Timed to depart in January and end in late April or May, world-cruise schedules are a yearly constant that take advantage of the best weather conditions in both the southern and northern hemispheres. Although temperatures may be a bit cooler during springtime in the Mediterranean, averaging from the low- to mid-60s F, when some ships on world cruises arrive there, crowds are thin, so it is an ideal time of year to see the sights in comfort. Also taken into consideration by the cruise lines are world-class sporting and cultural events; your ship might provide a front-row seat at yachting races that determine the challenger to race against the defender of the America's Cup, or it may arrive at just the right longitude and latitude to witness an incomparable total eclipse of the sun.