# Viewing "Diamond Fuji"

Diamond Fuji is a phenomenon in which the (typically) setting sun is positioned directly atop Mt Fuji. Some relatively detailed predictions for viewing times at a nearby park are available here.

I will be traveling to Tokyo in early December, and would like to observe Diamond Fuji to the extent possible (if at all). I can rely somewhat on tourist-friendly websites, but information is sparse and imprecise.

Intuitively, one should be able to compute the time and viewing locations of Diamond Fuji for any day of the year: the summit of Mt Fuji lies on the line connecting the viewer to the sun. What is the best way to work out this sort of calendar/map?

As a non-expert I suspect this question is relevant but I am not certain.

• This is really a question better asked on Photography SE but here's a link to a video by one chap explaining the planning of such a shot. Oct 17, 2017 at 1:22
• Theoretically, this is quite easy: just find the altitude and azimuth of Mount Fuji's summit from a given location, and find if and when the sun is at the same altitude and azimuth. The problems: Earth's ellipticity and refraction, while minor, may have a significant effect. This problem is interesting, so I'll look into it and get back to you.
– user21
Oct 17, 2017 at 3:53
• @StephenG perhaps, but this strikes me more as a question about the relative position of celestial bodies, with the constraint of ensuring a particular point lies on the path of observation. For what it's worth, I don't particularly want a picture, I just want to see it.
– kyle
Oct 17, 2017 at 13:13
• This sort of thing crops up all the time for serious landscape shooters, and there are applications and apps for this to do the hard work for times and dates and locations. And if you're there to see it, why not have a go at photographing it - can't hurt and you might get an really impressive shot (does require a little technique, mind you). Oct 17, 2017 at 15:42
• @StephenG interesting; the video is definitely close, but is backwards. I want to solve something like the inverse problem: instead of, "I am standing at X, what date/time is best?" I want to know, "Given a date, what times/locations is Diamond Fuji visible." My precise location in Tokyo is fungible, but my dates are very limited. (my wife and I have an ongoing debate over document-vs-experience)
– kyle
Oct 17, 2017 at 19:26