There's a particularly fascinating astronomy story today at Mike Brown's Planets blog: it is about how astronomers through the World have been trying to measure Eris' diameter with greater precision that was known so far.
This has been done by measuring the time of the occultation of a star as Eris passed in front of it.
Somewhat surprisingly Eris is in the low range of expected diameters, just about the size of Pluto. However it is known that it is quite more massive, what poses some intriguing questions about why, as Eris is not the only KBO more massive than Pluto.
Anyhow, Mike Brown explains it much better than I could, so go read the original story.
