Crux, Latin for a puzzling or apparently insoluble problem, is another name for the constellation of stars named the Southern Cross, faintly seen (larger than normally visible to the naked eye) on the cover of Lost Key
As Harry Parker explains to Annie in Lost Key, the Southern Cross can be used to locate the south pole if the observer is in the southern latitudes. The celestial south pole is not marked by a single star like the North Star points us to the north pole. The equivalent celestial point in the south is directly in the middle of a black void.
The Southern Cross contains four bright stars so situated that they depict the extremities of a Latin cross and, like all constellations, have gradually migrated across the skies over the millennium that man has watched the stars. In the Biblical days the Southern Cross was just visible at the horizon in the Middle East. It was last seen from the latitude of Jerusalem at the time of Christ. Today it is no longer visible at latitudes north of 25 degrees (the approximate latitude of Key Largo).
The axis formed by the northern and southern most stars in this constellation points toward the South Pole.
The brightest star in the constellation is Acrux at the foot of the cross. Acrux is really a binary pair orbiting each other, but they are so far away that we see them as one star. The other four stars are commonly call Gacrux, Becrux and Dcrux, not surprisingly from the astronomical designations of alpha, beta, delta and gamma as you can see from the diagram. Becrux is actually the brightest single star, but is not as bright as Acrux, the binary pair, the point of the constellation closest to the pole and proximate to a huge dust cloud named the Coal Sack.
Now, for Parker's answer to Annie standing on the open porch of the Blue Parrot bar looking out over the Atlantic - how to tell time: Let the Southern Cross to be the hour hand of a 24 hour clock (24 at the top, 12 at the bottom, 6 and 18 between the two). The South Celestial Pole is the center of the clock. The imaginary clock rotates with the long axis acting as the pointer around Acrux, and the other three acting as an arrowhead pointer to the imaginary twenty-four hour clock face. (And for you purist - yes, I drew the cross bar angle incorrectly, should have been slightly tilted in the opposite direction, but since I was looking at the Cross the long way around, I reversed it by mistake.)
The sighting is exact on March 29th, each year. To correct for dates other than March 29 deduct 2 hours from the sighted time for each month since March 29.
Click here for plans to construct your very own Official Blue Parrot Conch Time Clock.