The lunar solar cycle, often referred to as the lunisolar cycle, is approximately 19 years long. This cycle is significant because it helps synchronize the lunar months with the solar year.
Over the span of 19 years, there are 235 lunar months (each lasting about 29.5 days) that align with 19 solar years. Essentially, after 19 years, the phases of the moon will repeat on the same days of the year. This cycle is crucial for various calendars, especially those that are lunisolar, like the Hebrew and the Chinese calendars, as it allows them to align their months with the seasons.
In summary, the lunisolar cycle provides a valuable framework for understanding how lunar months can fit into the solar calendar.