People find leap years inspiring. Perhaps it's the feeling they're getting an extra day. But February 29 is really not an extra day. It just a mathematical attempt to make up for lost time.
Image: picture-alliance/dpa/L. Schulze
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Family lore has it my father was born on February 29, 1936 - a leap day in a leap year many moons ago. It seems fitting for a man who says he's "not interested" in birthdays that he should have the option of missing his three years out of (almost) every four.
But given my dad's talent for spinning yarns (he started his working life in markets), it's possible he wasn't even born in 1936, but in 1935, and that was just a bog-standard, "common" year.
Hold on: what's the difference between a common year and a leap year?
In the Gregorian calendar, one of the most widely used calendars in the world, a common year is your standard "365-day" cycle. A leap year, however, has 366 days. It's an attempt at improving the accuracy of the Western-Christian calendar to keep it in sync with the Earth's rotations around the sun and "fixed" astronomical events, such as the equinoxes and solstices.
Put simply: there's no perfect calendar. A calendar depicts a year, usually an imperfect year.
A year is the time it takes for the Earth to orbit the sun. We say it takes 365 days for the Earth to orbit the sun - but that's not strictly true. A true year - known as a tropical year, solar year, astronomical year or equinoctial year - is the time it takes the sun to pass from vernal (or spring) equinox to vernal equinox. That's 365 days, 5 hours, 48 minutes, and 46 seconds, or 365.2422 days to be precise. So there's roughly a six-hour margin of error in every "common year." Leap years compensate for the extra 0.2422 of a day. Failing to compensate for these "extra" hours would send us out of sync with the seasons - by about 24 days after only 100 years.
A common year is 365 days, which is about a quarter of a day shorter than a tropical year. At 366 days, leap years are three-quarters of a day longer than a tropical year. Over time, the combination of common and leap years keeps us roughly in sync with the Earth's orbit of the sun.
How often do we have leap years?
Leap years occur almost every four years, with some exceptions.
What's this about "almost" every four years?
Leap years were introduced by that grand old Roman, Julius Caesar, in the Julian calendar. Back then, leap years occurred every four years without fail. But it was felt this over-compensated. The Gregorian calendar was then devised by Aloysius Lilius, an Italian astronomer and philosopher, (and named after Pope Gregory XIII) to replace the Julian calendar, with stricter criteria for leap years.
In the Gregorian calendar, leap years are those that can be evenly divided by four — unless they can also be divided by 100, in which case they are not a leap year.
However — and this is an exception to the rule that came into effect in the year 2000 — if a year can be divided by 4 (leap year), 100 (not a leap year), but also 400, then it can be considered a leap year.
We have to skip some leap years to account for the fact that those extra, or decimal hours (the 5 hours, 48 minutes, and 46 seconds) in the tropical year are just short of a quarter day. So in a sense we're re-adjusting the re-adjustment, but we're still left with an imperfect sum.
Battle of the calendars
The Gregorian calendar was first adopted in Italy, Poland, Portugal and Spain in 1582. It is regarded as one of the most accurate calendars in use today. But it maintains a margin of error of about 27 seconds per year - that's one day in every 3236 years. It's fourth in line for accuracy behind the Mayan calendar from about 2000 B.C.E. (margin of error: one day in every 6500 years), the Revised Julian Calendar from 1923 (margin of error: one day in every 31,250 years), and the Iranian Solar Hijri calendar from the 2nd millennium B.C.E. (margin of error: one day in 110,000 years). The Solar Hijri is said to achieve its high accuracy by using astronomical observations rather than mathematical ones.
Do other calendars have leap years?
Yes. The Chinese calendar has leap years featuring leap months - rather than leap days as in the Gregorian. A Hindu leap year also features an extra month. The Ethiopian calendar has 13 months, where the 13th month has five days in a common year and six in a leap year. The Islamic leap year occurs 11 times in a 30-year cycle. And a Jewish leap year has between 383 and 385 days, occurring seven times in a 19-year cycle.
And does all this leaping do us any good?
We do a fair bit of leaping about - even adjusting Universal Time with leap seconds to account for irregular changes in the Earth's rotation. It can be very important for people to feel they are in sync with time and astronomical events, for instance, for religious reasons, such as Easter, which is tied to the Spring Equinox. But if not for religious or, say, environmental reasons, does it really matter if the seasons drift from month to month, or if we lose hours and days over thousands of years? Would we even notice?
Midsummer — the year's longest day and shortest night
All over Europe, people celebrate Midsummer's Day, set on June 24 in Germany. The summer solstice already played an important role in ancient traditions and customs, from Scandinavia to Spain.
Image: AP
The midsummer 'white nights'
It seems that the summer solstice has always fascinated people. The year's longest day is an important holiday, especially in Nordic countries. During those days, the nights there never become completely dark as the midsummer sun creates the famous "white nights." Pictured above is a lake in the Finnish part of Lapland at around midnight.
