In Japan, the moment when the sun sits exactly on the summit of Mt. Fuji is called “Diamond Fuji”, and when the full moon does, “Pearl Fuji”. This web app calculates when and from where you can see such alignments — not only with Mt. Fuji, but with skyscrapers and any mountain or building you choose (“Diamond XX” / “Pearl XX”).
It’s free, has no ads, needs no sign-up, and runs in the browser on PCs, phones and tablets. ← Back to the app
What you can do
Set the observer (where you watch from) on the map, from your current location, by latitude/longitude, or with a Google Maps URL. The ground elevation is fetched automatically from GSI (Geospatial Information Authority of Japan) data
Targets include Mt. Fuji and skyscrapers 70 m or taller (including towers) that you can pick on the map. Over 2,300 buildings in Sapporo, Sendai, Saitama, Chiba, Tokyo’s 23 wards, Yokohama, Kawasaki, Nagoya, Kyoto, Osaka, Hiroshima and Fukuoka have simple 3D models (“Skyscraper (simple 3D)”), and about 80 in major cities across Japan have detailed 3D models (“Skyscraper (detailed 3D)”; see the list below). You can also enter any position and height to use a mountain or building as the target. We plan to keep adding skyscrapers
Lists candidate dates and times from today up to 400 days ahead, with the offset from the best alignment (the bottom edge of the sun / moon resting on the top)
Shows the selected Mt. Fuji or building in 3D, which you can rotate with your finger or mouse (simple-3D skyscrapers are their footprint extruded to roof height — so-called 2.5D; detailed-3D skyscrapers use 3D city models down to roofs and spires; Mt. Fuji is an approximate model)
Combines the “Result view” and a map of the observer and target into one image that you can share on social media (with your phone’s share feature, or by saving the image and copying the text)
Check the view on a candidate day in the “Result view”. Drag the sun / moon along its path to see the date and time to the second (handy for finding when they start to overlap)
Bookmark the observers and targets you use often, with names
Observers and targets are limited to Japan (because the app uses GSI’s elevation API and GSI Tiles for the map).
Skyscrapers with detailed 3D models (80)
Sapporo (7)
JR Tower (height 174 m)
Sapporo TV Tower (height 144 m)
D'Grafort Sapporo Station Tower (height 143 m)
The Sapporo Tower Kotoni (height 136 m)
City Tower Sapporo Odori (height 136 m)
Premist Kotoni Sky Cross Tower (height 135 m)
Sapporo Sosei Square (height 132 m)
Sendai (3)
Sendai Trust Tower (height 180 m)
AER (height 145 m)
SS30 (height 137 m)
Tokyo (23 wards) (42)
Tokyo Skytree (Sumida, height 633 m)
Tokyo Tower (Minato, height 332 m)
Azabudai Hills Mori JP Tower (Minato, height 330 m)
Toranomon Hills Mori Tower (Minato, height 256 m)
Roppongi Hills Mori Tower (Minato, height 248 m)
Tokyo Midtown Tower (Minato, height 246 m)
Tokyo Metropolitan Government Building No. 1, North Tower (Shinjuku, height 243 m)
Tokyo Opera City (Shibuya, height 241 m)
NTT Docomo Yoyogi Building (Shibuya, height 241 m)
Sunshine 60 (Toshima, height 238 m)
Tokyo Midtown Yaesu (Chuo, height 237 m)
Tokyo Metropolitan Government Building No. 1, South Tower (Shinjuku, height 236 m)
Shibuya Scramble Square (Shibuya, height 229 m)
Shinjuku Nomura Building (Shinjuku, height 219 m)
Shinjuku Center Building (Shinjuku, height 216 m)
Shiodome City Center (Minato, height 216 m)
Shinjuku Park Tower (Shinjuku, height 215 m)
Tokyu Kabukicho Tower (Shinjuku, height 215 m)
St. Luke's Garden Tower (Chuo, height 212 m)
Mode Gakuen Cocoon Tower (Shinjuku, height 211 m)
Dentsu Headquarters Building (Minato, height 211 m)
Tokyo Portcity Takeshiba Office Tower (Minato, height 209 m)
GranTokyo North Tower (Chiyoda, height 205 m)
Shinjuku Sumitomo Building (Shinjuku, height 205 m)
Shinjuku Mitsui Building (Shinjuku, height 204 m)
GranTokyo South Tower (Chiyoda, height 204 m)
Sompo Japan Headquarters Building (Shinjuku, height 202 m)
Sanno Park Tower (Chiyoda, height 199 m)
Shin-Marunouchi Building (Chiyoda, height 197 m)
Otemachi Tower (Chiyoda, height 197 m)
Izumi Garden Tower (Minato, height 196 m)
