Google does semantic search

Search google for Apparent magnitude of jupiter and you'll get

Jupiter — Apparent Magnitude: 1.6 to -2.94
According to http://www.answers.com/topic/jupiter - More sources »

It means, google understands semantic tagging, see Wikipedia page about Jupiter. Look on info box on the right.

Better example: supernova type of sn 1987a

SN 1987A — Supernova Type: Type II-P (Unusual)
According to http://en.wikipedia.org/wiki/SN_1987A 

Update: New semantic search just started- WolframAlpha