Kanayama Calendar and Astronomical Cross-Quarter Dates




The Kanayama solar calendar features solar observations made on certain dates of the year. These are dates that we, at Kanayama Megaliths, refer to in Japanese as yontobunand in American English as half-angle dates.

The astronomical cross-quarter dates are those days of the year when the sun’s declination angle is midway between its summer solstice or winter solstice declination and the zero angle at equinox time. Notice that the dates come in pairs. The winter pair occur when the declination is half of the approximately -23.5 degrees. The summer pair occur when the declination is half of +23.5 degrees. These dates are fixed all around the planet, independent of latitude or longitude.

The astronomical cross-quarter dates given by Universe Today (see link below)


are 10/24, 2/18, 4/21, 8/22 for 2015. They agree to within one day or two with Kanayama.

We, at Kanayama Megaliths, have hesitated to use the term “astronomical cross-quarter dates”(although it is correct) because, in Europe and in America, people think it means the pagan holidays called “cross-quarter holidays” such as Lammas and Halloween which fall approximately mid-way (about 45 days) after the solstices and the equinoxes.


If you have been following our posts, you know that the Kanayama half-angle dates occur in pairs. The winter pair  are about 60 days before and after the winter solstice. The summer pair are about 60 days before and after the summer solstice. For reference we list them here.

Winter:  10/23 and 2/19.     Summer:  4/22 and 8/20

The Kanayama Megalithic Solar Calendar makes full use of these two pairs of dates. On those days of the year, special observations of sunlight are made. They help to pinpoint the exact dates of summer solstice and winter solstice, which is what a calendar is meant to do. This is, to a large extent, why the Kanayama Calendar is so accurate.


The summer and winter observations




One thought on “Kanayama Calendar and Astronomical Cross-Quarter Dates

  1. Pingback: Iwaya-Iwakage Spotlight, April 2017 | Iwaya-Iwakage of Kanayama Megaliths

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