Why is April 3 different from all other nights? On this night, Conservative, Orthodox and some Reconstructionist Jews outside Israel will sit down to their second Passover seder, while Reform and Israeli Jews will eat as on any other night of the holiday.
That's longstanding tradition. But stirring the pot are some younger American Jews returning from Israel programs, who want to cast off their longer Diaspora observance and adopt Israeli practice in solidarity with the Jewish state.
"You come back, you're slightly shell-shocked, and you're trying to hold onto what you experienced there," said Rabbi Kenneth Brander, dean of the Center for the Jewish Future at Yeshiva University.
"It's not just Passover in particular, it's all the other holidays that you celebrate for just one night in Israel," said Jennifer Trebbin, 23, who spent last year in Israel with Project Otzma, a 10-month volunteer program for recent college graduates.
For the first time, Trebbin celebrated Passover for seven days instead of eight, and attended just one seder.
"Personally, I like it," she said. "There's something about doing it the Israeli way that feels right."
The differing practices go back more than 2,000 years to Jerusalem, when the festival dates were declared by the Sanhedrin, the community's legal body, according to when they sighted the new moon.
As it took time for messengers to reach Diaspora communities with that report, a yom tov sheni, or "second festival day," was added to biblical festivals outside Israel to ensure that Jews there observed at least part of each festival on the correct day.
The extra Diaspora day was preserved even after the institution of a fixed calendar, with the Talmud declaring that Sukkot and Passover be observed for eight days, Shavuot and Rosh Hashanah for two.
Yom Kippur was not extended because of the burden of fasting, and Rosh Hashanah is celebrated for two days even in Israel because it falls on the new moon, instead of mid-month like other festivals.
In the 19th century, Reform leaders in America abandoned the extra festival day, declaring they did not accept the concept of being in exile. Most Reform Jews today understand their shorter observance as being in line with Israeli practice.
Orthodox Jews keep the extra days.
Brander said that in his 20 years as a pulpit rabbi, he's had to sit down "on a regular basis" with young returnees from Israel. He shows them the Jewish sources, and explains that Jews in the Diaspora "aren't in control of their destiny and can lose their calendar at any moment," as happened in the concentration camps and in the Soviet Union.
Most Conservative Jews also keep the extra festival days, despite a 1960s' ruling by the movement's Rabbinical Assembly permitting them to change their practice.
Rabbi Paul Drazen, program development officer for the United Synagogue of Conservative Judaism, said that he is not aware of any congregations that have followed that ruling.
Rabbi Shai Gluskin, director of publishing and online resources for the Jewish Reconstructionist Federation, said most Reconstructionist Jews observe Passover for seven days, considering the extra day an archaic custom rendered unnecessary by modern technology. But they also usually observe two seders, he said.
That's "a deeply held, long tradition in the American Jewish community," said Gluskin, whereas the eight-day custom doesn't have the same pull. "In Reconstructionism, we're not looking for legal consistency," he said.
Ayal Robkin, 21, on the Orthodox track of Young Judaea's Year Course, said that ideologically, he favors a day-and-a-half festival, keeping the negative commandments on that second day, such as not driving, but not the positive ones, like doing a second seder.
Until halachah is changed, however, he will continue with Orthodox custom: "There's a commandment, don't separate yourself from the community."
Sue Fishkoff is a correspondent for the Jewish Telegraphic Agency.