At any given moment, there are up to six humans orbiting 400km above our heads in a huge science laboratory. The International Space Station (ISS) is the Earth’s biggest artificial satellite, and it’s also a very good reflector of sunlight, making it the brightest object in our sky after the Sun and the Moon.
Spotting the ISS with the naked eye is one of the most fun and rewarding stargazing activities – you just need to know when and where to look. The ISS is travelling at a speed of around 28,000km/h (planes, by comparison, fly at around 900km/h), so it whizzes around the Earth once every 90 minutes, and crosses the sky in six minutes or less.
Sighting opportunities range from once a month to several times a week, depending on the path of the ISS’s orbit, and the time of year. During northern hemisphere summer, the ISS receives enough sunlight to make it visible at all times of the night. For the rest of the year, the ISS only gets enough light around sunrise or sunset (during the middle of the night, it is too dark against the sky).
To spot the ISS, look for a bright, white spot of light moving quickly across the sky. The light will be constant, so if it flashes, or you see red lights, that’s a plane.
To find out when the ISS will be visible near you, enter your location at NASA’s ‘Spot the Station’ website (spotthestation.nasa.gov). It’ll tell you exactly when the ISS will be overhead and in which direction to look.
You can also sign up to receive alerts around 12 hours before each sighting opportunity. If you live in an area with lots of buildings, look for sightings with a ‘max height’ of at least 40° – any lower and there’s a good chance that the ISS will be obscured.
Looking for stargazing tips? Check out our complete astronomy for beginners UK guide.