Autumn Equinox at Iwaya-Iwakage 2025

09:04 am. Spotlight on Measuring Stone a

Autumn equinox arrived at the Iwaya-Iwakage on September 23, 2025, but it was cloudy and we have no photos of the spotlight. Ms Chika has provided us with this sequence of photos taken on September 24. As the sun moves from east to west in the morning sky, the spotlight entering from the top of the man-made cavern moves from west to east on the ground. The photo below shows Ms Shiho Tokuda placing Template Stone tool B on the measuring stone. It shows that the stone tool has the same size and shape as the spotlight.

09:13 am. Shiho Tokuda placing Template Stone B

09:21 am. Spotlight shines on Template Stone with the same shape.

09:27 am. Spotlight is nearing the edge of Measuring Stone a.

09:42 am. Spotlight moving to the east

11:00 am. Spotlight even further east

An incense stick is lit so that the sunbeam striking the particles of smoke show us the path of the light. Note how the shape of the spotlight has changed over the course of its journey across the measuring stone and the floor of the cavern.

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July 21, 2025 Dashed line

The dashed line on July 21, 2025 13:12, thirty days after the summer solstice

The dashed line of the Senkoku grouping appeared as expected thirty days after the summer solstice. It indicates that the late summer season will end in another thirty days.

We thank Ms. Chika for sharing her photo with us.

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April 21, 2025 Early Summer: The “Sun Dagger” Inside the Senkoku Grotto

There is a panel on the stone “wall” of the Senkoku Grotto. A beautiful wedge of light appears from sixty days before the summer solstice to sixty days after. The appearance of the light on April 21 indicates the start of the early summer season, and the summer solstice on June 21 is the start of the late summer season.

Ms. Chika was there on April 21 and took a series of six photos at times 07:36, 07:45, 07:52, 07:58, 8:00, and 8:03. We show them below. The wedge of light reminds us of the “sun dagger” on the spiral inside the cave of Chaco Canyon in New Mexico.

The wedge of light shines on the center of the slab on April 21. Each day after, the light moves to the left until the left-most edge of the slab is reached on summer solstice. Then, the light moves toward the right, mirroring its movement until it ends on August 20.

Kanayama Sun Dagger April 21, 2025, 07:36 to 08:03. Photos by Ms. Chika

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April 21, 2025 Early Summer Begins at the Senkoku Grouping

The grotto of A stone is in the shadow of C stone on April 21 07:29. The grotto will be fully illuminated on 6/21, the summer solstice. All photos by Ms. Chika.

The observations made on April 21 relate to the first day of the early summer season of the Kanayama Solar Calendar. It announces that the summer solstice will follow in sixty days. Three types of observations are made at the Senkoku grouping, namely at A and C stones. Ms. Chika was there and took these photos to share with us.

Another observation at the Senkoku grouping is made when one sits at the special observation “seat” near the south end of stone A. Then, you will see the sun appear at the top of stone C. The photo below was taken at 8:37am.

The sun appears over the three-quarters point of the C stone on April 21 08:37, when viewed from the observation point outside of A stone. On the spring equinox it showed at the top right. The sun rises further north (the left of photo) until the extreme point at the center of C stone on the summer solstice of June 21.

There is third spectacular sight inside the upper grotto of A stone, which we will post next. In addition, observations for April 21 can be made inside Iwaya-Iwakage, but we are not reporting them this year.

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March Equinox 2025 at Iwaya-Iwakage

Sequence of photos of spotlight moving toward the template stone on 3/21/2025. The times from top to bottom are 9:37, 9:38, and 9:38+. Photo credit Ms. Chika.

Spring has arrived at the Kanayama Megaliths. These three photos were taken inside the man-made cave of the Iwaya-Iwakage group of megaliths.

On 3/21/2025, Ms. Chika took the beautiful photo of the sun setting due West as seen from an observation point outside and to the rear of the Iwaya-Iwakage.

Setting sun shines through a small opening, as seen at the rear of Iwaya-Iwakage at 4:53pm on 3/20/2025. Photo by Ms. Chika.

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A Non-leapyear Observation, 2025

The leap-year observation stone in Iwaya-Iwakage. The spotlight is leaving the surface of the stone without having reached the tip. Photo by Ms. Chika, taken on 3/1/2025 at 10:07 am.

The year 2024 was a leap year, with leap day on 2/29/2024. The year 2025 is not a leap year. This is confirmed at the Kanayama Megaliths.

In the Iwaya-Iwakage megalith group, leap-year observations are made at this stone shown above. If the coming year is to be a leap year, then this spotlight will illuminate the tip of this stone on 10/15. This is how the ancient Jōmon people knew on our October 15 date that the following year, a day equivalent to our 2/29 leap day would be added. On 2/28 of the leap-year, the spotlight will again light up the tip, and a day would be added the next day.

