SYDNEY -- Leap years happen only every four years, so it's an exciting occasion for those born on February 29 to finally celebrate on their actual day of birth – and perhaps question why leap years even exist.

40-year old Jennifer Williams of Sydney, Nova Scotia, is a Leap Day twin, sharing the date with her brother Adam Young.

On Saturday, she and her sibling, who's currently visiting the United Kingdom, celebrated their proper birth date for the tenth time via a phone call.

"My brother and I always celebrated it together," says Williams. "This year, unfortunately, he's overseas in the U.K. right now.  So, it's a little different this year with him not being around.  But yeah, we always had fun with it."

Williams is also one of four co-workers, who were all surprisingly born on Leap Day. On Saturday, they celebrated their statistically improbable commonality.

"I went all through life hardly knowing anybody that was born on February 29," says co-worker, Corinne MacNeil. "Then to work with three others was… something else."

Why do leap years exist?

So, how and when did leap years become a thing? Well, we have Julius Caesar to thank.

Saint Mary's University observatory director, Dave Lane, explains the idea was first implemented by Caesar in ancient times to account for a slight discrepancy in the earth's annual orbit around the sun.

"So, it's actually pretty close to a quarter of a day off – so 365 and a quarter days," says Lane. "So, that means four times one-quarter, is one day. So, every four years, we have to add a day in order for the fact that the earth doesn't get out of sync."

Essentially, without leap years, we could end up weeks out of sync with the changing seasons.

"The seasons would shift by one day," says Lane. "So, over time, that would accumulate. You could imagine after a century; you might be off a couple of weeks."

Enjoying it for what it is

Meanwhile, those celebrating the extra day are happy to enjoy their actual birthday.

Williams says she'll be bowling with friends and family. Meanwhile, her co-workers have birthday plans as well.

"I have two wonderful cousins that have called and want to take me out to supper," says MacNeil.

"Just celebrate on my real birthday for a change," says Susie MacArthur. "Celebrate with my kids and my family."

Ultimately, while they say they're fine blowing out their candles on February 28 or March 1, Saturday will be just a bit more sentimental.

"I'll be turning 17 tomorrow," says MacNeil jokingly. "Just got my driver's license, four years ago, not old enough to vote yet."