About a month ago, I saw a short article on the Asahi Shimbun about Diamond Fuji (ダイヤモンド富士). I had never heard of the term Diamond Fuji before. The article had a very pretty accompanying photo of the rising sun—a big orb of deep, radiant yellow and orange glowing in the early morning air—just cresting Mt. Fuji, whose peak was just about symmetrically silhouetted against the sun's disk from the camera's perspective. The photo was taken on the early morning of July 9, 2013. This scene, in which the rising or setting sun aligns with Mt. Fuji's peak, as seen from certain vantage points, is what is referred to as Diamond Fuji.
At first, I just stared at the photo, wondering what the significance was, and why the Asahi Shimbun, a major Japanese newspaper, was running an article on it. I was puzzled even after reading the Japanese article. Then, after a while thinking about it, I had my duh moment and realized that, from a certain vantage point around Mt. Fuji, which is located around 100 km (62 miles) southwest of Tokyo, such a scene, such a photo, was only possible on certain days of the year, at certain times of those days (around sunrise and sunset), and then again only if the weather allowed.
The photo in the article was taken by a Buddhist priest who was in Kawakami, Nara Prefecture, at an impressive distance of about 277 km (172 miles) southwest of Mt. Fuji, at an elevation of 1350 meters. He took the photo using a camera with a 300mm zoom lens.
Because the Earth revolves around the Sun, and the Earth's axis of rotation is tilted and not perpendicular to the orbital plane, the Sun's apparent path across the sky changes as the year progresses. The position where the Sun rises on the horizon, as observed from a certain location, moves predictably with the day of the year. Similarly, as seen from a certain vantage point around Mt. Fuji, the position where the Sun crosses behind Mt. Fuji on its way up or down marches with each day of the year. Since the Sun rises in the east and sets in the west, Diamond Fuji will occur sometime before sunset if you are located to the east of Mt. Fuji; if you are to the west, Diamond Fuji will occur sometime after sunrise. For these places, the window within which this special sight is visible opens twice a year. To get a glimpse of Diamond Fuji, one must be at the right place at the right time, with luck and the weather gods on one's side.