SKY · FIELD GUIDE
What's That Light Crossing the Sky? A Spotter's Guide
You're outside after dark and notice a single 'star' that's moving — sliding steadily across the sky, not blinking, making no sound. Within a minute it's gone. What did you just see? Almost certainly a satellite catching the sunlight. Here's how to tell which one, and how to catch the bright ones on purpose.
Look up on a clear evening and wait a few minutes. Sooner or later you'll catch one: a single point of light, as bright as a star or brighter, sliding steadily and silently across the sky. No flashing. No engine noise. Often it simply fades away halfway across. You've just watched a satellite — and once you know what you're looking at, you can start catching the good ones on purpose.
The first test: is it even a satellite?
The giveaway is steady, silent motion. A satellite is a fixed point of light that moves smoothly across the sky over two to five minutes. It never blinks, because it isn't carrying lights — it's a mirror, reflecting the Sun. An aircraft, by contrast, carries flashing red and green navigation lights, usually makes a sound, and doesn't abruptly disappear. If your moving light is a steady white dot with no flash and no sound, it's a satellite.
The other tell is the vanishing act. Satellites frequently fade out partway across the sky. That's not your eyes — the satellite has flown into Earth's shadow, and with no sunlight to reflect, it goes dark instantly.
Why dusk and dawn are the magic hours
A satellite is only visible when two things line up: your sky is dark, and the satellite, far overhead, is still bathed in sunlight. That overlap happens in the hour or two after sunset and before sunrise. Deep in the night, most satellites pass through Earth's shadow and you'll see nothing. This is why the bright-passes tracker weighs tonight's dark-sky window for your location — the timing is everything.
The bright ones, brightest first
The International Space Station is the headline act. As big as a football pitch and wrapped in reflective solar panels, a good ISS pass is unmistakable — a brilliant, steady point outshining every star, crossing the whole sky in about five minutes. If you only ever spot one satellite, make it this.
A Starlink train is the showstopper newcomer: a tidy line of evenly-spaced lights drifting in single file. It's a freshly-launched batch of Starlink satellites, still clustered together before they climb to their working orbits and spread out. Visible for a few weeks after each launch, best soon after dusk, it's the sight that most often makes people grab a phone and ask the internet what they just saw.
Tiangong, China's space station, is like a fainter ISS — a steady, fairly bright point crossing smoothly. And Hubble is one for sharp eyes from a dark site, never climbing high from most latitudes.
Catching them on purpose
You don't have to leave it to luck. Tell the tracker where you are and it works out, from live orbital data, the next times each bright object crosses your sky — the time, the direction it rises, how high it climbs and how long it stays up. Be outside a few minutes early, look toward the direction it rises, and let your eyes relax on the whole sky rather than one spot. When that silent, steady light appears and slides overhead, you'll know exactly what it is.
Frequently asked questions
How can I tell a satellite from an aircraft?
A satellite is a single steady point of light that doesn't blink and makes no sound. It glides smoothly across the sky in two to five minutes, then often fades out mid-sky as it passes into Earth's shadow. An aircraft has flashing red and green navigation lights, usually a sound, and doesn't suddenly vanish. If it's a steady white dot moving silently, it's a satellite (or the Space Station).
Why do satellites only appear around dusk and dawn?
A satellite shines only by reflecting sunlight. To see one, two things have to be true at once: your sky has to be dark, but the satellite — hundreds of kilometres up — still has to be in sunlight. That overlap happens in the hour or two after sunset and before sunrise. In the middle of the night most satellites pass through Earth's shadow and are invisible, which is why one will often fade out partway across the sky.
What's the brightest satellite I can see?
The International Space Station, by a wide margin. It's the size of a football field with huge reflective solar panels, so a good pass outshines every star and even the planets — a brilliant, fast, steady point crossing in about five minutes. Nothing else human-made comes close on a typical night.
What is the 'string of lights' I saw?
That's a Starlink train — a batch of newly-launched Starlink satellites still bunched together in a line before they spread out to their working orbits. For a few weeks after each launch they appear as a startling row of evenly-spaced lights drifting silently across the sky, best in the hour after dusk. It's the single most-asked 'what was that?' of recent years.
Do I need any equipment?
No. Every object in this guide — the Space Station, a Starlink train, the Tiangong station — is a naked-eye object on a good pass. Binoculars can help you pick out a fainter one like Hubble, but the bright passes are meant to be enjoyed with just your eyes. The only thing that matters is timing and a reasonably clear, dark sky.
How do I know when one will pass over me?
That's exactly what the bright-passes tracker does: tell it your location and it computes, from live orbital data, the next times each bright object crosses your sky — when to look, which direction it rises, how high it climbs and how long it's visible. The visible window shifts a little each night, so it's worth checking the day you want to look.
SEE IT LIVE
Everything in this guide is on the live sky map.