Quoted from the IOTA Web site:

On the night of 5/6 August 2006, the newly discovered Pluto satellite Hydra (alias 2005/P1) will occult a star, 2UCAC 26034796, with magnitudes respectively

mK = 12.7 , mH = 12.9, mJ = 13.7, mI =14.8, (rUCAC = 16.2) mV = 16.5.

This rare event might be seen from somewhere in Spain, Portugal (00h04), or Canary Islands (00h05), or Africa and South America (00h13). The faintness of the star requires a large enough telescope and a sensitive camera. The star and Hydra will be about 3 arcsec south of Pluto (mK = 12.9, mV = 13.9) : it is a MUST to resolve the images of Pluto and the star on different pixels.

Depending on Hydra's albedo (m = 22.9), the satellite brightness implies a diameter ranging from 50 to 150 km, i.e. a poorly constrained size. Observing such occultation would provide constraints on the satellite size, an important step in determining its albedo, hence its nature (bright icy body vs dark cometary material) and origin. Size can also constrain Hydra's mass, with important consequences for better estimating its resonant interaction with Nix (see under).

http://www.iota-es.de/hydra.html