4. Wasan related to Practical Science and Surveying

Paper Mechanisms

The appendix of Hiden chiiki zuho daizensho include paper mechanism with which we can confirm the positional relations between the sun and the moon.

We find some sheets of paper one on top of another, with a red circle on the top paper indicating the sun. We are supposed to match the red circle with a date on the second paper. Since the second date paper has one hole, we look through the hole to select the right shape from a series of shapes of the moon that are hidden on the third paper. (As the Edo Period used a lunisolar calendar which takes a cycle of the waxing and waning of the moon as one month, we can easily know the shape of the moon from the date such as the moon on the 3rd night (crescent moon) and the full moon on the 15th night.)

This way, we can decide the positional relations between the sun and the moon, and consequently, by turning them as they are, we can approximately confirm in which direction and at what time the moon can be seen.

The new moon on the first day. Because it is in the same direction as the sun, we cannot see it even though it is in the sky during the day.

The crescent moon (moon on the 3rd night). When the sun sets in the west, the moon can be seen in the western heavens.

The full moon on the 15th night. It is exactly opposite to the sun, and it rises from the east in the evening.

The waning moon on about the 23rd night. With this shape of the moon, the left half shines. It rises from the east in the middle of night.