The formation of cis-trans isomers is a consequence of the absence of free rotation. Geometric isomers that only differ from each other in the 3-dimensional arrangement of the substituents in space. They have identical bonding and substituents. Alkane.
What sells out first: Christmas/New Years, Presidents Week in February, Spring Break Week in March, Easter Week and July/August sailings when the children are out of school. To get the space you want on the cruise and necessary air arrangements, don't hesitate to book 9 to 11 months in advance if possible. The remainder of February, March and April sailings usually start to fill up once the weather starts to turn cold in the Northeast and Midwest.
For international flights, you'll want to purchase tickets even farther in advance. Travelers going to Africa should book the earliest, at 166 days in advance, while those heading to the South Pacific can book much closer to their departure, at an average of 70 days in advance.