Of course, the Gregorian calendar is a solar based calendar. The earth orbits the sun in about 365.25 days. So the Gregorian calendar is 365 days long with a leap year day about every 4th year added on February 29th. (Note: Be suspicious whenever I use a term like "about" 365.35, and "about" every 4th year, because it usually means there are even more complexities to calendar making.) The Jewish calendar is a lunar based calendar but also has some machinations thrown in to make sure that the Passover holiday will always fall in the spring. (By comparison, the Islamic calendar is only lunar based and therefore the great fast days of Ramadan fall in a cycle throughout the year.)
A local rabbi at Chabad ran a calculation on his computer taking into account the basics of these two calendars and the facts that Thanksgiving always falls on the 4th Thursday of November and Hanukkah always falls on the 25th day of the month of Kislev of the Jewish calendar. Using strictly these calculations we would have another coincidence of the two holidays in 2070 and again in 2165. However, indeed as I alluded to, there are other machinations of both calendars to consider. The solar year is really 365.2425 days long. By the time of Pope Gregory XIII in 1582, those 11 extra minutes had added up so that calculations to determine Easter had put it out of the springtime. The date number for the spring equinox, March 21, had moved 11 days away from the astronomical event. Gregory solved that problem by adding some other machinations that mean we really don't have a leap year day every 4 years. Some are skipped. (Read the details in this article at http://www.huffingtonpost.com/dr-joel-hoffman/hanukkah-and-thanskgiving_b_4312207.html)
Rav Schmuel had set the Jewish calendar in the first millennium of the Common Era. But he also used the calculation of 365.25 days per solar year and made various complex additions and subtractions of months to accomplish a calendar that matches the secular Gregorian calendar every 19 years. However, no changes were made to account for those extra 11 minutes. So there is a constant drift of the Hanukkah holidays later and later in the year. Probably at some point there will need to be more adjustments made to make sure that Pesach falls in the spring, but that has not been determined yet. Suffice it to say that all of these complexities have made this year's Thanksgivukkah a very very rare event. In fact if the calendars continue as they are, they will not occur again together for some 70,000 plus years.
This confluence of holidays has led to a lot of laughter: Thanksgivukkah, the menurkey ( a turkey shaped menorah pictured above), Gobble tov (the good luck wishes that correspond to Mazel tov in Hebrew), and others. Many Jewish families concocted new recipes for the occasion: cranberry sauce on potato latkes, sweet potato latkes with the turkey, turkey pastrami sandwiches, and others. Hanukkah gelt was used as place cards on the Thanksgiving dinner table. But many Jews wondered how to seriously deal with both holidays. They do have similar ideals: peace, restoration of normal religious life, the joining of multiple cultures, and family celebrations. But some worried that if the two holidays were melded too much each would be diminished by the other. And how many characteristic food items can you eat in a single day? Of course, the best part of Hanukkah is that it continues for 8 nights, so the next and the next day etc, it is still Hanukkah and families could do the special things for Hanukkah on those nights.
My Christian family all gathers at my sister's home for Thanksgiving every year. Our big meal is at noon time. My Jewish husband is Israeli; in his homeland the Hanukkah holiday was never a big holiday. In Israel, Passover and the High Holidays-- Yom Kippur (the day of atonement) and Rosh Hashanah (the Jewish New Year) -- are the major holidays. Even Purim and Succoth are more prominently celebrated than Hanukkah. So this year's combination was not a problem for my husband. It was me that decided I wanted to honor the Hanukkah holiday in some way. So I took a menorah and the candles, some Hanukkah gelt, and a dreidl along with me to my sister's home. I asked my son to tell me about 45 minutes before they were going to leave so that I could light the menorah for my grandsons. I told them the Hanukkah story and we played some dreidl games. The day had been stuffed with sweets, so I secretly handed the gelt to the parents of the children and told them to present it later. Other more distant relatives in the family asked questions about Hanukkah and commented about it. My sister usually puts out some leftovers and some snacks, cheese and crackers, etc late in the afternoon for those that might be getting hungry. I had brought along some latke mix and I made latkes and served them with sour cream and applesauce. I felt there was enough of the Hanukkah holiday to make an impression on my grandchildren and it did not interfere in any way with my sister's celebration of Thanksgiving.
I stayed overnight with my mother and then the next day drove back to Milwaukee. I always call my 96 year old mother when I get home so she knows I am back safely. This time when I called her, she told me: "I forgot to say anything to you about this last night, but I thought it was wonderful what you did about Hanukkah. I saw the little boys taking it all in, and even some of the adults were asking questions. I think you made some people think about other traditions and other holidays. I am glad that you did that." Now I have to fill in the back story a little bit here. My parents had a terrible time with my marriage to a Jew, and especially to an Israeli (read foreigner) Jew. I don't want to go into detail, but suffice it to say it was a very difficult time for all of us. But even my mother who had the worst time of it, had grown to know my husband's parents, visited them in Israel with a Jewish tour group of all things, and entertained my Israeli father in law in Arizona for the winter years ago. So she had been made tolerant and accepting a long time ago, but I was still very much intrigued that she had made this statement to me that next day. I once told my husband that I thought marrying him had broadened my life to an extreme degree and he had repeated the same thing to me. I think our union also may have broadened the horizons of other people in my family as well. That can only bring Good!