Guest Lecture On Planets By Carl Brusse
We didn't record the lecture on Thursday 27 February, because it was a guest lecture and the logistics of recording it were too hard.


Carl Brusse gave almost exactly the same lecture last year, and we DID record that. It's at




A new dwarf planet has been discovered, check it out at

Despite the inordinate amount of time that was spent on finally settling whether Pluto was a planet or not, I think a rigorous definition of any word that is used in science is vital. The eventual definition, however, included two clauses (one which was relevant to geophysics and the other which was relevant to orbital dynamics) which all of the eight planets satisfy, making one of these clauses redundant and the definition a bit sloppy. On another note, I think distinguishing between planets and exoplanets is a pretty clear violation of the Copernican principle, even if it is only nomenclature.

Also, I thought it was pretty neat how the meaning of the word planet has transformed over the history of astronomy from meaning 'something that moved in the sky', to 'something that orbits the centre'.

Joss Kirk

Carl tells me that the accidental distinction between planets and explanets was really just a joke. If you read the definition in context, it's not really restricting the definition of "planet" to solar planet.