What is a Planet?

I got involved with the Pluto debate and more generally with the definition of “planet”. I wrote popular and technical articles on the subject, the latter with “Pluto-killer” Michael Brown (we took opposite sides). Here is a page of musings on this…

Brown Dwarf

As one of the discoverers of brown dwarfs, I wrote both popular and technical reviews of the discovery and the nature of these objects during the early days. The science continues and advances, but here are some of my contributions.


As I’ve taught Intro Astro over the years, we’ve always talked about the likelihood of hearing from aliens, and whether and how we should be listening. The astronomical parts of this question are now fairly resolved, but that leaves a number of other factors we know less and less about. Interestingly, the most influential factor is how long detectable civilizations last on average. Here is my discussion of the Drake equation.