I realized last week that strictly speaking, even if you're celebrating your birthday in the same time zone that you were born, a birthday doesn't always occur on the same date every year. Let's say I was born at 7 am on Aug 28th. It takes 365 days and 6 hours for the earth to go around the sun. On the next year, assuming it's not a leap year, the anniversary of my birth would be Aug 28th at 1 pm because it takes 6 hours more than 365 days to reach the position on the earth's orbit around the sun when I was born.
Now in a leap year after Feb 29th, the position of the earth with respect to the Sun for a given date and time is a 24 hours ahead of what it would've been if it wasn't a leap year. So, if I was born in 1959 and it's 1960 (a leap year), the anniversary of my birth occurs on Aug 27th at 1 pm, not Aug 28th at 1 pm. The next year (1961) it's Aug 27th at 7 pm, the year after that it's Aug 28th at 1 am, the year after that it's Aug 28 at 7 am, and then the pattern repeats. Since 2012 was a leap year, then in 2011 I had the same birthday I did in 1959 (Aug 27th at 7 am). 2013 is the year after a leap year, so this year my birthday was as in 1961, Aug 27th (at 7 pm).
Now say I was born on Aug 28th at 7 pm in 1961, the year after a leap year, then in 1962 my birthday would be Aug 29th (at 1 am), in 1963 it would be Aug 29th (at 7 am), and in 1964 (a leap year) it would be Aug 28th (at 1 pm). In 2013 it would be like 1962, Aug 29th (at 1 am).
If I was born Aug 28 at 7 pm in 1959, then in 1960 the anniversary of my birth would be Aug 28th at 1 am, the next year Aug 28th at 7 am, the next Aug 28th at 1 pm, and then back to Aug 28th at 7 pm. So, you're not always lucky enough to have more than one birthday, but on the other hand, this kind of birthday could be called a strong birthday.
