It dawned on me that book characters have birthdays, too. In Mac on Fireball, the soap opera I'm putting out as a blog, Lt Bugalu's birthday is August 2. He was born on Earth, so he knows that.
People born on a colony - whether planet, space station or even space-faring ship - don't necessarily have the same calendar to work with. Gaelund, which is where Mac was born, not only has slightly more gravity, but a slightly longer year. She reached legal age (of 18 Earth years) to sign up to join the Fleet when she was 16.5 Gaelund years old.
On Gaelund, she knew when her birthday was. But when she reached the Academy, which works on the Earth calendar, she was informed that Sept 17 was her Earth birth date. So at the Academy, and on any Fleet ship she works on, her birthday is on that date.
But she is a Gaelunder, and sometimes she feels affronted to be 'aging' faster than everybody else from her home world. When she first reached the Fireball, she was 27.75 Earth years old, but only 25.6 Gaelund years. Maybe it is this too-speedy aging that makes her somewhat reluctant to celebrate her 'birthday' by this time.
Or possibly - since she won't talk about her earlier assignments, this is pure speculation on Bugalu's part - her birthday offered an obligation to accept gifts from crew members - and officers - that she didn't want to accept.
Whatever her feelings about her birthday, while she is in the Fleet, Mac celebrates on a date that has no noticeable correspondence to the date she was born on the Gaelund calendar. At the Academy, the early fall date didn't feel anything like the early spring date she knew as her 'real' birthdate. It may be easier on a ship, where there are no seasons. Or maybe not, since the calendar is not the one she grew up with.
What about you? If you were suddenly told your birthdate was now Korbalco 33rd, and you were a few years older than you thought you were, would you be inclined to celebrate that date or not?