Sorry That's Not A Meteor, It's A Satellite
A day doesn’t seem to go by without an image popping up in my social media feed of someone proclaiming proudly that they’ve captured a meteor only to be sharing an image of a satellite or plane trail. It’s an easy mistake to make, even the mainstream media has a habit of using images of satellites and star trails when writing about meteor showers. So rather than simply bursting their bubbles with a brash comment, I thought I’d make this article to help educate others about how to identify what it is you’ve captured.
Aircraft trails have dotted lines from blinking navigation lights.
Aircraft trails are easy to identify as the blinking navigational lights on the wings and tails cause dotted patterns alongside the solid lines from any lights that are constantly on. If the aircraft is low on the horizon, it is likely to be further away from you and so the dots will be more densely packed and it will take much longer for the plane to travel across your frame compared to those that are higher in the sky or overhead.
Aircraft are easily identified as the blinking navigational lights cause a dotted pattern, alongside a trail for any lights that are on constantly.
Both meteors and satellites have tapered ends.
This is likely where most of the confusion comes from, as people see the fading streak and assume it’s a meteor.
In the case of a meteor, the tapered end comes from the meteoroid slowly starting to brighten as it enters Earth’s atmosphere and begins to heat up through friction. For a satellite, it may be that it is passing into, or out of, Earth’s shadow or that the satellite is flaring as the incident angle between you, it, and the Sun, slowly becomes favourable to reflect the light in your direction.
But the way they taper can differ.
Meteors typically have one long tapered end as they begin to heat up and brighten slowly and then they taper off very quickly, sometimes with a few instantaneous bursts in brightness as the meteoroid finally burns up. Sometimes they even explode in emphatic fashion, creating a bulge of light at the end of the trail.
Meteors showing one long tapered end as they begin to heat up slowly, followed by a quick drop in brightness. You can also see great fluctuations in the brightness at the end of the trail as the meteorite completely burns up or explodes.
Satellites fade as they enter Earth’s shadow.
Unlike meteors, satellites don’t give off their own light, they reflect the Sun’s light. So as they slowly pass into the shadow that is cast by Earth into outer space, they fade slowly and taper off. You can see this quite easily with the naked eye by watching the International Space Station pass over. It will eventually fade into the darkness and sometimes you can even see it turn red as it enters the sunset light.
The International Space Station slowly fading as it passes into Earth’s shadow.
More Satellites are visible in the twilight hours
As they are reflecting the sun’s light, more satellites are visble in the hours after sunset and before sunrise. Once the Sun is far enough below the horizon, any satellites overhead will be in darkness and thus, not visible. This is bad news for those who live at high latitudes as during summer there is a perpetual twilight, the Sun doesn’t make it very far below the horizon, so satellites will be streaking across the sky all night. Even here in the UK we have a perpetual astronomical twilight during June and July.
It’s worth noting that geosynchronous satellites sit at an altitude of 35,000km and are perpetually bathed in sunlight but they are so far away that they only appear as a small star in your images (more on those at the end of the article).
Satellites can flare
Have you ever been driving along the motorway on a sunny day when all of a sudden the Sun’s light is blindingly reflected from a house window as you drive past it? A similar thing happens with satellites as they pass overhead. At some point, the incident angle between you, it, and the Sun, becomes favourable to reflect the light directly into your line of sight. But this doesn’t happen instantaneously, it happens gradually, thus giving tapered ends either side of the flare. The tapered ends from a satellite flare are normally far more even, symmetrical and uniform compared to meteors.
Perhaps the most well-known are Iridium flares. This array of 66 satellites provides a global satellite communications network. The original satellites had a highly reflective door-sized antenna that would focus sunlight on a small area of Earth’s surface, causing a bright flare to appear in the night sky. The original satellites have now been replaced with second-generation satellites that don’t flare, although there are still a few of the original satellites lingering up there slowly de-orbiting or tumbling out of control.
Satellite flares are often mistaken as meteors, but the bulge in brightness is much more even and symmetrical compared to meteors.
Satellites often appear in consecutive frames.
Some satellites flare a lot more slowly, gradually increasing and decreasing in brightness. Sometimes when only part of the satellite trail is captured in a single exposure it often leads to a trail that mimics that of a meteor, with one long tapered end and one short tapered end.
