0
Not a bug
typo on https://www.hebcal.com/holidays/2020
Asara b'Tevet has two dates, one (I think) in error
Answer
Answer
Not a bug
Although the Tenth of Tevet is an annual observance on the Jewish calendar, its placement around the end of the Gregorian calendar year means that in some Gregorian years, there is no observance of the fast, while in other years, the fast is observed twice. Thus, the Tenth of Tevet does not occur at all in 2019. Instead, the "2019" observance of the fast will take place in January 2020, while the subsequent observance will occur in December 2020
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Although the Tenth of Tevet is an annual observance on the Jewish calendar, its placement around the end of the Gregorian calendar year means that in some Gregorian years, there is no observance of the fast, while in other years, the fast is observed twice. Thus, the Tenth of Tevet does not occur at all in 2019. Instead, the "2019" observance of the fast will take place in January 2020, while the subsequent observance will occur in December 2020