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Yearly Eclipse Cycles

There are a minimum of 2 solar eclipses and 2 lunar eclipses every calendar year, though any eclipse is only visible from a portion of the Earth's surface. It's possible - though very rare - to have as many as 7 eclipses in one calendar year. This, in fact, only happens twice in the 21st century: 2038 and 2094.
In 2008, the year's first solar eclipse falls on February 7 and is followed by the year's first lunar eclipse 2 weeks later on February 21. The year's second pairing of eclipses occurs a bit shy of 6 calendar months later, the solar eclipse falling on August 1 and the lunar eclipse on August 16.

Eclipse Rules for any Calendar Year

No matter the year, you know a few things are bound to happen. First of all, expect at least 2 solar and 2 lunar eclipses. When a solar eclipse takes place, you know a lunar eclipse either precedes or follows this solar eclipse by 2 weeks. (Depending on the year, it's also possible for a lunar eclipse to come both 2 weeks before and after a solar eclipse.) The converse is also true: a solar eclipse always comes before or follows a lunar eclipse by 2 weeks. (Again, depending on the year, it's possible for two solar eclipses to bracket a lunar eclipse.)
Another few things you can bank on: if the New Moon flies by its ascending node during the year's first solar eclipse (as it does on Feb. 7, 2008), you can bet that the lunar eclipse coming within 2 weeks of this solar eclipse will find the Full Moon nearby its descending node (like on February 21, 2008). Then, a little less than 1/2 year later, it'll be exactly the reverse. The New Moon will be sweep by the Moon's descending node at the year's 2nd solar eclipse (August 1, 2008), and the Full Moon will bypass the ascending node on the year's 2nd lunar eclipse (August 16, 2008).

From Year to Year

If you haven't read about the total eclipse on the night of February 20-21, I invite you to read it here. We can make a good guess on which date this (descending node) lunar eclipse happened a year ago in 2007 and will happen in 2009. Eclipses often repeat themselves in 354-day periods, this figure representing the length of the lunar year (12 returns to Full Moon).
Because the lunar year is roughly 11 days shy of the 365-day calendar year, it comes as no surprise that the (descending node) lunar eclipse coming prior to the Feb. 21, 2008 lunar eclipse fell on March 3, 2007. Nor does it come as any surprise that next year's (descending node) lunar eclipse will fall on February 9, 2009. I list the present sequence of (descending node) lunar eclipses in the table below:
Date of EclipseType of Eclipse
March 14, 2006Penumbral
March 3, 2007Total
February 21, 2008Total
February 9, 2009Penumbral

Maps courtesy of Fred Espenak

Even though we might expect the next (descending node) lunar eclipse to happen roughly 11 days earlier in late January, 2010, it actually falls one month and 11 days earlier, on December 31, 2009. So here's another rule to go by: when one eclipse sequence ends after several years of duration, the next series begins about 1 month and 11 days (instead of 11 days) shy of one calendar year, and this new eclipse procession continues 9onward afor another several years.

Explanation

Eclipses can't recur some 11 days sooner every year for more than several years in succession. That's because the descending and ascending nodes drift some 8 to 9 degrees westward relative to the Full and New Moon after one lunar year. For a lunar or solar eclipse to happen, the descending or ascending node has to be around 18 degrees or less of the Full or New Moon. After several years, the node drifts too far west for the eclipse series to be able to continue. Click on the eclipse dates on the table to watch the westward progression of the Moon's node. The ecliptic on these maps represents the Earth's orbital plane.
All these maps are available, courtesy of Fred Espenak's Eclipse Page, a treasure-trove of eclipse information.

copyright 2008 by Bruce McClure

The Saros Eclipse Cycle

The Saros Cycle