Nov. 28 marks Thanksgiving Day this year, as well as the first day of Hanukkah. Dana Gitell was one of many who took note of the once-in-a-lifetime overlap.

A marketing professional in Norwood, Mass., Gitell coined and trademarked the word “Thanksgivukkah,” launched a website as well as Facebook and Twitter pages and partnered with Judaica retailer ModernTribe.com on a line of T-shirts and greeting cards to mark the occasion — one that, according to one analysis of the Jewish and Gregorian calendars, won’t occur again for more than 75,000 years.

Modern Tribe reworked a Woodstock image for this Thanksgivukkah T-shirt.

Gitell, who had known Thanksgivukkah was coming for five years, said the more she thought about it, the more she came to appreciate the significance be-hind the overlap of two holidays that “both celebrate religious freedom” and have “similar themes.”

“You can celebrate Judaism, you can celebrate America, and you celebrate the Jewish American experience on the same day, because how would this be possible if we didn’t have a country as free and as welcoming as America?” said Gitell.

Exactly how rare is Thanksgivukkah? Extremely — in fact, it’s never happened before, and won’t happen again.

Hanukkah did fall on the last Thursday in November in 1861. But Thanksgiving didn’t yet exist as a national holiday — President Abraham Lincoln only declared it such in 1863.

And looking forward, the synchronicity doesn’t repeat. Jonathan Mizrahi, who has a Ph.D. in physics from the University of Maryland and works for Sandia National Laboratories in Albuquerque, N.M., used the math software program Mathematica to chart the futures of the Jewish and Gregorian calendars, and the output “produced no results other than this year.”

“I thought I made an error in the program, and I checked what I’d done, and everything seemed OK, and I pushed the year out further and further and further … and it still was telling me that it wasn’t ever going to happen,” Mizrahi said.

According to Mizrahi, the Jewish calendar “is very slowly getting out of sync with the solar calendar, at a rate of four days per 1,000 years.”

As the Jewish calendar drifts forward, he wrote, eventually the earliest that Hanukkah will fall is Nov. 29. The final time that Hanukkah will fall on Nov. 28 will be in 2146 — and that will be a Monday, not Thanksgiving.

If the Jewish calendar is never modified, he continued, then it will slowly move forward through the entire Gregorian calendar, until it loops back to where it is now. And Hanukkah will again fall on Thursday, Nov. 28, which will be Thanksgiving … in the year 79811.

On the other hand, Thanksgivukkah can occur more often if you take the first night rather than the first day of Hanukkah as an indicator. This year, the first candles of Hanukkah are lit the night of Nov. 27, while the first full day of the holiday is Nov. 28, corresponding with Thanksgiving.

According to Eli Lansey, who has a Ph.D. in physics from the City University of New York, the first night of Hanukkah will correspond with Thanksgiving in the years 2070 and 2165 — much sooner than 79,811, the next time Thanksgiving will fall on the first day of Hanukkah.

No matter what metric one uses, Thanksgivukkah has garnered a significant following; Mizrahi’s mathematical analysis garnered about 100,000 page views online, to his “utter amazement.”

Gitell also has been surprised by the enthusiasm her projects are garnering.

After creating the Thanksgivukkah Facebook page with her sister Deborah, Gitell worked with graphic illustrator Kim DeMarco to design T-shirts and greeting cards. She said she got an email response from ModernTribe.com within five minutes of sending an inquiry about being the retailer.

The Thanksgivukkah merchandise employs the slogan “Light, Liberty, & Latkes.” Ten percent of proceeds will benefit the nonprofit Jewish hunger program Mazon.

Gitell likens Thanksgivukkah to other once-in-a-lifetime events, like Woodstock.

“We can tell our kids, ‘I was there, I lived through Thanksgivukkah,’” she said. “So that gave me the idea for something akin to a concert T-shirt, expressing that you were there, you lived through it, as a memento.”

J. staff contributed to this report