NASA astronaut Jessica Meir shared this photograph of the Lyrid meteor shower as seen from the International Space Station (ISS). Her view was a bit different then ours — she saw the Lyrids streaking through Earth’s atmosphere from above.
The Lyrid meteors are pieces of debris trailing comet C/1861 G1 Thatcher. This debris is spread non-uniformly in its orbit around the Sun, so every meteor shower is different. Lyrids can produce up to 15 to 20 meteors per hour. From the ground, they appear to be coming from the constellation Lyra (hence their name).
I would have loved to see a video instead, but the photo is still pretty cool. Video would have shown the dynamics of the shower. The streaks you see in the image only last a few seconds, and are then replaced by other streaks in different locations. And the changing pattern of streaks extends over a much large area than the photo shows. Doesn’t help that parts of the ISS got in the way. If you follow NASA’s live ISS camera feed during a meteor shower, you just might get lucky and see what I described.
Meir’s photo is a stunning visual reminder that our planet is protected by a relatively shallow atmosphere — its thickness is roughly 2% of Earth’s diameter. As Meir shared in her post, you can see how short the streaks are, and meteors only glow when they’re in the atmosphere.
Meteoroids hit the atmosphere with speeds ranging from 25,000 to 160,000 mph (40,200 to 257,500 km/h), with the Lyrids averaging 105,40 mph (169,200 km/h). At that speed, the time spent traversing the roughly 150 miles of atmosphere (and the time they glow) will be mere seconds.
The speed of the meteors depends on where Earth intercepts the debris swarm responsible for the shower. Earth’s speed in its orbit is fairly constant. It circles the Sun with an average speed of 66,000 mph (107,200 km/h). The debris swarm has its own speed in its orbit around the Sun, and that can add to or subtract from the Earth’s speed, depending on the geometry of the orbits.
The diagram below shows how meteor showers are more Earth running into the debris swarm, rather than the swarm targeting Earth. That swarm could be moving in any direction relative to Earth. It also shows why meteors are best seen in the hours before dawn — when the swarm is nearly overhead:
The view from the ground is quite different. Even though the meteors are coming in on roughly parallel trajectories, they appear to be diverging from a fixed point in the sky called the radiant. This is a result of the vanishing point effect commonly used to create the illusion of “depth” in 2D illustrations. But it happens in the real world anytime the parallel entities extend to a great enough distance, as with cloud streets. This is a time lapse photo of the Perseid meteor shower, so-named because its radiant is in the constellation Perseus:
Meteors light up as soon as they hit Earth’s atmosphere. When you see a meteor, you’re usually looking at a grain of dust burning bright about 50 to 75 miles (80 to 120 km) above ground. They usually disintegrate at altitudes of 31 to 59 miles (50 to 95 km). The exact altitude at which a meteor begins to glow, and at which it disintegrates, depends on its arrival speed and angle.
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