I heard about WolframAlpha.com last week.  It is a search engine that does all the calculations it can think of for an entry.   It works with Math (it uses the Mathematica engine from Wolfram Research) History, Chemistry, Music, Astronomy, etc.  They have lots of great examples.

I happened to have a fondness for super massive black holes that are at the center of galaxies.  If you enter “18 billion solar masses black hole” then WoflframAlpha spits back lots of data, including the radius.   This happens to be the biggest hole so far according to Wikipedia.   If you note down the radius 10^13 meters, and then enter “Pluto” and “Sedna” as your next search items, you quickly find out that this humongous black hole is bigger than our solar system.  It is over 8 light-hours across!

Check it out…You will be glad you did.

+Graham