I was born 1 day after my sibling. Yesterday was my sibling's birthday but today is not my birthday. When is my birthday?
You were born on one side of the international date line and your sibling was born on the other side of the date line.
This means that although you were born 1 day later it may have been either the same day or two days later in terms of the official date - this is a bit like the way if I remember correctly the person going `around the world in 80 days' had an extra day because they went through the date line in a direction to gain a day.
All I can say after that is your poor mother carrying twins then having such a long labour.....
Your birthday is
on the 1st of January.
You were born
in Kiribati, on some of the eastern islands. Your sibling was born on 30th December 1994. On the next day, the time zone for the Line Islands has been changed to UTC+14, to unify the date for the country with the western part, thus skipping one day ahead.
you might have been born on a relativistic spaceship, while the labo(u)r took 1 day local time, more days passed according to Earth calendar. But I consider the first version more likely.
Another calendar irregularity/discontinuity:
Your sibling was born on:
October 4th 1581
You were born on:
October 5th 1581
Yesterday was your sibling's birthday:
October 4th 1582, the last day of the Julian calendar
Today is not your birthday. It is:
October 15th 1582, the first day of the Gregorian calendar. 10 days were deleted in the transition from the Julian to the Gregorian calendar in 1582
In addition to the already mentioned possibilities, your birthday may also be on
December 31st or June 30th, just like your sibling's (I feel bad for the mother, that's a painfully long labour..)
Since Earth's rotation isn't constant, the universal coordinated time drifts away from the mean solar time, which is why
occasionally, a leap second is added, making it possible that your sibling was born at 00:00:00 on such a date, and you were born at 23:59:60, which is exactly 86400 seconds (one day) later,
but you still share the same birthday.
You were both born on a planet with 48 hour days and now live on earth... thus in earth days your birthday is two days past your siblings.
Or how about
You were both born on the east coast, your sibling at 11:55pm, you at 12:05am the next day... You move to sunny California which is three hours earlier. So on west coast time, your sibling was born at 8:55pm and you were born at 9:05am on the same day! So now you and your sibling share the same birthday.
An alternate answer; very similar to the accepted
I was born 1 day after my sibling.
The sibling was born on February 28, asker was born on March 1
Yesterday was my sibling's birthday
Today is a leap day making it February 29. Yesterday is February 28, the siblings birthday
but today is not my birthday.
It's only February 29, the asker's birthday is still a day away
When is my birthday?
As stated, the birthday in March 1
but today is not my birthday.
You were just born