Wondering what primary astronomical cycles there are that are greater than a year (which is a cycle around the sun), but less than 1000 years-ish (on that scale). There is the cycle of the moon phases too, and the cycle of the earth making a full rotation (a day). But I wonder if there are any cycles at a bigger-than-a-year scale, but not too big. I guess there's also the cycle of a stars life (but that is kind of a big scale, on the order of billions of years), but I am more wondering in terms of rotation what sort of cycles there are. I guess there is another one, Axial Precession, but that is a bit large such as on the order of tens of thousands of years. Maybe there are some cycles of the planets in which they are visible from earth, or of their moons, or of comets, or of nearby stars or that kind of thing.

If there were ones around each of these points that would be nice: 2, 5, 10, 20, 50, 100, 500, or 1000 years sort of thing.

Basically I am looking for "interesting" or "popular" cycles rather than just picking any of them (since every planet and moon has an orbital period). I am looking for ones that (a) we can observe most easily either directly without a telescope, or with a simple telescope/binoculars, and/or (b) have significance of some kind historically perhaps. If there is one that is historically significant or historically popular (say something Newton or Kepler talked about for example) but is difficult to see, that would be okay too.

For example, I vaguely remember hearing people mention "hey these x and y planets just aligned, it only happens every x years", so did a quick search and found this saying Jupiter and Mars align every 2-3 years. That is pretty interesting, since it is a small timeframe, bigger than a year, and you can see it pretty easily. I would like to find a few others though, spread over the scale (as mentioned above) from 1-1000 years. Here is another interesting one, a "Super Blood Blue Moon" as NASA is calling it, which hasn't happened since 1866 (so let's say ~150 years). Not sure if that will cycle every 150 years like that, but something that does cycle similar to this is also exactly the sort of "cycle" I am looking for.

  • 2
    $\begingroup$ Hi. It might help to know why you ask. All of the planets farther from the Sun have an orbital period (their "year", see sidereal period on en.wikipedia.org/wiki/Orbital_period) which is longer than 1 Earth year. Does something like that suit your needs? The planets also have a synodic period (when the planet appears to return to the same position relative to the Sun) which are around 1 to a few years. $\endgroup$
    – JohnHoltz
    Nov 21 '18 at 4:48
  • $\begingroup$ That is good to know. I've updated the question with some details. Thank you. $\endgroup$ Nov 21 '18 at 7:00
  • 3
    $\begingroup$ You could check out eclipse cycles, one of the most famous being the Saros cycle, an 18-year cycle (more precicely 6585.32 days) that was known to Babylonians more than 2,000 years ago. $\endgroup$
    – FSimardGIS
    Nov 22 '18 at 1:50
  • 2
    $\begingroup$ Also see the Metonic cycle of almost exactly 19 years, and various related cycles. $\endgroup$
    – PM 2Ring
    Nov 22 '18 at 12:56

The Moon does not follow the ecliptic precisely like the Sun does; rather, it follows a path inclined of about 5.14°. The two points where the ecliptic and the Moon's path coincide are called 'nodes', and they travel around the ecliptic in a period of 18.66 years. This is a combination of the orbital period of the Moon, also called the sidereal month, about 27.32 days, and the slightly shorter draconic month, the average period between the moment where the Moon traverses a node, which is 27.21 days.

Once every 18.66 years, the ascending node coincides with the vernal equinox, and the Moon will reach declinations of about +28° and -28° (much more than the Sun, which reaches ±23°); this is called a 'major lunar standstill'. 9.33 years later, the opposite is true, and the Moon will only reach ±18° during a 'minor lunar standstill'.

According to Wikipedia these moments have had historical significance, all the way back to the Bronze Age:

This time appears to have had special significance for the Bronze Age societies, who built the megalithic monuments in Britain and Ireland. It also has significance for some neopagan religions. Evidence also exists that alignments to the moonrise or moonset on the days of lunar standstills can be found in ancient sites of other ancient cultures, such as at Chimney Rock in Colorado and Hopewell Sites in Ohio.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.