On Sunday afternoon, millions of families in the New York area will sit down to Christmas dinner.
In thousands of those homes, dinner will be interrupted around a quarter past four.
As the sun prepares to set, some man, woman or child will say a brief prayer in Hebrew and light the first candle on the Hanukkah menorah.
This year, for the first time since 1959, the first and typically most festive night of Hanukkah falls on Dec. 25. In the ever-growing ranks of families where Christians and Jews have intermarried, this is more than a mere quirk of the calendar.
For an unabashed syncretist, the double-barreled holiday offers an excuse to eat mashed potatoes and potato latkes in the same sitting, with candy canes and chocolate gelt for dessert. For those who take care to faithfully pass on to their children both their Jewish and Christian heritages, an annual juggling ritual is tricky, and the danger of confusion greater.
But for everyone in a blended family, the phenomenon that has become known as the December Dilemma poses a particular logistical challenge this year.
"How are you going to get everything in?" asked Laurie Rozakis, an English professor at Farmingdale State University on Long Island and author of "The Complete Idiot's Guide to Interfaith Relationships." "You've got your time constraints. You play dreidel, you make latkes, you light a menorah, you've already killed two hours. What happens if you also go to Mass?"
The Cirkers of Port Washington on Long Island - Sarah, Seth and their two children - will attend a Christmas Eve service at a Lutheran church in Florida, where Ms. Cirker's family lives. Morning will mean presents under the Christmas tree.
"Then we'll probably eat a lot of cookies and go catch a plane," Ms. Cirker said. If all goes as planned, they will arrive home in time for Mr. Cirker, who is Jewish, to light the menorah.
The intermarriage rate has been rising steadily since the 1970's, according to the United Jewish Communities' National Jewish Population Survey. As of 2001, about 31 percent of married Jews in the United States had non-Jewish spouses. For Jews who have married since 1995, the intermarriage rate approaches 50 percent.
Fred Berman, an actor in Manhattan, said he planned to pack a menorah for the first Christmas feast at his Italian Catholic in-laws' house since he was married in May. "I don't think I would just throw it on the table and be, like, 'Behold the mighty menorah,' but I think they would understand," Mr. Berman said hopefully.
Some see in this year's confluence of celebrations the opportunity for commerce. Ron Gompertz, proprietor of chrismukkah.com - named for a "holiday" featured on a 2003 episode of "The O.C." - said that when he realized that this year would be "the mother of all Chrismukkahs," he was inspired to publish a Chrismukkah cookbook. Featured recipes include a gingerbread mensch and Rabbi Reuben's bread pudding.
(Even Mr. Gompertz, who also sells interdenominational knickknacks like ornaments depicting dreidels adorned with Christmas trees, has his limits. He vetoed a recipe for gefilte ham after deciding that good taste, in both senses of the word, would not be well served by it.)
For some families, the combined holiday actually works to their advantage. "It's great to be able to stretch out the day with Hanukkah, so that there's not this big orgy of gift opening on Christmas morning," said Annie Modessit, a nonpracticing Methodist knitting designer in South Orange, N.J., who is married to a Jew.
Craig Schatzman, a court employee in Brooklyn, said his Jewish parents had decided to forgo their annual Christmas trip to Atlantic City to start Hanukkah with their offspring. "I think it's great," Mr. Schatzman, 31, said from the apartment in Bensonhurst - where the menorah sits on a pedestal beside the Christmas tree - that he shares with his Catholic wife. "It's like our relationship, melding the two religions together."
For interfaith couples who are more observant, though, trying to honor Christmas and Hanukkah on the same day is a recipe for stress, said Sheila Gordon, the president of Interfaith Community, an educational organization.
"They are two very different holidays that have in common only the timing and that it's very dark so there are lots of candles," Ms. Gordon said. To put it simply, Christmas celebrates the birth of the founder of Christianity, while Hanukkah marks a battle that Jews fought against non-Jews for freedom to practice their religion.
"These issues should not be resolved with a Santa Claus yarmulke," Ms. Gordon said.
Even couples who nominally belong to the same religion can find room to differ. Batia Zumwalt, a behavioral therapist who lives in Hoboken, N.J., was born to Jewish parents and considers herself Jewish, but loves her Christmas tree. Her husband, Andrew Edlin, a gallery owner in Chelsea, refers to the tree as "the big sell-out" and added, "All the people who have murdered us over the years have Christmas trees."
Mr. Edlin said that his plan for this year, like all years, is to "swallow hard and do the best I can."
Ms. Zumwalt said that while she is not crazy about Hanukkah, come Christmas day, "with a smile on a face and a candle in my hand, I will say, 'Come on kids, the sun's going down, let's do it.' "