The maximum number is five. Each calendar year MUST contain a minimum of two lunar eclipses. (It must also have a minimum of two eclipses of the sun.) There can be as many as five eclipses of the moon. The next year with five lunar eclipses will be 2132.

Here’s how it works. Eclipses do not simply happen at random. They only take place at certain times of the year, during what are called “eclipse seasons.” Each eclipse season is as much as 37 days long. If a full moon happens during those 37 days, there will be a lunar eclipse. If there’s a new moon, we’ll have an eclipse of the sun.

Full moons and new moons take place about 14 to 15 days apart, so there must be at least one of each in every eclipse season. One lunar eclipse. One solar eclipse.

If a full moon happens shortly after the beginning of a 37-day eclipse season, there will be enough time for a second full moon before the season ends. That means you will have two lunar eclipses in one eclipse season.

Eclipse seasons fall about 25 weeks apart. That means that there must be at least two in each year. There must be at least one lunar eclipse in each. It can also happen that in BOTH of the eclipse seasons, full moons happen near the start and near the end, making as many as four lunar eclipses.

Since eclipse seasons are 25 weeks apart, it is possible that one might start in early January, the second in late June/early July and a third in late December. If there happened to be two lunar eclipses in the January season and two in the June season, and if the December full moon also comes before New Year, you could get five lunar eclipses in a single year. The last time it occurred was 1879. The next time will be 2132.

Six lunar eclipses, by the way, are impossible in a single calendar year. If the December eclipse season started with a full moon in late December, the next full moon could not take place until January, beyond the end of the year.

Eclipse seasons migrate through our calendar. In 2007, the eclipse seasons took place in March and in late August/early September. The next one will be February 2008, and there will be a total eclipse of the moon visible the evening of February 20th. (In Europe, it falls on February 21st.)

1. Penumbral Lunar Eclipse

the moon passes through Earths penumbral shadow.

2. Partial Lunar Eclipse

A portion of the moon passes through the earth’s umbral shadow.

3. Total Lunar Eclipse

The entire moon passes through Earth’s umbral shadow.