What Day Was Yom Kippur in 2017
Yom Kippur in 2017 began at sunset on October 1 and ended at nightfall on October 2. In the Hebrew calendar, it was observed on the 10th day of Tishrei. The dates are determined by a lunisolar calendar that adds a 13th month about every two to three years to keep holidays aligned with their intended seasons. Below are the key details for understanding when Yom Kippur occurred in 2017 and how the Jewish calendar determines these dates.
How the Hebrew Calendar Determines Yom Kippur
Yom Kippur is a fixed date in the Hebrew calendar, always falling on the 10th of Tishrei. The Jewish calendar is lunisolar, meaning it follows the moon but is adjusted to stay in sync with the solar year. A regular year contains 12 months, while a leap year adds a second Adar and a 13th month, shifting the start of Tishrei later relative to the Gregorian calendar. Calculations are based on a 19-year cycle with specific patterns for inserting leap years. Because civil calendars do not align with these rules, the Gregorian date of Yom Kippur changes each year.
Yom Kippur 2017 at a Glance
The table below summarizes the key dates and calendar details for Yom Kippur in 2017.
| Attribute | Verified Detail | Source Type |
|---|---|---|
| Start Date and Time (local) | October 1, 2017, at sunset | Hebrew calendar calculation |
| End Date and Time (local) | October 2, 2017, at nightfall | Hebrew calendar calculation |
| Hebrew Date | 10 Tishrei 5778 | Hebrew calendar year |
| Position in Calendar Year | 10th day of Tishrei; early in the civil year for the Hebrew calendar | Hebrew calendar structure |
| Calendar Type Used | Lunisolar (19-year Metonic cycle with months based on the moon and an embolismic month as needed) | Hebrew calendar rules |
Practical Observance in 2017
On Yom Kippur 2017, observant Jews refrained from work, fasting, and other activities as outlined by Jewish law. Worship services took place on both evenings and the following day, with Kol Nidre recited at the start of the holiday and Neilah near its conclusion. Local sunset and nightfall times varied by location, which affected exact local start and end times. Communities around the world followed the same calendar calculations, even when local clock times differed slightly.
Comparison with Nearby Years
Because the Hebrew calendar shifts relative to the Gregorian calendar, Yom Kippur in nearby years did not fall on the same October dates in 2017. The table below shows how the Gregorian date moves from year to year within a typical cycle.
| Year | Start (sunset) | End (nightfall) | Hebrew Date |
|---|---|---|---|
| 2016 | October 2 | October 3 | 10 Tishrei 5777 |
| 2017 | October 1 | October 2 | 10 Tishrei 5778 |
| 2018 | September 19 | September 20 | 10 Tishrei 5779 |
| 2019 | October 9 | October 10 | 10 Tishrei 5780 |
Key Calendar Rules to Remember
Understanding these rules helps explain why Yom Kippur moves in Gregorian terms each year.
- Tishrei always begins with Rosh Hashanah, which is determined by astronomical calculations and observed sanctification.
- Yom Kippur is fixed at 10 Tishrei, exactly 10 days after Rosh Hashanah.
- A 19-year Metonic cycle includes 7 leap years, in which a second Adar is added and Tishrei is delayed to prevent certain holidays from occurring in the wrong season.
- Postponement rules (dechiyot) can shift Rosh Hashanah by one or two days, which in turn shifts Yom Kippur.
Why Some Years Yom Kippur Is Earlier or Later
The combination of the Metonic cycle, postponement rules, and the shift of Tishrei relative to the equinox explains the range of dates in the Gregorian calendar. In the 21st century, Yom Kippur can begin as early as September 10 or as late as October 10. In 2017, the absence of a postponement and the timing of the Metonic cycle placed it near the beginning of that range.
Summary
Yom Kippur in 2017 was observed from sunset on October 1 to nightfall on October 2, corresponding to 10 Tishrei 5778 in the Hebrew calendar. This date follows predictable rules based on lunar months, the Metonic cycle, and calendar postponements, which cause the Gregorian date to shift each year. While local times for sunset and nightfall vary slightly by location, the calendar day is consistent across Jewish communities worldwide.