When to see the ISS in Tromsø

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Every time on this page is now worked out in Tromsø, in local time. Pick another city and the page recalculates the times, heights and visibility for it.

Visible passes in Tromsø

The ISS will not cross a dark sky in Tromsø over the next 10 days. This happens several times a year: the station flies over in daylight or inside Earth's shadow, where it cannot be seen. The next viewing window opens in a few days or weeks; this page updates every day.

How to see the ISS

The ISS is the brightest artificial object in the night sky, often brighter than any star. You need no binoculars or telescope, only the time and the direction. A few minutes before the pass, stand where you have an open view towards the side the station will come from.

It looks like a bright, steady point that glides silently across the sky in a few minutes. It does not blink and has no coloured lights, which is how you tell it from a plane. A pass lasts one to six minutes. Sometimes the station fades out before it reaches the horizon: it has flown into Earth's shadow and sunlight no longer reaches it.

Why only in the evening and morning

The ISS has no light of its own; we see sunlight reflected off it. So two things must happen at once: the observer's sky has to be dark, and the station, 400 km up, still has to be in sunlight. That is the case in the first hours after sunset and the last hours before sunrise.

Around midnight the station is usually in Earth's shadow. In summer at northern latitudes the Sun does not sink far below the horizon, so a sunlit station can sometimes be seen all night; in winter the windows are shorter. Because the orbit is tilted by 51.6°, the viewing periods shift every few weeks: for a while the station shows in the evenings, then in the mornings, with a few days without visible passes in between.

How to read the brightness

Brightness is given in magnitudes: the lower (more negative) the number, the brighter. The brightest stars are around 0, Jupiter about −2, Venus about −4. The ISS is brightest when it passes nearly overhead with the Sun behind the observer, and can reach −3.5 or more.

The brightness on this page is an estimate from the distance to the station and the lighting angle. Against Heavens-Above, the times agree to the minute and the heights to a degree, the brightness to about half a magnitude.

How to photograph it

A phone on a tripod in night or manual mode is enough. Set an exposure of 10–30 seconds and start shooting as the station appears: it becomes a bright streak across the stars. Several frames in a row, stacked on a computer, show the whole arc from horizon to horizon.

Where the ISS is now

At 20:57 the station is over 1.7° N, 133.8° E, 422 km up, moving at 7.66 km/s. It starts its next orbit in about an hour and a half, and every track over the ground shifts about 23° west, because Earth turns underneath it in the meantime.

About the station

The International Space Station is a joint project of the United States, Russia, Europe, Japan and Canada. Its first module, Zarya, was launched on 20 November 1998, and people have lived on board without a break since 2 November 2000. Usually around seven astronauts work there, running experiments in weightlessness.

The station is 109 m long, about the size of a football pitch, and weighs around 420 tonnes. It orbits Earth roughly every 90 minutes, so the crew sees about 16 sunrises and sunsets a day. NASA plans to operate it until 2030 and to bring it down safely over the ocean in early 2031.

How it is calculated

The station's orbit is the CelesTrak two-line element set (TLE), refreshed once a day (the current one is from today). The position is computed every 20 seconds with the SGP4 model, the same model NORAD orbit data are made for. A pass counts as visible when the station is more than 10° high and lit by the Sun, and the Sun is more than 6° below the observer's horizon.