Something watched you this week.

Watched shows which satellites passed over any place on Earth in the last 7 days, and the real photos they took. It is free, with no sign-up, and the orbit maths runs in your browser.

www.watched.earth
How it works  ·  Run locally  ·  Self‑hosting

_{Palm Jumeirah, Dubai, on 9 November 2026. Open the same place live.}

What it does

1. Pick a place. Search a city, a landmark or coordinates, use your location, drop a pin on the globe, or start

1. It finds the passes. While the globe flies there, your browser replays the past week of orbits for nearly 400

1. It finds the photos. At the same time it searches the Sentinel-2 and Landsat archives, NASA's weather

1. Replay a pass. The satellite flies its real track while the strip of ground its camera sees (its swath)

1. Share it. Post the link anywhere and it shows a preview card made from the real photo, or from the pass's

_{Left: a pass replay, the photo developing line by line as the satellite recorded it. Right: the landing page, with every active satellite in the catalog around the globe.}

_{The same lookup on a phone, and the preview card for a shared pass.}

What watched means

Every pass gets one of four labels, and only the first means an image exists. The line in italics is the rule behind each one.

| Label | What it means | |:--|:--| | ◆ Watched | A real image of this place exists in a public archive.
A Sentinel-2, Landsat or weather photo, or a Sentinel-1 radar image, was matched to the pass. A VIIRS daily mosaic still unchecked after 2.5 s also counts, if the same satellite has a verified mosaic on a later day. | | ◇ Likely watched | A fixed camera's swath covered this place. No photo of it is published.
Sentinel-2 or Landsat in daylight, or a polar weather satellite, with no photo found. | | □ Could have pointed here | A steerable or private camera was in range. Its operator doesn't say whether it looked.
A commercial camera in daylight, or a radar satellite at any hour (for Sentinel-1, whose images are public: none of this pass shows the place). | | + Passed overhead | Crossed your sky, with no camera known to be recording this place.
The ISS or Tiangong at least 10° above the horizon, or a Sentinel-2 or Landsat pass over open ocean (outside Sentinel-2's acquisition plan). |

The results headline (260 satellites watched Palm Jumeirah) counts every satellite with at least one pass, whatever its label, so watched there is meant broadly; only ◆ passes come with an image. The second line counts the images that were made public (photos, weather mosaics and radar images alike), and starts with "At least" while archives are still answering. Geostationary weather satellites never pass; they sit over the equator all week, so they are listed separately and not counted. The app says watched, never photographed.

Accuracy and limits

• Passes are searched for satellites whose cameras, radars or crews Watched knows about, and the geostationary

• In the photos Watched shows, a pixel is 10 m across at best, bigger than a car, so you can't be seen in them.

• The public orbit data (element sets) is accurate to about a kilometre when it is issued and drifts after that, so

• Archives publish a few hours to a couple of days after capture, so the newest passes may not have a photo yet.
• Sentinel-2 and Landsat photos are toned the same way across the whole frame: a black point, a white point and a

• Sentinel-1 radar images are shown at 20 m, the radar's own resolution, in grey with a faint ice tint: brightness is

• The geostationary weather satellites that watch a place all week are listed with their newest frame where a public

Everything uncertain is labelled as such in the app.

How it works

Built with TypeScript, React 19, three.js through React Three Fiber, zustand and Vite. The pass search (SGP4, the standard model for public orbit data) and photo toning run in your browser, in Web Workers; the backend is three Vercel functions and an optional Supabase database.

Four parts are worth a closer look. docs/ARCHITECTURE.md covers the rest, including photo toning, the cloud check at your spot and the share cards, and docs/DESIGN.md covers the visual system.

A pass search with no gaps

Call θ the angle, at Earth's centre, between the satellite and the place, and θ_field the largest θ at which the place can be in the camera's view. That angle can change no faster than ω_max, the orbit's peak angular rate with a 10% margin for perturbations, plus Earth's rotation. So the coarse search steps by |θ − θ_field| / ω_max, clamped between 5 s and 30 min. Between any two samples the same rate limit gives a lower bound on θ, so every interval where θ could reach θ_field is flagged, and no pass falls between samples. Golden-section search then finds closest approach to ±0.1 s, and bisection finds entry and exit to ±0.5 s.