If, however, the spotlight failed to illuminate the tip of the stone on 10/15, then the following spring would not have a leap-day. The year would be a normal year. This was the case last year on 10/15/2024, and our year 2025 is not a leap-year. This is confirmed by the above photo taken on 3/1/2025. The spotlight clearly misses the tip of the stone.

We thank Ms. Chika for sharing her photo with us.

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Dashed Lines by Supermoon of November 2024

Dashed lines of light from supermoon, November 16, 2024 around 12:25am. Photo by K. Sugisaka.

The beam of light from the sun shining into Senkoku-Ishi creates an amazing line of dashes on the triangular stone in the months of May and July, as we have previously reported.

The bright full moon when in that same position in the sky can do the same. There was a supermoon on the night of November 16, 2024, in Japan. Intrepid observers, Chika-san, Sugisaka-san, and Suzuki-san, viewed the dashes of the full moon close to midnight. Sugisaka-san’s photos are shown here. We are very grateful to our friends for sharing this special experience.

Scenes like this, of spotlights caused by a bright moon, have never before been published.

Closeup of the five dashes a few seconds later.

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Winter 2024 Begins

The setting sun is seen between two megaliths at 15:44 on October 26, 2024.

In the Iwaya-Iwakage chamber, the spotlight moves eastward to fill the stone board. The above two photos were taken at 12:13 and at 12:41. All photos by Ms. Chika.

Sixty days before the winter solstice, solar observations at the Kanayama Megaliths predict that event. On about October 25, early winter begins according to the Kanayama Solar Calendar.

These illustrations from the Kanayama Megaliths guidebook explain what is going on in the Iwaya-Iwakage during the period sixty days before and after the winter solstice. It is only during this period of winter that the low rays of the sun can enter the cavern.

We thank Ms. Chika for sharing her photos once again.

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Autumn Equinox 2024

Iwaya-Iwakage spotlight morning of the autumn equinox. Photo taken on 24.09.23 at 9:16 am.

The setting sun of the autumn equinox is seen between the megaliths of Iwaya-Iwakage. Photo taken by Kazuo Sugisaka on 24.09.23 at 16:37.

The arrival of the autumn equinox was observed at the Kanayama Megaliths at the Iwaya-Iwakage grouping on the hill. In the morning, Ms. Chika photographed the oval spotlight on the rock on the floor of the chamber as Ms. Shiho Tokuda reached toward the light.

The second photo was taken by Kazuo Sugisaka in the afternoon as the equinox sun was setting. One has to stand in just the right place so as to be aligned with the light in the small gap between large megaliths.

We are grateful to Ms. Chika and Kazuo Sugisaka for sharing their photos with us.

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Kanayama Megaliths Observation Event: 30 Days After the Summer Solstice 2024

Sarkura tree in summer at Kanayama Megaliths. Photo by Shiho Tokuda.

This is a translation of the post from the Kanayama Megaliths. Please see the previous posts on Iwakage about the solar observations 30 days before and after the summer solstice, as well as our post on the zenith sun over Hawaii.

July 20-22, 2024
The solar altitude 30 days after the summer solstice (6/21) is the same as 30 days before the summer solstice. The calendar system of the Kanayama Megaliths is improved by using solar spotlights twice a year. This time, we will observe one of them, the dashed spotlight about 30 days after the summer solstice.

Please compare this year’s spotlight carefully with the observation from July 21-23 last year. The difference between this year and last year is related to the leap year, in which one day is corrected every four years.

 July 20, 13:13. The dotted lights appear one by one from the top, but since it rained just before this, we were unable to observe them. The photo shows the six dots already appearing and disappearing from the bottom. The dotted lines are thick and powerful.

 July 21, 13:09. It can be seen that the dotted lines are narrower than yesterday.

 July 22nd, 13:04.  The sunlight is shining through the gap between the huge rocks.The first dotted line is about to be drawn.

13:05.  The dotted line is thinner than yesterday. It is almost the same as July 23rd last year. This year it will last until the 22nd (the average is until the 22nd). Last year’s October 15th was a leap day on the Kanayama calendar. In other words, 2023 is a leap year on the Kanayama calendar. On July 23rd, before October 15th, due to a slight deviation that has accumulated over four years (1/4 day x 4 years), the dotted line was drawn one day later, until July 23rd. Therefore, the dotted light will not enter on the 23rd this year. (Even if it does enter, there will be one or two dots that do not form a line. I will update this after observing tomorrow.)

Today’s temperature was 35.1 degrees…

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