Mike Brown is an astronomer, and in my opinion is mainly responsible for kick-starting the demotion of Pluto as a planet — he and his team found Eris, an object in the outer solar system that was apparently bigger than Pluto. It was this discovery which set in motion the events that led to the foofooraw about Pluto, and the vote that turned it (and Eris and many others) into "dwarf planets".
Mike continues to observe Eris and other dwarf planets (as well as search for new ones). These objects are small and far away — did you know our own Moon is substantially larger than Pluto? — and therefore hard to analyze. Even with huge telescopes, these objects are hardly more than dots.
However, a fortuitous event landed in the laps of astronomers recently: Eris passed directly in front of a faint star. To us on the ground, it appeared as if the star winked out as the dwarf planet passed in front of it. By carefully timing the duration of this mini-eclipse, the size of Eris could be estimated.
And, to everyone’s shock, Eris looks to be roughly the same size as Pluto. Mike describes all this on his blog.
What does this mean for Pluto? Read More