Reading the night sky: satellites, meteors and flares

The night sky looks still, but it is busy. On a clear evening away from city lights you might see a dozen satellites, a few meteors, an aircraft or two and, on a lucky night, something stranger. The trick to reading it is not knowing every object. It's knowing the speed and shape of each kind of light.

The time test

The single most useful observation you can make is how long a light was visible. That alone sorts most sightings.

How long it lasts	What it probably is
A fraction of a second to a couple of seconds	A meteor
Several seconds, very bright, maybe with fragments	A fireball, an unusually bright meteor
A few seconds of brightening and fading in one spot	A satellite glint
A few minutes, crossing smoothly from one side of the sky to the other	A satellite or the International Space Station
Several minutes, slowly descending and fading	A parachute flare, if near a military range
Many minutes, a glowing expanding cloud at twilight	A rocket launch plume
Hours, barely moving	A planet or star

Satellites

A satellite looks like a steady star gliding across the sky. It takes a few minutes to cross, makes no sound, and does not blink. Satellites shine by reflected sunlight, so they're easiest to see in the couple of hours after sunset and before sunrise, when the sky is dark but they are still in sunshine.

The International Space Station

The ISS is the brightest satellite. It orbits Earth roughly every 90 minutes (per NASA), so it can pass over the same area more than once in an evening. NASA's free Spot the Station service gives pass times for your location. Seeing it pass on schedule is one of the easiest and most satisfying things to do with a clear sky.

Satellite trains and glints

Newly launched groups of satellites can appear as a line of lights moving together; our file on Starlink trains covers them in detail. Individual satellites can also flash briefly as a flat surface catches the Sun.

A note on Iridium flares. Older guides describe "Iridium flares," brilliant flashes from the first-generation Iridium communications satellites. Those satellites were retired and brought down by the end of 2019, so those famously predictable flares are now history. Glints from other satellites still occur, but less predictably.

Meteors and fireballs

A meteor is a small piece of space debris burning up as it enters the atmosphere. It lasts a second or two and moves fast, often leaving a brief trail.

A fireball is a particularly bright meteor. The American Meteor Society describes a fireball as a meteor brighter than the planet Venus. Fireballs can break apart, change color, and occasionally produce a sonic boom minutes later. Because they are bright, sudden and sometimes appear to fall nearby, they are a common source of startling reports. They are almost always much farther away than they look.

Meteor showers

At certain times of year Earth passes through trails of debris, and meteors become more frequent:

• Quadrantids: early January
• Perseids: peaking around mid-August
• Leonids: mid-November
• Geminids: peaking around mid-December

On a shower night, a run of bright streaks is expected, not mysterious.

Rocket launches

Rocket launches at twilight can create spectacular glowing plumes high in the atmosphere, still in sunlight while the ground below is dark. The exhaust spreads into strange shapes, sometimes a glowing spiral or jellyfish-like cloud, and can be seen hundreds of miles from the launch site. If you see a sudden glowing cloud expanding at dusk or dawn, check whether there was a launch that evening.

Flares

Military illumination flares descend slowly under parachutes and burn brightly for several minutes, often in a row. They're dropped during training over military ranges. The second event of the 1997 Phoenix Lights was attributed to flares of this type. If you live within sight of a range, flares should be on your list.

Aircraft

Aircraft have navigation lights: red on the left wingtip, green on the right, and white at the tail, plus flashing strobes. Head-on, an airliner's landing lights can look like a single brilliant, motionless light for a long time, especially on approach to an airport. Free flight-tracking apps will show what is in the air near you.

Building the habit

1. Look for duration first. It narrows the options more than any other detail.
2. Note the direction of travel. Many satellites move west to east or roughly north–south.
3. Check the calendar. Showers, launches and ISS passes are all predictable.
4. Keep a simple log. Time, direction, duration, appearance. Over a few months you'll start recognizing patterns.

Once you can read the regular traffic, the truly unusual stands out, and you will be able to describe it in a way that makes it worth investigating.