Against a one-second brute force, 22 adversarial cases (both poles, the antimeridian, Null Island, swaths down to 32 km) show no missed passes; where timing is measured, the worst difference is 0.65 s. A week for all 394 satellites (1,860 passes in the test case) takes 1.3 s on one thread in Node; the browser splits it across up to four Web Workers, two on phones. See src/engine/passes.ts.

About 17,000 satellites on the GPU

The globe draws every active satellite in the catalog (16,894 on 9 November 2026). Their element sets become mean Keplerian elements with SGP4's own J2 and J4 secular rates, and a vertex shader solves Kepler's equation for every object, every frame. Against full SGP4 over ±24 h, the median error in low orbit is about 17 km, one or two pixels at globe scale, though one object in twenty is off by more than 100 km. The pass search always uses full SGP4. The globe itself is Earth-fixed and lit by the sun's true direction, computed to about 0.01°, so the terminator, the ocean glint and the city lights are where they really are. See src/engine/elements.ts.

Archive time is not overpass time

A Sentinel-2 scene's archive timestamp (the datetime in its STAC record, the catalog format these archives share) marks the start of the strip the satellite was recording, which can begin minutes before it reaches a given spot (6 min 53 s in one measured case). A photo matches the pass of the same satellite (same NORAD catalog number) whose closest approach falls between 10 minutes before and 60 minutes after that time, and the app always shows the predicted pass time. See src/engine/match.ts.

A locked-down backend

Vercel serves the static app and three functions: share cards (/api/og), share pages (/s/:id) and the usage-event relay (/api/e). Supabase holds lookups, shares and usage counts. Row-level security is on, every table privilege is revoked, clients can only call a handful of Postgres functions, and an hourly pg_cron job rolls up and prunes the events.

Privacy

The orbit maths runs in your browser. The site counts how it is used; it does not track people.

| Record | What Watched keeps | |:--|:--| | Lookup | A cell about 10 km across (0.1°), and that place's country and town. | | Share | The town-level place name, a point rounded to about 1 km (0.01°), the pass and its photos, and a view count. | | Visit | What happened (searches, results, passes and photos opened, shares, errors, page speed), tied to a random ID that lives only as long as the browser tab, with the device class, your country (from Vercel's edge), the referring site, any UTM tags and the app version. |

Raw events and visits are deleted after 90 days. Daily usage totals, lookups and shares are kept.

Watched's database never stores exact coordinates, IP addresses, cookies or full referrer URLs, and the event relay never reads the IP. The app never sends street-level place names. Vercel and Supabase see IP addresses in transit and in their own request logs, like any host.

Other services see the place too. Photon sees what you type, or your coordinates if you use your location. Planetary Computer and NASA GIBS see the point and the area around it, to send the photos, and so does EUMETSAT where a Meteosat watches the place. Element 84 sees it only when Planetary Computer is down. Vercel Web Analytics receives the page address, which for a place link includes its coordinates and name.

Usage events are sent only from watched.earth, and never from a development build, an automated browser or a tab opened with ?noanalytics=1 (for as long as that tab stays open). The flag doesn't stop lookups and shares being counted: any build with Supabase configured counts them, development included. Vercel Web Analytics is cookieless and ignores the flag.

Run it locally

You need Node 22.12+, 24 or 26+, the versions Vitest supports.

git clone https://github.com/dev-Armaan/satellites.git
cd satellites
npm install
npm run dev

The app runs at http://localhost:5173 with no configuration. Without a backend nothing is recorded, the places-checked counter on the landing page is hidden, and share links carry the pass in the URL instead of a short /s/ link.

To turn on lookups and shares:

1. Create a Supabase project and apply the migrations, as docs/SELF-HOSTING.md shows.
2. Copy .env.example to .env.local and set VITE_SUPABASE_URL and VITE_SUPABASE_PUBLISHABLE_KEY. Use the

1. Run npm run dev as before, or npx vercel dev to serve the share pages and cards in api/ as well. Vercel asks

The places-checked counter appears once a project has 1,000 lookups, 50 of them in the last 24 hours.

Tests and scripts

npm test                    # engine, imagery and UI tests (Vitest)
npm run test:backend        # tests for the api/ functions
npm run typecheck           # tsc -b
npm run build               # the app and the /admin page, into dist/
npm run data:celestrak      # refresh the orbit catalog (CelesTrak asks for 2 hours between downloads)
npm run textures -- ./maps  # rebuild public/textures from the source maps in ./maps
render share cards for sample passes to image files (needs no server or database)
npx tsx scripts/backend-render-og.ts

The built textures are committed, so you rarely need npm run textures. It needs Python 3 and Pillow, and reads the source maps listed at the top of scripts/build-textures.py.

