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The Differences and Similarities of
Solar Eclipse and Lunar Eclipse Families
Most of us perceive Eclipses as being a single spectacular event since we seldom get to experience a solar eclipse in our "neck of the woods." On the other hand, we do vaguely recognize that there are about two lunar eclipses each year, but we may, or may not get to watch them. Yet, the truth of the matter is, solar eclipses and lunar eclipses are repeating events that follow a pattern, are grouped together and occur in a series. Although the event may occur on a specific date, we do not always get to witness the eclipse.
What is an Eclipse?
First off, eclipses can only occur during a New Moon or Full Moon while the Sun, Earth and Moon are in alignment in such as way as the light of the Sun is blocked, totally or partially, either by the Earth or by the Moon. When these alignments occur, the North and South Nodes are also a factor. To keep this article as understandable as possible, lets stick to the basics. I can assure you that even at its most simple level, understanding the patterns of eclipses can be difficult. If you want information with more meat in it, there are plenty of technical jargon-filled articles to be found on the Internet. You can Google search them if you want more details. Additionally, you might want to check out some other Lunar Living Astrology eclipse articles via our sitemap.
While there are a lot of online articles and countless books addressing the subjects eclipse events, saros series and node families, many of the explanations are extremely complex and the examples seem to be scattered across multiple pages. Also, there are some very inaccurate explanations. Don't be afraid to do the extra research if a piece of information does not seem to jive. For example, one article I read states that the solar saros usually lasts about 1300 years while the lunar saros only last 900 years. A different online article explains that some years there are no lunar eclipses. These statements are blatantly wrong but the only way to figure it out is to do the research. The hope with this article is to pull a lot of the fragmented information together into a simplistic explanation for convenience sake. On the bottom of the next page, there will be a list of references and resources that can help add information to this piece.
Saros Cycle - A measurement of time
Each eclipse cycle belongs to a series. These are called saros series. There are solar saros series and there are lunar saros series. Each saros series has it own numbering sequence. A lunar eclipse cannot belong in a solar saros series, and vice versa. Each saros series has a beginning and an ending. (See Table 2[next page].) The example is Solar Saros 136. The basic facts are that this series began June 14, 1360 and the last one will occur July 30, 2622. The series will last 1262 years (approximately 12 centuries). Solar Saros Series 136 will exhibit 72 solar eclipses. Of the 72 eclipses in the series, 44 will be total eclipses. The approximate length of time between each occurrence will be 18 years, 11 days and 8 hours. Solar Saros 136 belongs to Node Family 11 and originated from the calculations of the Moon's South Node.
Any of the originating eclipse series will either start near the Moon's North Node or the Moon's South Node. When you look at Table 1 [next page], you will note that the node family column will have numbers followed by N for North or S for South. While the eclipses in each saros series have a beginning and an ending, the node family sequence is eternally repeating. There are always 19 family groups. As a saros series dies out, another series will begin to take the dying eclipse series' place. The new saros series number will share the same node family number as the dying series. For example Solar 2N in July 2000 is represented by Solar Saros 117 and Solar Saros 155. You see this particular duplication happen again in August 2018. Look through Table 1 [next page] to see how many Node Family duplications you can find.
The 19 Node Family groups
The typical node (aka nodal) family group will have four eclipses; two lunar and two solar, with one each originating from north and south nodes. Eclipse cycle after eclipse cycle, the node family numbers will match up with the saros series numbers even as the series is being replaced. As the saros is replaced, we will experience two lunar or solar eclipses approximately one month apart depending on the nature of the eclipse. For example, in 2000, with Node Family 2, we experienced two solar eclipses a month apart on July 1 and on July 31. Saros Series S117 will be dying out and the replacement will be S155. For approximately six to nine times of eclipse events within the family series, we will experience two eclipses of the same node family number, and there will be five eclipse members in the "node family unit." Using the Node Family 2N solar eclipse with Saros S117 and S155 as an example, there were two solar eclipses one month apart in 1928, 1946, 1964, 1982 and 2000. This will happen three more times in 2018, 2036 and 2054 before S117 is gone, but S155 continues on. As you look down through the list in Table 1, you will begin to see similar "ending/beginning" patterns are occurring for solar and lunar eclipses where ever you see more than 4 node family members in the group. We very seldom see more than five in a family group, however, there are rare occurrences of six in a family group. The last time there were six eclipses in a node family was in 1933 & 1935 for Node Family 7 and Node Family 9. Check that one out in Table 3[next page]. In 1933 there were four lunar eclipses in the year while in 1935, there were four solar eclipses. This gave us a total of 18 solar and lunar eclipses in a three-year time span. While this may seem like a large number of eclipses occurring during that amount of time, the truth is that it is not all that uncommon to have six eclipses occur in 365 days. What would be extremely uncommon is to have eight eclipses (solar and lunar) occur in 365 days. I don't know if this has ever occurred or if it is even truly possible.
Beyond the yearly calendar
The normal number of solar eclipses and lunar eclipses occurring in 365 days is five to six. Table 1 gives us an easy view of calendar dates in relation to family groups. What we typically do is look at the calendar starting January 1 and ending December 31. When we do that, we usually only see about four or five eclipse events per year. However, when we take any specific date of an eclipse event, and look for that date in the next year when an eclipse occurs close to it, but less than 365 days, we start to understand that the patterns of five to six eclipses per year are persistent. Each eclipse event within a saros series is approximately 6,585.3 days which breaks down in to 18 years 11 days and 8 hours. There are approximately 82 active saros series individually occurring over an 18 year period.
Eclipses seemingly have their own calendar system. Regardless of the number of actual eclipses occurring within any family group, the time period from one group to the next will be either 340 days or 354 days. The reason behind the difference of 14 days is the lunation of a Full Moon or New Moon. The average number of days spanning each group's cycle, from beginning to end, will be 347 days. To accommodate for the fact that each new series must begin on a New or Full Moon, the next family will not arrive earlier then 340 after the starting date of the previous family group and not more than 355 days after. Part of this difference is due to the type of eclipse grouping. Some families start with a solar eclipse and end with a solar eclipse, like family 19. Some families start with a lunar eclipse and end with a lunar eclipse, like family 17. But, more commonly, the group will start with a solar and end with a lunar, like families 2, 3 & 6, while others start with a lunar and end with a solar, like families 1, 4 & 5. As node families expand and contract in size, the line-ups will change, but the amount of time of one family starting after the prior family started will stay fairly close to 347 days (give or take a week).
Never in the same place twice - but close
Another interesting observation of the saros series is that it moves "through" the calendar of months twice and always ends near the month that it originally began. Check out Table 2 to see how a single saros series of eclipses moves through each month exhibiting two or three eclipses in each month sequentially during the first half of its cycle, then starting over again, spending an additional two to three days in each month over the entire 12 centuries of its trek. After waiting 18 years before eclipsing again, the eclipse moves an additional 10 to 11 days past its previous engagement/event. What this indicates is that each eclipse (lunar or solar) will move through all 12 zodiac signs with approximately six ecliptic events occurring in each sign.
Hopefully, this explanation, along with the various tables on the next page, brings some clarity to the grouping of the saros cycle, their eclipse families and how these groups intertwine through both the astronomical and astrological concepts.