Akasaka Intercity AIR (Minato, height 195 m)
Nihonbashi Mitsui Tower (Chuo, height 193 m)
Nippon Television Tower (Minato, height 191 m)
Tokyo Midtown Hibiya (Chiyoda, height 189 m)
Atago Green Hills MORI Tower (Minato, height 188 m)
Capital Gate Place The Tower (Chuo, height 187 m)
Cerulean Tower Tokyu Hotel (Shibuya, height 186 m)
Shibuya Hikarie (Shibuya, height 184 m)
Marunouchi Building (Chiyoda, height 179 m)
Yebisu Garden Place Tower (Shibuya, height 169 m)
Tokyo Metropolitan Government Building No. 2 (Shinjuku, height 157 m)
Yokohama (7)
Yokohama Landmark Tower (height 295 m)
The Tower Yokohama Kitanaka (height 212 m)
Queen's Tower A (height 176 m)
InterContinental Yokohama Grand (height 140 m)
Queen's Tower B (height 138 m)
Queen's Tower C (height 110 m)
Yokohama Marine Tower (height 102 m)
Nagoya (12)
Midland Square (height 247 m)
JR Central Towers (Office Tower) (height 245 m)
JR Central Towers (Hotel Tower) (height 225 m)
JR Gate Tower (height 214 m)
JP Tower Nagoya (height 196 m)
Nagoya Lucent Tower (height 180 m)
Nagoya TV Tower (height 178 m)
Dai Nagoya Building (height 174 m)
Global Gate (height 168 m)
Mode Gakuen Spiral Towers (height 168 m)
NTT Docomo Nagoya Building (height 164 m)
Grand Maison Misonoza Tower (height 151 m)
Kyoto (1)
Kyoto Tower (height 130 m)
Osaka (6)
Nakanoshima Festival Tower (height 199 m)
Kanden Building (height 195 m)
Herbis Osaka Office Tower (height 189 m)
Osaka Umeda Twin Towers North (height 186 m)
Grand Green Osaka (height 182 m)
Umeda Sky Building (height 173 m)
Hiroshima (2)
City Tower Hiroshima (height 196 m)
Grand Cross Tower Hiroshima (height 168 m)
How to use
Simple mode: We recommend starting with “Simple” mode, which shows only the most-used features. Press “Start the easy calculation” and answer a few questions to choose the observer and target and calculate (observers and targets picked on the map can be bookmarked). You can also choose ① the observer from bookmarks, and ② the target from Mt. Fuji, bookmarks or skyscrapers (detailed 3D). It calculates with a 400-day search period and an allowed offset of ±2.0. To enter latitude/longitude or fine-tune values, switch to “Detailed” mode at the top of the page
① Observer: In detailed mode, click the map or drag the (blue) pin to set the observer position. If you watch from a building, enter the “Observer height above ground”
② Target: Choose Mt. Fuji or another target. For other buildings, use the “Pick on the map” map: click a skyscraper marker, or place the (red) pin anywhere and enter the height
③ Conditions: Choose the sun (Diamond) or the moon (Pearl) and press “Calculate”
Candidates: Tap a row to show that day in the “Result view”. Tap ▶ to expand five days including the two days before and after (sun only). ★ marks the candidate with the smallest offset
Offset: How far the sun / moon is above or below the best alignment (its bottom edge resting on the target’s reference point — the center of the summit disc for Mt. Fuji, the top for buildings), with the apparent size (diameter) of the sun / moon as 1 (+ is above, − is below, 0 is best). Candidates beyond the “Allowed offset” are not shown
Result view: Drag to look around, scroll / pinch to zoom. Drag the sun / moon to move it along that day’s path (dots every minute); the date and time (to the second) are shown at the top left (if “Let the sun move to other days” at the bottom right is on, the sun can also jump to the paths of the days before and after). The distance ring is the distance from the observer, green is the target, and the yellow / white arc is the path of the sun / moon
Using the map and result view on a phone: To keep page scrolling smooth, the map and result view are locked. Double-tap, or use the padlock button at the bottom left, to unlock them (you can also use the map in full screen). While locked, tapping the map doesn’t move the pin. Double-tap again while unlocked to lock. Touching outside the map / result view locks it again
Language: The app follows your browser’s language. You can change it in Menu → Settings → “Language”
Install as an app
Add it to your home screen to use it like an app (still free, no sign-up).