Useful URLs

| URL | What it does | |:--|:--| | /?q=lat,lon&n=name | Opens a place directly. Add &p= to open a pass. | | /?debug=gl | WebGL diagnostics. | | /?sandbox= | Development pages (dev server only): engine, backend, globe, imagery, results, shell. | | /admin.html?mock=1 | The stats page with fixture data (dev server only). |

Self-hosting

Watched is a static Vite build, three Vercel functions, an optional Supabase project and a GitHub Action that keeps the orbit catalog fresh. To run your own copy:

1. Fork the repository and import it into Vercel. It works as is, with no backend.
2. Enable GitHub Actions on your fork so the catalog refresh runs. Forks start with scheduled workflows off.
3. For lookups, shares and stats, apply supabase/migrations to your own Supabase project (they need pg_cron), set

1. For usage events, add your domain to PRODUCTION_HOSTS in src/lib/telemetry.ts. A fork sends none until you do.

Project layout

index.html            app shell and static boot screen
admin.html            /admin stats page (separate build: vite.admin.config.ts)
vercel.json           functions, headers, /s/:id and bot-unfurl routes, SPA fallback
src/
  main.tsx            entry; analytics and in-app events after first paint (production only)
  types.ts            shared contracts
  app/                phase controller, boot curtain, error notice, telemetry wiring
  engine/             catalog, satellite profiles, SGP4, pass search and worker pool, matching,
                      weather and geostationary legs, GPU elements, the report
  imagery/            STAC and GIBS, crop and mask URLs, pixels worker, cloud at your spot, Photon, time zones
  globe/              three.js / React Three Fiber scene: Earth, atmosphere, clouds, stars,
                      GPU satellites, pass sequence, swath, camera
  ui/                 system primitives, HUD, landing, results, share, About
  lib/                geo maths, backend client, telemetry, layout
  state/              zustand store and scene clock
  styles/             tokens, fonts, base
  admin/              /admin page (Supabase Auth)
  sandbox/            development-only ?sandbox= pages
api/                  og.tsx (share card), s.ts (share page), e.ts (events relay), _lib, _fonts, _assets
public/               data/ (orbit catalog), textures/, brand/, og-default.png
supabase/             migrations 0001 to 0007, SQL tests
scripts/              catalog fetch, textures, fonts, card render, migrate, admin, verify, SQL test, purge
docs/                 DESIGN.md, ARCHITECTURE.md, SELF-HOSTING.md
.github/workflows/    catalog.yml (orbit catalog refresh)

Data and credits

| Source | Credit | |:--|:--| | Orbits | Element sets from CelesTrak, based on US Space Force tracking data, refreshed every 6 hours. SGP4 by satellite.js. | | Sentinel‑2 | Contains modified Copernicus Sentinel data, followed by the year each photo was taken. | | Landsat | Landsat imagery courtesy of the U.S. Geological Survey and NASA. | | NASA GIBS | Imagery from NASA's GIBS, part of EOSDIS. GOES via NOAA and CIRA, Himawari via JMA. | | Meteosat | Contains modified EUMETSAT Meteosat data, followed by the year, from EUMETSAT's map service. | | Archives | Microsoft Planetary Computer and Element 84 Earth Search; Landsat's 15 m band from the Copernicus Data Space Ecosystem. | | Places | Photon by komoot. Map data © OpenStreetMap contributors (ODbL). | | Textures | Solar System Scope (CC BY 4.0), from NASA Blue Marble and Black Marble, partly by way of the three.js examples. Resized, re-encoded and repacked for this project. | | Fonts | Instrument Sans and Serif by Instrument, Martian Mono by Evil Martians (SIL OFL 1.1). |

The screenshots in this README and the default share image contain modified Copernicus Sentinel data 2026. Licenses and attribution for every bundled asset are in THIRD_PARTY_NOTICES.md.

Contributing, security and license

Issues and pull requests are welcome; CONTRIBUTING.md lists the checks to run first. Please report security issues privately, as SECURITY.md describes, and not in a public issue.

The code is released under the MIT License, © 2026 Armaan Gupta. Imagery, orbital data, textures and fonts keep their own terms, listed above. The Watched name and wordmark identify the official site at www.watched.earth, so please don't present a fork as the official site.

_{Made by Armaan Gupta · @armaangupt0 on X}