As meteors burn up very quickly (typically less than a second but sometimes a few seconds) then it is very rare to capture them in consecutive exposures. Satellites, on the other hand, travel across the sky much more slowly and may be seen in several consecutive exposures.
The image to the left could easily be mistaken for a meteor, however, the trail was also present in the exposures before and after. The image to the right shows the three exposures blended together. There’s simply no way a meteor can travel across the sky that slowly for 60 seconds!
If you capture a uniform line, then you have likely captured part of a satellite trail. They’ll typically be white, or white-blue.
You can identify which satellite you’ve caught using Heavens Above
You can identify which satellite you’ve caught with the Heavens Above app.
At the time of writing, it’s only available for Android and their website only allows you to scour the archive for the current year. The app, however, allows you to check any date in the past, present or future, although the further ahead in time you look the less accurate the prediction.
If anybody knows of a similar app for iOS or a website that allows you to look further back in time, please let me know in the comments below. You can have some luck by checking Stellarium but I find it’s not as accurate as Heavens Above.
The International Space Station, currently the brightest satellite with sightings typically lasting a few minutes. Elan Valley, Wales
StarLink satellites appearing in a train a few days after launch. Brecon Beacons, Wales
Tumbling Satellites
Also keep an eye out for tumbling satellites. These are satellites that are spinning out of control, some of them are discarded rocket bodies and others are just malfunctioning satellites. As they are spinning out of control they flash periodically, blinking as they cross the sky. You can spot one entering from the top-right of the frame in the timelapse below:
Meteors have colour
One of the biggest tell-tale signs is that meteors have colour, whereas satellite trails are white or white-blue. Some caution has to be taken in using this alone to distinguish between the two as some lenses may suffer from heavy chromatic aberration (colour-fringing) which could make the trail appear to have colour. Also, depending on the ISO setting used to capture the meteor, the highlights may blow-out and the colour information lost, but you still should be able to see some colour in the fainter section of the trail.
The colour of a meteor depends on the chemical composition of the meteorite.
Perseid meteors are famous for their half-pink and half-green trails, caused by the high concentrations of calcium and magnesium in the meteorites.
A Lyrid meteor captured from my garden during the Covid-19 lockdown. Notice that it has a red tinge to it. It’s also pretty clear from the uneven brightening that it’s a meteor, as well as the fact it points back towards the constellation Lyra, where the radiant point lies.
Meteors from a meteor shower can be followed back to a radiant point
If there is an active meteor shower, a sure-fire way to confirm that it’s a meteor is to trace a line backwards from the trail. It should point towards the radiant point. The radiant point is what gives meteor showers their name. The Geminids meteor shower has its radiant point in the constellation Gemini, the Perseids in Perseus, the Lyrids in Lyra and so on. It’s worth noting that you don’t have to be facing the radiant point to see the meteors, they will fall all over the sky.
The Geminids meteor shower has its radiant point within the constellation Gemini. Image taken in La Palma, 2018.
The Perseids meteor shower has its radiant in the constellation Perseus. Image taken at Durdle Door, England, 2016
Large meteors leave vapour trails
Particularly bright meteors are known as bolides or fireballs. The name is given to meteors that are brighter than Venus in apparent magnitude (Venus at maximum brightness is around -4.5 magnitude). Bolide meteors can sometimes leave behind vapour trails which can be seen in the frames of a timelapse following the meteor.
Notice the vapour trail that looks like smoke left behind in the wake of the meteor.
Check out some meteors captured in real-time video in my Astro Vlogs below:
Summary
So to wrap it all up I’ve highlighted the main points below. Sometimes it’s never 100% clear cut, but over time you’ll be able to spot the difference easily.
Meteors
Have one long tapered end
Can show fluctuations in brightness and bulges where the meteorite burns up and explodes
Typically have colour
Can be traced back to a radiant point during meteor showers
Very rarely caught in consecutive frames
Satellites
Can have tapered ends but usually more uniform compared to meteors
White or white-blue in colour
Can flare and cause a bulge in brightness, more symmetrical than meteor burn up
Often appear in consecutive frames
Can be predicted and identified using Heavens Above
BONUS: Geosynchronous Satellites (GEOstationary Satellites)
Some satellites are geosynchronous, meaning they maintain a constant position above Earth. They’re difficult to ‘accidentally’ capture as in a normal exposure they will just appear like any other star, however, if you take an exposure long enough for star trails then they stand out a bit better. Find out how to photograph them here.