Night sky

What's overhead tonight?

When the International Space Station and China's Tiangong cross the sky over your postcode in the coming week, with where to look, plus tonight's sunset, twilight and dawn and the phase of the Moon.

  • Space station passes
  • Sunset, dusk & dawn
  • Moon phase

How this works

The two crewed space stations are the easiest satellites to spot: the ISS is brighter than any star, and Tiangong is not far behind on a high pass. They are only visible when three things line up: the station is above your horizon, it is in sunlight, and you are in darkness. That happens for a few minutes after dusk and before dawn. The page fetches the stations’ current orbits from CelesTrak, no more than once every few hours as they ask, and everything else is computed in your browser: the orbit is propagated with the standard SGP4 model for the next seven days, each pass is checked against the Sun’s position for both you and the station, and the same Sun model gives sunset, the three twilights and sunrise for your postcode. The Moon’s phase is worked out from its 29.53-day cycle.

Sources

  • Orbital elements: CelesTrak (Dr T.S. Kelso), which publishes the US 18th Space Defense Squadron’s general perturbations data free of charge and refreshes it every two hours.
  • Propagation and geometry: satellite.js (MIT licence), running in the browser.
  • Postcodes: postcodes.io / ONS Postcode Directory (OGL v3).

For information only. Predictions are good to about a minute for a few days ahead and less certain further out.