On NPR’s Morning Edition yesterday, they had a brief item about the leap year, reported by Renee Montagne:
We woke up this morning to the rarest of dates: February 29th, the odd extra day that comes every four years, since there are, apparently, more than 365 days in a year.
A few sentences later, she noted this:
So, every four years we get a leap day. Making some sort of adjustment is key, otherwise the calendar would slowly become out of synch with the seasons.
But then she added something strange:
The Hebrew calendar adds a whole extra month, every 19 years.
Um, no. That’s not right.
The Hebrew calendar adds an extra month, Adar I, but it has nothing to do with the extra quarter day: it’s to reconcile the lunar calendar with the solar one, and that shift is not slow. And the extra month is not inserted once every 19 years, but seven times every 19 years.
This stuff isn’t hard to get right... it just takes a little checking, and whoever wrote that NPR item just tossed it out there with no checking at all.
They must have gotten it with both barrels, and quickly. By the time I went online to check the audio, they had corrected the online version without a word about the error. The line about the Hebrew calendar was removed, and replaced by a bit of silliness:
Not quite Christmas in July, but it might feel that way.
I like the way the New York Times makes its online corrections: they leave the error there, and tell you what the correction is. Too bad NPR doesn’t do the same.
 Yes, it’s odd, but the added month is considered Adar I, while Adar II is the normal one (just called Adar in the 12-in-19 off years).
 This keeps, for example, Passover in the spring. The date moves around from year to year, but only within a few-week period. In contrast, the Muslim calendar, which is also lunar, does not have any correction. That means that there’s no resynch with the solar calendar, and Ramadan, for example, wanders throughout the year. Muslim friends tell me that the daytime fasting during Ramadan is much harder when it’s in June or July than when it’s in December or January.