The moon disc meditation, in Japanese Gachirinkan 月輪観, is one of the basic contemplations of esoteric Buddhism in Japan. It begins with a single image, the full moon. What's meant isn't so much the moon in the sky or the romantic moon of the poets, but a bright, flawless circle of light that reflects the mind itself. In Shingon this moon stands for something everyone carries within, the pure original mind, which is often hidden under the layers of everyday life, thoughts and habits.
What is Gachirinkan? 月輪観
Gachirinkan belongs to the esoteric Buddhism that Kūkai (Kōbō Daishi) brought from China to Japan in 806. It's still practiced in Shingon temples today, and it's closely connected with what Shingon calls bodaishin 菩提心, the mind of awakening.
An important textual source is the Bodaishinron 菩提心論, "Treatise on the Mind of Awakening," which Kūkai valued very highly. It compares the mind of the practitioner to a full moon. In other words, the moon in this contemplation isn't a symbol for something else. It shows the pure mind itself, and the practice uncovers what is already there.
The moon behind the clouds 空海
For Kūkai, the question wasn't whether people have Buddha-nature, but why they don't see it. You could put his answer like this: because the mind is veiled, like the full moon behind clouds. Gachirinkan is a practice in which the clouds slowly become transparent, through inner seeing (kan 観) rather than through effort or thinking.
The moon as a spiritual image is much older than Shingon, of course. It also plays a role in shamanic Daoism, in mountain asceticism and in Shintō, where the full moon stands for purity, clarity and the ability to see in the dark. As a young man, Kūkai himself practiced in the mountains. I think it's very likely that these older layers resonate in the moon contemplation too.
What the moon stands for 月
In Shingon, the full moon stands above all for purity, fullness and quiet radiance. The moon disc is flawlessly white, without stains or shadows, and this is the nature of the pure mind, the original awakening (hongaku 本覚) present in every being. It's a full moon and not a crescent, because the mind of awakening isn't something you have to earn. It's already fully there, and the practice doesn't add anything but removes what veils it. And the moon doesn't burn like the sun but shines quietly, a bit like an insight that doesn't come from the intellect but from a deeper layer.
There's also a close connection with the Siddham syllable A. In the Ajikan meditation, the Siddham A (Bonji in Japanese) appears on a moon disc above a lotus. In Shingon, A stands for the "originally unborn," the origin of all things. Moon disc and A together form a complete image, the clear mind in which universal wisdom dwells.
Gachirinkan isn't a visualization in the sense of "imagine something pretty." It's a contemplation with a clear inner structure, which is passed on personally in the initiation. My chapters in the German Das große Buch der Reiki-Symbole contain moon meditations, but here on the blog I'm only describing the background.
Gachirinkan today 今
In Shingon temples Gachirinkan is still practiced today, as part of the monks' daily practice, as preparation for more complex rituals and as a meditation of its own. In my Kuji Kiri 1, it's one of the foundation practices, together with the breath meditation Sûsokukan and Ajikan, and in Kuji Kiri 9 the three come back together. In Shingon Reiki, too, the moon disc contemplation has a special place.
Gachirinkan doesn't stand alone. It's embedded in breath meditation, Siddham contemplation and mantra practice, and together they form what Shingon calls the path to awakening in this very body, sokushin jōbutsu 即身成仏. Have you ever looked at the full moon and had the feeling that it was reflecting something in you?
Experience the practice
The moon disc meditation is passed on personally in the initiation. If you like, have a look at which entry fits you.
Your Path in Shingon Reiki The Siddham Letters