Friday the 13th
It’s inevitable. Any common year of 365 days – that starts on a Wednesday – has a solitary Friday the 13th and it’s in the month of June. Since 2025 started on a Wednesday and 2025 has 365 days, our sole Friday the 13th in 2025 is in June.
By the way, any calendar month that starts on a Sunday harbors a Friday the 13th. And since June started on a Sunday, we have a Friday the 13th this month.
Previously, the last time a common year sported a Friday the 13th in June was in 2014. Subsequently, after this year’s Friday, June 13, 2025, the next one in June won’t come until June 13, 2031.
In any given year, there’s always at least one Friday the 13th. So, how many Friday the 13ths can we have in a year? The answer is … three.
The last time three Friday the 13ths happened in one year was in 2015 (February, March and November, 2015), and will next take place in 2026 (February, March and November, 2026).
Two Friday the 13ths in a year last occurred in the year 2024 (September and December, 2024). And we’ll have two Friday the 13ths again in 2029 (April and July, 2029).
And other upcoming years with one Friday the 13th are in 2027 (August) and 2028 (October).
The longest period between Friday the 13ths is 14 months and the shortest period is one month between them.
Friggatriskaidekaphobia
Not that we at EarthSky suffer from friggatriskaidekaphobia – an irrational fear of Friday the 13th – but there are lots of coincidences involving the calendar and Friday the 13th!
For instance, last year’s first Friday the 13th – which fell on September 13, 2024, happened exactly 39 (3 x 13) weeks before this year’s only Friday the 13th on June 13, 2025. And last year’s second Friday the 13th – which fell on December 13, 2025, happened exactly 26 weeks (2 x 13) before this year’s June Friday the 13th.
Rhyme and reason of the Friday the 13th cycle
The days of the week realign with calendar dates in predictable cycles. Let’s take the year 2025, and project the matching years for the next 55 years. In other words, we’re looking for common years – one that is not a leap year – and that January 1 falls on a Wednesday. In those years, the only month that begins on Sunday is June.
So the only Friday the 13th that year will recur in the month of June in 6, 17 and 28 years:
Friday, June 13, 2031 (2025 + 6)
Friday, June 13, 2042 (2025 + 17)
Friday, June 13, 2053 (2025 + 28)
But don’t stop there. Continue the series onward:
Friday, June 13, 2059 (2053 + 6)
Friday, June 13, 2070 (2053 + 17)
Friday, June 13, 2081 (2053 + 28)
Friday the 13th in June in a leap year
As we saw above, a common year starting on a Wednesday will always present a solitary Friday the 13th in the month of June. But so will a leap year starting on a Tuesday. This last happened in the year 2008, and will next take place in 2036. Within the confines of a given century, leap year Friday the 13ths repeat on the same calendar dates in periods of 28 years. Thus, it’ll repeat again in June 2064.
Gregorian calendar perturbs the cycle
If the Julian calendar were still in use today, this cycle would continue indefinitely. That’s because the years 2100, 2200 and 2300 are 366-day leap years in the Julian calendar. Yet, by Gregorian calendar rules, these century years (2100, 2200 and 2300) are common years of 365 days. Thus, the year 2100 is a common year of 365 days, and the Friday the 13th cycle is perturbed.
Bottom line: In 2025, there is only one Friday the 13th and it’s in June.
Read more: A year with 13 Friday the 13ths?
The post Friday the 13th comes once this year and it’s in June first appeared on EarthSky.
from EarthSky https://ift.tt/V5bkadE
Friday the 13th
It’s inevitable. Any common year of 365 days – that starts on a Wednesday – has a solitary Friday the 13th and it’s in the month of June. Since 2025 started on a Wednesday and 2025 has 365 days, our sole Friday the 13th in 2025 is in June.
By the way, any calendar month that starts on a Sunday harbors a Friday the 13th. And since June started on a Sunday, we have a Friday the 13th this month.
Previously, the last time a common year sported a Friday the 13th in June was in 2014. Subsequently, after this year’s Friday, June 13, 2025, the next one in June won’t come until June 13, 2031.
In any given year, there’s always at least one Friday the 13th. So, how many Friday the 13ths can we have in a year? The answer is … three.
The last time three Friday the 13ths happened in one year was in 2015 (February, March and November, 2015), and will next take place in 2026 (February, March and November, 2026).
Two Friday the 13ths in a year last occurred in the year 2024 (September and December, 2024). And we’ll have two Friday the 13ths again in 2029 (April and July, 2029).
And other upcoming years with one Friday the 13th are in 2027 (August) and 2028 (October).
The longest period between Friday the 13ths is 14 months and the shortest period is one month between them.
Friggatriskaidekaphobia
Not that we at EarthSky suffer from friggatriskaidekaphobia – an irrational fear of Friday the 13th – but there are lots of coincidences involving the calendar and Friday the 13th!
For instance, last year’s first Friday the 13th – which fell on September 13, 2024, happened exactly 39 (3 x 13) weeks before this year’s only Friday the 13th on June 13, 2025. And last year’s second Friday the 13th – which fell on December 13, 2025, happened exactly 26 weeks (2 x 13) before this year’s June Friday the 13th.
Rhyme and reason of the Friday the 13th cycle
The days of the week realign with calendar dates in predictable cycles. Let’s take the year 2025, and project the matching years for the next 55 years. In other words, we’re looking for common years – one that is not a leap year – and that January 1 falls on a Wednesday. In those years, the only month that begins on Sunday is June.
So the only Friday the 13th that year will recur in the month of June in 6, 17 and 28 years:
Friday, June 13, 2031 (2025 + 6)
Friday, June 13, 2042 (2025 + 17)
Friday, June 13, 2053 (2025 + 28)
But don’t stop there. Continue the series onward:
Friday, June 13, 2059 (2053 + 6)
Friday, June 13, 2070 (2053 + 17)
Friday, June 13, 2081 (2053 + 28)
Friday the 13th in June in a leap year
As we saw above, a common year starting on a Wednesday will always present a solitary Friday the 13th in the month of June. But so will a leap year starting on a Tuesday. This last happened in the year 2008, and will next take place in 2036. Within the confines of a given century, leap year Friday the 13ths repeat on the same calendar dates in periods of 28 years. Thus, it’ll repeat again in June 2064.
Gregorian calendar perturbs the cycle
If the Julian calendar were still in use today, this cycle would continue indefinitely. That’s because the years 2100, 2200 and 2300 are 366-day leap years in the Julian calendar. Yet, by Gregorian calendar rules, these century years (2100, 2200 and 2300) are common years of 365 days. Thus, the year 2100 is a common year of 365 days, and the Friday the 13th cycle is perturbed.
Bottom line: In 2025, there is only one Friday the 13th and it’s in June.
Read more: A year with 13 Friday the 13ths?
The post Friday the 13th comes once this year and it’s in June first appeared on EarthSky.
from EarthSky https://ift.tt/V5bkadE
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