Charm of synchronous anniversaries

What are the odds that two anniversaries will fall on the same day? This question popped up in my mind recently after I came across an evocative remembrance note which had been posted on social media by a friend.

The first sentence of the poignant post read: ‘In a strange twist of fate, like Shakespeare, my life partner became a birthday-perisher nine years ago on this day.’ Google informed me that ‘people who die on their birthdays are referred to as birthday-perishers’. I also got to know that statistically, the probability of people dying on their birthday was as low as 1/365 (0.27 per cent). The page also displayed a long list of notable people who died on their birthdays, with Shakespeare at the top.

The citation evoked a medley of synchronous anniversaries in our family. Our daughter was born on the second anniversary of her parents’ marriage. It has been convenient for me to be let off with throwing a single party for double celebrations every year.

A unique case of coinciding anniversaries in our extended family involves the two daughters of my brother-in-law. Their birthday falls on the same day, though they were born seven years apart. Two siblings, who are not twins, having the same date of birth is a rare phenomenon engineered by the law of probability.

Another instance of serendipity is my father’s birthday, which coincided not only with a festive day but also with the birthday of a famous personality. My father was born on Christmas Day, which was also former Prime Minister Atal Bihari Vajpayee’s birthday. Friends and relatives don’t forget to convey greetings on such birthdays which coincide with noteworthy days.

During olden times, the birthday of a person synchronous with a festival was commemorated on the day of the festival. Indian festivals are, however, observed as per specific phases of the moon in the given lunar month. Reckoned with reference to the Gregorian calendar, which is in vogue worldwide now, Indian festivals in successive years fall on different days. Anniversaries are therefore taken as synchronous if they fall on the same day in terms of the Gregorian calendar which has 365 days in a year. Therefore, the odds for two anniversaries to coincide will obviously be one in 365.