Answer:
All days have the same length, everywhere on earth, namely, 24 hours.
If you're asking about the longest period of time that the sun stays up, that's going to
depend on where you are on earth. Here's a quick, rough summary. These descriptions
assume that there's no air on earth ... air makes the sun appear to rise slightly earlier
than it really does, and set slightly later than it really does. But these quick descriptions
will get the point across:
On the equator:
Longest time the sun is up is 12 hours. Twice a year . . . on March 21 and September 21.
Between the equator and 23.5° latitude, north or south:
Longest time the sun is up is 12 hours. Twice a year.
From March 21 to September 21 if north of the equator.
From September 21 to March 21, if South of the equator.
Between 23.5° and 66.5° latitude, north or south:
Longest time the sun is up varies from 12 hours at 23.5, to 24 hours at 66.5 .
24 hours on June 21, if north of the equator.
24 hours on December 21, if south of the equator.
Between 66.5° and 90° latitude (the pole), north or south:
Longest time the sun is up varies from 24 hours at 66.5 to 6 months at the pole.
North of the equator, 24 hours on June 21, March 21-September 21 at the N pole.
South of the equator, 24 hours on December 21, September 21-March 21 at the S pole.