Image: picture-alliance/chromorange/O. Borchert
A typically Swedish tradition
"Midsommar": that's how the Swedes call the festivities they celebrate on Midsummer's Day, which is always set on a Saturday between June 20 and 26. City dwellers set off to the countryside to take part in the fun with dances, singing and music. Special foods and alcoholic drinks are served. Most Swedes, however, have ceased to believe in dancing elves, trolls and the magical powers of dew.
Image: picture-alliance/dpa
Dancing around the midsummer tree
Following Christmas, Midsummer's Day is the year's second important holiday in Sweden. Burning bonfires is an important element of the festivities in different countries. But in Sweden, there are also other customs. Among them, a slender tree trunk, decorated with leaves, flowers and garlands is erected on the eve of Midsummer's Day, and people dance around it.
Image: picture-alliance/dpa
Getting married on Midsummer's Day
Not only in Sweden, but also in neighboring Finland, Midsummer's Day is a popular wedding date. The Finnish couple pictured above celebrates its wedding on the island Seursaari in Helsinki, which is a popular holiday resort. Maybe lovers believe that saying yes on the year's longest day guarantees them a long and happy life together.
Image: imago/Xinhua
Head decorations
Customs don't have borders. Scandinavians and Slavs seem to share quite a few of them. Like in Sweden and the Baltic countries, women and girls in Belarus create flower garlands for the midsummer festivities. They decorate their heads with wreaths made of flowers and branches. This tradition is said to be of pagan origin. The plants used are believed to have special healing powers.
Image: Reuters/G. Garanich
Pagan traditions were Christianized
Solstice traditions go back to very ancient ages — some go back to the late Neolithic. It's believed that already in those early times, people burnt huge bonfires which were seen as a symbol for light and survival. The tradition was then taken over by the Christian religion which gave it a new interpretation. In many countries, the day is now called St. John's Day, celebrated on June 24.
Image: picture-alliance/dpa/P. Seeger
A feast celebrated by many Christian countries
During the first centuries A.D., the Julian calendar determined the date of the summer solstice. Celebrated on June 24, it was designated as the feast day of John the Baptist. Its observance starts the evening before, known as St. John's Eve. The Bible mentions that Jesus' cousin was conceived six months before Christ, whose birth is celebrated on December 25.
Image: Reuters/v. Fedosenko
Remaining pagan rites
Pagan rites still come into play when people across Europe ignite their bonfires on St. John's Eve. In Belarus, people celebrate what is called there Kupala Night by singing and dancing before jumping over fires. People believe that this act would purify them from their sins while strengthening their health.
Image: Reuters/G. Garanich
Fire and traditional costumes
Wearing Bavarian traditional clothes, this boy is standing in front of a St. John's fire in Upper Bavaria. Like in Sweden, Belarus and Ukraine, traditional customs are part of the festivities in Germany. The festivities also make everyone aware of one fact: From now on, days will become shorter again.
Image: picture-alliance/dpa/S. Jansen
Straw puppets against evil forces
Summer solstice bonfires are believed to contain magical powers that help people get through the upcoming cold season. In some locations, people try to increase the effect. In Lower Bavaria, for example, people bind a straw puppet on the stack of wood below the fire that will then burn down. It's believed to drive evil spirits away.
Image: picture-alliance/dpa/A. Weigel
The fire of love
Some lovers seem to believe that summer solstice fires can strengthen or revive their love. The couple pictured above is kissing in front of a St. John's fire on Kandel Mountain in the southern part of the Black Forest. The flames on the mountain top are clearly visible from far away.
Image: picture-alliance/dpa/P. Seeger
Beach parties in Spain
In Spain, people living close to the coast prefer to celebrate St. John's Eve on the beach, including those of Gijon in northern Spain, Alicante and Valencia (pictured). In some places, people all jump into the ocean at midnight to welcome the summer solstice.
Image: picture-alliance/dpa
The morning after in Valencia
The bonfires on the Mediterranean beach of Valencia, Spain's third largest city, draw thousands of people. People hang out, sing and dance together with their families, friends, and neighbors. However, the morning after the party, the beach is littered with plastic bags and empty bottles.
Image: picture-alliance/dpa
Historical atmosphere
The Neolithic cult site of Stonehenge in southern England is believed to be at least 5,000 years old. It marked the points where the sun rose and set. In recent years, up to 36,000 people have been gathering to celebrate the summer solstice. Europe's biggest unorganized festivity of this kind, it also attracts numerous members of neo-pagan and esoteric groups clad in historical outfits.
Image: picture-alliance/empics/B. Birchall
Rocks full of mystery
A popular location for summer solstice celebrations in Germany, the rock formation pictured above, called the Externsteine, is found in the eastern part of Westphalia. The rocks are believed to have attracted up to 10,000 people already 12,000 years ago. The Nazis promoted the site as part of their cult of Germanic myths, which is why neo-Nazis and neo-Pagans are among those who celebrate there.