iPhone / iPad: Open in Safari, tap the Share button → “Add to Home Screen”
Android: Open in Chrome, tap the menu at the top right → “Add to Home screen” or “Install app”
PC: Open in Chrome or Edge and use the install button at the right of the address bar, or “Install” in the menu
Once installed, it uses the whole screen without the browser frame and opens straight from your home screen. The pages and the calculation part you have opened are stored on your device, so even with a weak signal you can calculate from bookmarks and history and use the result view (the map, elevation lookup and skyscraper display need the internet). When a new version is available, the app asks whether to update.
How it calculates, and caveats
The positions of the sun and moon are calculated with published astronomical formulas (for the moon, those of Meeus, “Astronomical Algorithms”). Compared with NASA JPL’s ephemerides (JPL Horizons), the error is 0.005° or less for both (about 1/100 of their apparent size)
The target is treated as “a single point at the top” (for Mt. Fuji, the center near the summit crater; for buildings, the top). Building width is not used in the calculation
The curvature of the earth and the bending of light by the atmosphere near the ground (refraction) are corrected with standard values. Actual temperature and pressure can change the view slightly
Whether mountains or buildings in front block the view, and the weather, are not taken into account. Please check the line of sight and the weather on site before you go
Building heights are as of when the source data was measured. Buildings rebuilt or renovated since may differ
Times are shown in Japan Standard Time (JST)
Disclaimer and safety
The results of this app are estimates. Their accuracy and completeness are not guaranteed.
The developer accepts no liability for any damage arising from the use of this app.
Never look directly at the sun, or at the sun through binoculars, a telescope or a camera viewfinder. It can damage your eyes.
When observing, stay out of restricted or dangerous places and watch out for your surroundings and traffic.
Security and privacy
No ads, ever. No account registration either
All calculations run in your browser. The app talks to external servers only in the following cases, and never sends information that identifies you, such as your name
Elevation lookup: sends the latitude/longitude of the observer and target to GSI’s elevation API
Map display: loads map images for the visible area from GSI (GSI Tiles)
Skyscraper display: loads building data for the visible map area from a database run by the developer (Supabase)
Map search: when you search for a place or building name on the full-screen map, the text you typed is sent to GSI’s place-name search API and to the building database above (Supabase)
Reading Google Maps URLs: short URLs (maps.app.goo.gl) are expanded to the original URL via a server run by the developer. Only the pasted URL is sent
Display components: the components for the map, result view and QR code (Leaflet, Three.js, qrcode) are loaded from public CDNs
Donation button: the image of the donation button at the end of the results and on this page is loaded from the donation service Ko-fi (on this page, the button component and fonts (Google Fonts) are also loaded)
Analytics: To count page views, anonymous statistics (pages viewed, browser type, etc.) are sent to the analytics service GoatCounter. No cookies are used and no information that identifies you is sent
The location from “Use current location” is used only to fill in the observer fields
Share images are created in your browser. Images leave your device only when you share or post them yourself. The map in the image shows the observer position, so be careful if it’s your home
Information stored only in your browser (localStorage) is listed below. It stays on your device and is never sent outside
The last observer and “Pick on the map” target (to restore them next time)
Observer and target bookmarks
Calculation history (the 10 most recent and pinned ones)
The contents of Menu → “Settings” (including the language), and whether you use simple or detailed mode
“Result view” setting (whether the sun may move to other days)
That you agreed to the disclaimer and safety notes
Terms of use
This is a translation of the Japanese terms. If there is any difference, the Japanese version prevails.
Anyone, individual or business, may use this app free of charge
You may use the results, share images and screenshots on social media and blogs, and also for work (researching tours, promoting “rooms with a view of Diamond Fuji”, printing in brochures, ads or websites, etc.)
When you use or publish them for work, please credit the following three items (optional for personal social media and blogs, but appreciated)
App name: Diamond, anywhere (or どこでもダイヤモンド)
Author: itachiwalker
URL: https://diamond.itachiwalker.com/
Do not present anything in a way that suggests the author guarantees or endorses it
The maps in the images are GSI Tiles from GSI. When printing them or using them in ads, please also follow GSI’s terms of use
Prohibited
Selling this app itself (program or screens), or offering it as part of a paid service or product
Downloading this app’s files and publishing or running them anywhere other than this service (diamond.itachiwalker.com)
Copying, modifying or redistributing this app’s program
Analyzing its internal structure by decompiling, disassembling, deobfuscating, etc.
