Although I don't know whether I'll be posting anything between now and Easter, it occurred to me that whatever I do post may be confusing to non-Orthodox. What follows is typically tedious, but it may help clarify things. If you start to get drowsy, just skip to the last paragraph.
To my knowledge, all Christian traditions agree on the basic scheme for
scheduling Easter. According to the Gospels, Jesus rose from the dead on
the first Sunday after Jewish Passover, which always fell in the middle
of the lunar month Nisan, which was always the first month of spring.
In keeping with this, Easter always falls on the first Sunday after the
first full moon after the first day of spring. This system,
incidentally, incorporates the three major features of our calendar--the
spring equinox for the solar year, the full moon for the lunar month,
and Sunday for the seven-day week ordained by God. Where the traditions
differ, however, is in the determination of spring.
According to the system set down at the first Ecumenical Synod of Nicea
(AD 325), the start of spring for purposes of calculating Easter was
fixed at March 21 of the Julian calendar, which at that time was the
universal calendar of the Roman Empire. Up until around this time, the
Jewish month of Nisan was determined by observation, much like Muslim
Ramadan is set to this day. The difference was that the Jewish calendar
adjusted for the solar year by adding a leap month if various indicators
suggested that it was not yet spring. Christianity, however, did not
follow a lunar calendar, so a calculated date for Easter made more
sense. Also, because Christianity ended up preceding Easter with several
weeks of Lent, it was necessary to know when to start the movable cycle long before the first moon of spring could be observed.
The system worked fine until the sixteenth century, when the Latin Pope Gregory XIII approved a reform of the Julian calendar. Scholars had noted that the calendar was growing increasingly out of sync with the astronomical data and would continue to do so as long as the solar year was not precisely 365.25 days long. Instead of every year divisible by four being a leap year, they proposed that century years no longer be leap years, unless they were divisible by 400. This would shorten the calendar by three days every 400 years and align it more closely (but still not precisely) with the actual solar year. To correct the divergence that already existed, they went back to the year 100 and adjusted accordingly. This means that right now the Gregorian calendar lags behind the Julian by 13 days. After 2/28/2100, the difference will increase to 14 days.
The Gregorian calendar was not accepted all at once. The newly Protestant countries of Europe were not keen to accept a papally-decreed reform. The British Empire didn't come around until the eighteenth century, just a few decades before the American Revolution. Eastern Europe was even slower, waiting mostly until the twentieth century to change its civil calendar. By that point, much of Eastern Europe was coming under Communist control, and Christians resisted any meddling with the ecclesiastical calendar. After failure to adopt the full Gregorian reform, a compromise was enacted in some Orthodox churches, called the Revised Julian or New Calendar. It accepts the Gregorian system for the fixed calendar but continues to reckon Easter by the Julian date of March 21. The result is that, with few exceptions, Orthodox churches celebrate Easter and Pentecost according to the Julian calendar, while on fixed holidays like Christmas and Epiphany they are divided between Julian and Gregorian. (Loosely, one can say that Greeks follow the New Calendar while Slavs follow the Old, but this leaves out a lot of important nuances.)
All of which is to say that, in any given year, Orthodox Easter might coincide with Western Easter, or it might come a week or even a month later. (The variance is because shifting March 21 by 13 days may also affect by a couple of extra weeks how long it is until the first full moon.) It seems to be least confusing when they coincide or fall far apart. This year, they are separated by a week, so when you're thinking Easter, we'll be thinking Palm Sunday. But just to keep things interesting, we'll both be ending Lent at the same time. In Eastern reckoning, Lent is counted every day and precedes Holy Week; in the West, Sundays aren't counted and Lent includes Holy Week.