size of a beach ball the difference in the polar and equatorial radii would be something like the width of a human hair. Contrast this with a planet like Jupiter that has a rotation period of only about 10 hours, and so the polar and equatorial radii differ by about 7%. The very nearly spherical shape of the Sun is not too surprising actually. You can work out analytically what the oblateness of a star with a given mass, radius, and uniform rotation rate should be. For the Sun it ends up being extremely close to the true value. (The Sun does not rotate uniformly by the way; the rotation rate depends on the latitude.)