April 10th is the 100th day of the year.
It is in April. It is the 10th in a normal year and the 9th in a leap year.
Centenary means the 100th anniversay, which would be the 100th year.
April 10th is the 100th day of this year (2009). During leap years, however, the 100th day of those years will occur on April 9th. This type of information is obtained by consulting a Julian calendar - a calendar that shows, besides normal information, the number of days which have elapsed (and usually also how many are remaining) in the current year.
It is a century or a centennial
The 9th of April was the 100th day of the year 2000.
The 100th day of the year 2012 is April 9th (because of a leap year).
In regular years, the 100th day of the year is the 10th of April. In leap years, it's the 9th of April.
The 100th day of the year is April 10, on a normal calendar year, April 9 on a leap year.
April 10th is the 100th day of the year.
April
Oh, dude, the 100th day of a leap year is like April 9th. Leap years have an extra day in February, so you gotta count all those extra days to get to the 100th day. It's not rocket science, but hey, now you know.
The 100 day of the year is either April 10th - or April 9th in a leap year.
It is in April. It is the 10th in a normal year and the 9th in a leap year.
Centenary means the 100th anniversay, which would be the 100th year.
During a year that is not a leap year it is April 10. For leap years it is April 9.
Saturday the 9th of April 2016.