I started composing a reply yesterday -- I think I didn't post for fear that others wouldn't be interested -- I was surprised that Passover came so far after Easter....if I understand correctly the distance shall tend to grow farther apart after centuries...but the Orthodox Easter is May 1 this year.
I did find some good websites on the Hebrew Calendar though. If my calculations are correct the average Hebrew month is 29.53059414 days, as opposed to the actual lunar month of 29.53058796 days. That amounts to one day's difference every 162,000 years.
Although it looks that the Hebrew year is 365.2468222 days, as opposed to the Gregorian 365.2425 days, meaning one day's difference every 231 years -- I guess that could be a problem in several centuries.
But I don't mean to spoil anyone's Passover -- Shalom.
The Hebrew month is a lunar month, which means that a 12-month year is shorter than the solar year of 365 days. To compensate for that, every so often the Hebrew calendar will include a "leap month" which is an extra month before Passover.
This year included a "leap month" and therefore Easter coincided with Purim, which occurs a month before Passover.
I don't know how the Easter dates are calculated.
I am quoting from Herman Wouk's book, "This is My God," on the Jewish Calendar:
"The Bible says the Jews left Egypt at midnight by the light of the full moon if the spring equinoz, on the fourteenth night of the month Nisan, about thirty-two hundred years ago. This, then, is the night for observing Pesakh, the Passover.
An immediate timing difficulty arises. The Jewish year, like the Mohammedan, has twelve moon months of twenty-nine or thirty days. The year of the sun, which governs the seasons, is about eleven days longer. A moon calendar drifts backward at a rate of about a month every three years. Mohammedans successively observe Ramadan in winter, fall, summer and spring. But the Mosaic law specifies that Passover is a spring holiday; the freedom feast must come in blossom time. The old Jewish solution of this problem was a leap month every few years, proclaimed by the Sanhedrin. When the dispersion destroyed the nation, and communications between centers of learning in exile began to break down, the rabbis worked out a perpetual calendar on a nineteen-year cyle, with seven leap months so arranged as to keep Passover for ever at the equinox. This calendar has the respect of modern astronomers. In nearly two thousand years Passover has not drifted out of the springtime, and in the foreseeable future it will not."