Putting excessive load on this service, such as heavy automated access to the skyscraper database or bulk downloading of its data
Disclaimer
The results are estimates. Depending on terrain and building-height data and the assumptions of the calculation (standard refraction, etc.), the actual date, time and position may differ. If you use them for work, we recommend checking on site
The author accepts no liability for any damage arising from the use of this app (including damage from use for work)
* The 3D city model “PLATEAU”, on which the 3D models and skyscraper data are based, is licensed under CC BY 4.0. The components used for display are listed under “Open-source licenses” below.
Data sources
Map: GSI Tiles (Geospatial Information Authority of Japan)
Elevation: GSI elevation API
Place-name search on the map: GSI place-name search API (place names in Japanese only)
Skyscrapers and building 3D models: some 3D models in this app are created by processing the 3D city model “PLATEAU” maintained by Japan’s Ministry of Land, Infrastructure, Transport and Tourism (CC BY 4.0)
Some skyscraper names: Wikidata (CC0). Buildings without an English name are shown with their Japanese name
Shape of Mt. Fuji (“Result view”): an approximate model based on Chiba, T., “Topography and disaster prevention of Fuji volcano viewed in polar coordinates” (JpGU 2014) and “Topography of Mt. Fuji: an analysis by cylindrical-coordinate transformation of a 50 m DEM” (Fujigaku Kenkyu 7(1), 2010) (titles translated)
FAQ
Q. When I pick a skyscraper (simple 3D) on the map, the pin (the point used for the calculation) is off the center of the tower
A. The position of a skyscraper (simple 3D, red-violet marker) is the center (centroid) of the building’s whole footprint in the source data (PLATEAU). For buildings with a wide podium and a slim tower on top, the pin can be off the tower’s center. The calculation uses this position, so the closer you watch from, the more the resulting times shift.
In that case, zoom in until the building outline is shown, and drag the pin to where the tower’s center seems to be (it can move only inside the outline). The building’s name and height are kept; enter a “width” to calculate.
Skyscrapers with detailed 3D (blue-violet marker) use the top of the tower as the reference, so they don’t have this offset (their pin can’t be moved).
Q. What is the “width” used for?
A. Only for drawing the building in the “Result view”. The calculation (candidate times and offsets) uses a single point at the top of the building, so the width doesn’t affect the results. A rough value is fine.
When you pick a skyscraper (simple or detailed 3D) on the map, it’s drawn from the source data, so no width is needed (the field is disabled). If you move the pin inside the outline, enter a width.
Q. Pressing “Use current location” shows “Couldn’t get your location: User denied Geolocation”
A. Your device or browser settings are blocking location access for this site. The app can’t change this permission, so please check the following settings (item names vary slightly with the iOS version).
iPhone / iPad (Safari):
(1) Settings → Privacy & Security → Location Services is on
(2) Further down on the same screen, set “Safari Websites” to “Ask Next Time Or When I Share” or “While Using the App” (with “Never”, requests are denied without asking)
(3) Settings → Apps → Safari (on iOS 17 and earlier, Settings → Safari) → Location: set to “Ask” or “Allow”
(4) If you chose “Don’t Allow” for this site before, open the menu in Safari’s address bar (the “AA” button, etc.) → Website Settings → Location, and set it to “Ask” or “Allow”
After changing the settings, reload this page and press “Use current location” again.
If you use Chrome or another browser on iPhone, go to Settings → Privacy & Security → Location Services and set that browser app to “While Using the App” or similar.
Even without location access, you can set the observer by clicking the map or with “Enter lat/long or URL”.
Q. Some names are still in Japanese
A. Place names in the map search come from GSI and are in Japanese only. Skyscrapers without an English name in our data are shown with their Japanese name. Names you enter yourself (bookmarks) are shown as you typed them.
Bug reports and requests
Please send bug reports and requests for buildings, areas or features via GitHub Issues (a GitHub account is required). English is welcome.
This app is free and has no ads. It is developed and maintained as a personal hobby, and donations are completely optional. Only if you found it useful or got a beautiful photo with it, support through the button below would be a great encouragement.
Open-source licenses
This app uses the following open-source software.
Leaflet 1.9.4 — BSD 2-Clause License
BSD 2-Clause License
Copyright (c) 2010-2023, Volodymyr Agafonkin
Copyright (c) 2010-2011, CloudMade
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Copyright (c) 2012 Ryan Day
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
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