Is that a UFO or a Starlink train? How to tell

If you have seen a line of lights crawling across the sky like beads on a string, you are in very good company. Since SpaceX began launching its Starlink satellites in batches, these "trains" have become one of the most common reasons people search for "UFO" late in the evening. The good news is that a Starlink train is one of the easiest sightings to confirm.

What a Starlink train is

Starlink is a large constellation of internet satellites operated by SpaceX. The first full batch was launched in May 2019, and launches have continued frequently since.

Satellites go up in groups on a single rocket. For a while after launch, they travel close together in a low orbit, one behind another, before gradually raising themselves and spreading out. During that early period, if the sunlight catches them, you see a straight line of points moving together.

Why only at certain times? A satellite has no lights of its own. You see it because it reflects sunlight. Around dusk and dawn, the ground where you stand is in darkness while the satellites high overhead are still in sunshine. Later in the night, they pass into Earth's shadow and disappear.

The five-point check

Feature	Starlink train	Aircraft	Something to report
Arrangement	Evenly spaced points in a straight line	Single object, or a few in loose formation	Anything that doesn't fit either
Lights	Steady, white, no color	Blinking strobe; red light on the left wingtip, green on the right	Pulsing or color changes not caused by twinkling
Sound	None	Usually audible if low enough	None, at low apparent altitude
Motion	Smooth, constant speed, straight path	Steady, can turn or bank	Sudden stops, reversals, sharp turns
Disappearance	Points fade one by one in roughly the same spot	Flies out of sight	Abrupt vanishing in open sky, not at a horizon

If your sighting matches the left column on all five, you very probably saw a satellite train.

How to confirm it in two minutes

1. Note the time and direction. Which way was the line traveling? Most trains move roughly west to east, though the angle varies.
2. Check the time against sunset or sunrise. Trains are typically visible within a couple of hours of either.
3. Look up recent launches. A train is brightest and most tightly grouped in the days just after a launch.
4. Use a satellite-tracking tool. Free websites and phone apps, such as Heavens-Above, show predicted satellite passes for your location. Enter your position and the time, and see whether a pass matches.

If the predicted pass lines up with what you saw, you have your answer.

Why satellites fade the way they do

One detail confuses many observers: the lights seem to vanish in midair, one after another, in the same patch of sky. That is the satellites entering Earth's shadow. Each one crosses the shadow line at the same place, so they blink out in sequence. It is one of the most distinctive things about a satellite train, and once you know it you will recognize it immediately.

Satellites that are not in a train

Starlink trains get the attention, but on any clear evening you can usually see individual satellites too. A single steady point of light moving smoothly across the sky over a few minutes, with no blinking, is very likely a satellite. The International Space Station is the brightest of them and is easy to spot when it passes; NASA's Spot the Station service will tell you when.

Some satellites also produce brief glints: a point that brightens for a few seconds and then fades as a flat surface catches the Sun. These can look startling, especially if you were not looking at the right spot until the flash.

When it is not Starlink

Here is the honest part. Satellite trains explain a lot of reports, but not all of them. A sighting deserves a second look if:

• The lights were not in a straight line or changed spacing.
• They changed direction or stopped.
• They were seen in the middle of the night, when satellites at low orbit would be in shadow.
• They were below clouds. Satellites are hundreds of miles up, so they are always above any cloud.

Those observations do not mean you saw something extraordinary. Aircraft formations, drones and balloons are next on the list. But they mean the satellite explanation does not fit, and your notes become more useful.

Why this matters

Every misidentified satellite that ends up in a report adds noise. NASA's 2023 independent study panel said the biggest obstacle to understanding UAP is poor data. Ruling out satellites quickly, and saying so in your notes, is one of the most useful things a skywatcher can do. The sightings that remain after that check are the ones worth a closer look.