A leap year occurs every four years, with this year set to see an extra day in February.
But what are the traditions surrounding the longer year?
From leap year birthdays to marriage proposals, here’s everything you need to know about leap year traditions.
For many years, it was traditional for men to propose to women - except on 29 February.
Tradition was, and for some still is, that once every four years on 29 February women could ask their loved one to marry them instead.
Where did this tradition come from?
Lonely Planet explains that, “Folklore suggests the tradition began in Ireland in the 5th century, with a deal brokered between St Brigid of Kildare and St Patrick, but the tradition has spread across Europe and beyond.
“In Scotland women intending to propose are advised to wear a red petticoat visible to their love – perhaps to give them fair warning.”
Tradition also stated that any man who refused a Leap Day proposal should be issued with a fine, which could range from money to silk gowns.
It’s said that in Denmark the penalty for a proposal refusal is 12 pairs of gloves.
This is so that “the spurned maiden can wear to hide the ignominy of having no ring, and in Finland a man who declines must provide enough fabric to make a skirt,” adds Lonely Planet.
When do babies born on a leap year celebrate their birthday?
Babies born on February 29 are invited to join The Honor Society of leap year Day Babies.
Leap day babies, who may also be known as leaplings, leapers, or leapsters, still get to celebrate their birthday, but they usually either choose 28 February or 1 March.
Are leap years unlucky?
It’s also known that some in Scotland believe that being born on Leap Day is bad luck, and is compared to Friday 13, which is also believed to be an unlucky day.
It’s also said that some Scottish farmers worry for their livestock, with an old saying of “leap year was never a good sheep year”.
In Greece, it’s believed that if you get married in a leap year, at any time all, then it’s bad luck, with many thinking that it will end in divorce.
What is a leap second?
The International Earth Rotation and Reference Systems Service, which is the organisation that keeps track of the earth’s motion in space, has added an extra ‘leap’ second into the length of a day.
This has occured on 27 occasions since 1972.
It’s said that the reason behind this adjustment is that the gravitational pull of the sun and moon drags on the Earth as it rotates, which then slows it down and lengthens the day.
Although the effect is tiny, it's believed to be significant enough to require adjustments.
The last leap second occurred at midnight on 31 December 2016, bringing the solar day back into alignment with Universal Time.
This is the global standard clock used on the internet, and it’s also used in aviation and for other applications.
However, in comparison to leap years, leap seconds are unpredictable because the Earth’s rotation fluctuates irregularly, in response to weather hot rock churning underground.
The next leap second is expected to happen on 30 June 2020.