Nishmat's Women’s Health and HalachaIn memory of Chaya Mirel bat R' Avraham

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Vesatot and the International Date Line

18 December, 2023


I was in Australia when I got my last 2 periods. I am currently in NY and I am not sure how to calculate the vesatot. Do I just follow the equivalent of the time back home (e.g., if the veset is the Wednesday night / 24 kislev onah in Australia then it’s the same in NY)? Or do I do a different calculation (e.g., follow the actual timing of the onah back in Australia which is 23 Kislev in NY)? Or something else? Thank you!


Thank you for your question. Because you crossed the International Date Line, the different types of vesatot hayamim have different rules.

For the yom hachodesh, you will calculate your veset based when your period began according to the local date in Australia, and observe it according to the local date in New York. So if your period began at night on the 24th of Cheshvan in Australia, your yom hachodesh is Wednesday night the 24th of Kislev in New York.

For the onah beinonit and the veset haflagah, you need to calculate the vesatot based on how many days have elapsed, so the change in the date between New York and Australia is significant. Since you crossed the International Date Line when you flew eastward from Australia to New York, you gained a full day (e.g., if you flew on a Tuesday morning, you saw a complete sunset and sunrise while on the plane and still landed on Tuesday). Therefore, you will observe those vesatot a full day before you noted on your calendar, so that the number of days that have passed since your last period is accurate..

If, based on your period in Australia, your veset haflagah or onah beinonit falls out on Wednesday night the 24th of Kislev, then you should observe Tuesday night the 23rd of Kislev as your veset in New York

We hope this was clear. Please write back with any further questions.

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