“On this day long ago, a child was born who, by age 30, would transform the world. Happy Birthday Isaac Newton b. Dec 25, 1642.”

Astrophysicist Neil deGrasse Tyson tweeted that factoid on Christmas Day, which also happens to be Newton’s birthday (depending on which calendar you use, but we’ll get to that later). Some people weren’t happy about it, accusing Tyson of a Dickensian dismissal of Christmas spirit.

The backlash was enough to prompt Tyson to weigh in on the ordeal the following night.

His tweet was followed by a lengthy Facebook post. “Well. It’s official. Far and away my most re-tweeted tweet appeared Christmas day,” he began, adding:

My sense in this case is that the high rate of re-tweeting, is not to share my enthusiasm of this fact, but is driven by accusations that the tweet is somehow anti-Christian. If a person actually wanted to express anti-Christian sentiment, my guess is that alerting people of Isaac Newton’s birthday would appear nowhere on the list.

As of Monday morning, the tweet in question had surpassed 77,000 retweets.

Tyson’s explanation appeared after a mini-argument on Twitter grew into a full-blown, slow-news-cycle controversy. The New York Post said the scientist’s Christmas observation “angers Christians,” and a parody Twitter account for a fake conservative U.S. representative tweeted some (presumably fake) outrage at Tyson:

As Tyson’s Newton tweet gained steam, he tweeted a few other observations that also became controversial, such as this one:

But his other tweets didn’t come close to taking off like his observance of Newton’s birthday did.

“War on Christmas?” the Christian Science Monitor wondered in a headline.

So what is it about the Newton tweet that garnered so much controversy? It can’t be Newton himself — the man was religious, and wrote extensively on theology and the Bible, even if his theology was, perhaps, not strictly orthodox for his time or ours.

And it can’t simply be that Tyson noted the fact that Newton was born on Christmas Day, because Tyson published a nearly identical tweet last year on Christmas, and it didn’t garner nearly as much attention:

Tyson himself wrote on Facebook that the volume of retweets was shocking: “I wonder if you are as astonished by this fact as I am. For example, I’ve made direct reference to Jesus in previous tweets that have not come close to this number. How about:

“‘Some claim the USA is a Christian nation, compelling me to wonder which assault rifle Jesus would choose: the AR-15 or AK-47.'”

It seems likely that the controversy has a lot to do with the astrophysicist himself. Tyson, the director of the Hayden Planetarium in New York, has long been controversial among religious conservatives for his advocacy of scientific explanations for the evolution of life and the beginning of the universe.

And his profile rose this year, as did his pool of critics, when he hosted the reboot of Carl Sagan’s “Cosmos” — a show that did not shy away from discussing evolution, the origins of the universe and climate change, or from confronting those who believe the scientific consensus is wrong on those issues.

In September, the Federalist published a multi-part series on the accuracy of an anecdote Tyson often tells on the lecture circuit about George W. Bush; Tyson eventually admitted that his contextual explanation for the anecdote was off.

Some of the controversy could have to do with the accuracy of the birthday statement, too. Tyson even addressed it in his post. You see, when Isaac Newton was born, Britain was on the Julian calendar. Under that calendar, Newton was born on Christmas.

“All of England was celebrating Christmas the day Newton was born,” Tyson noted. But not much of Europe was, because the Julian calendar is 10 days longer than the Gregorian Calendar, which was adapted in Britain after Newton’s lifetime but introduced to the Catholic world — i.e. the European continent — in 1584. On the Gregorian calendar, Newton’s birthday is Jan. 4.

Then again, there’s little scriptural evidence suggesting a time of year for the birth of Jesus Christ, either. Christian tradition, not a historical record of Jesus’s life, dictates that it be celebrated in December.

“A humble thanks for your continued interest in what I have to say about life, the universe, and everything,” Tyson wrote on Facebook. “But most importantly, enjoy a Happy New Year.”

In the new year, he added, “I’ll be tweeting about Earth’s perihelion. Just a head’s up in case people want to avert their eyes over that one.”