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Re: star vs planet
if we think it's big enough to burn it's on matter, but isn't doing so? What if it's doing so but only on a very limited basis and doesn't look like a star?

As Jupiter currently does. It emits more radiation than it receives from the Sun. None of it is in visible wavelengths though. Is Jupiter therefore a star?

As Jupiter currently does. It emits more radiation than it receives from the Sun. None of it is in visible wavelengths though. Is Jupiter therefore a star?

So did the earth when it was in its molten state and still would if not for its insulating crust. The point is that Jupiter does not have enough mass to sustain a 4H fusion chain reaction. Of course, matter could accrete slowly enough in a larger object that fusion would never ignite, or so fast in a smaller object that fusion would occur briefly in a smaller object, or that an object would be so hydrogen-poor that fusion would not occur. And many stars no longer have a chain reaction going because their fuel is exhausted. These stars will continue to cool forever until they resemble terresatrial planets except for their mass and density. Some of the lightest of these may even resemble gas giant planets like Jupiter because there is not enough gravity to reduce its outer layer to white dwarf electron degeneracy. So the dividing line between the largest planets and smallest stars is a mathematical calculation of the smallest mass that will create the nuclear confinement to sustain a continuous fusion process, regardless of whether such process is, will or ever had taken place.

"As Jupiter currently does. It emits more radiation than it receives from the Sun. None of it is in visible wavelengths though. Is Jupiter therefore a star?"

Yeah, I thought there was something like that about Jupiter. Under his definitions I think Jupiter is too big to be a planet. There will be ceaseless arguments about what size, what mass, what makeup constitutes a planet.

But it's the small end that really gets me. How do you know when a planet's gravity is stronger than it's material.

His definitions are about the worse I can imagine, and yet he thinks they are concise.