Why do meteor showers come back on the same nights every year?
Every August, Earth drives through the crumbs of a comet, and every August the crumbs are still there.
▶ Start the storyMeteor showers come back every year because they are made of a 's leftovers, and Earth drives through the same trail on the same date. Each time a comet swings by the Sun, some of its ice and a certain number of are shed. They spread out along the comet's whole path to form a stream, called a dust trail. Earth crosses the stream every year at much the same rate, so the shower is annual.
The shooting stars we see are tiny. Most meteors are smaller than a grain of sand, and almost all of them before they hit the ground. They enter the atmosphere at extremely high speeds, and the streak of light is the fragment burning up.
Why do the streaks seem to fan out from one spot? The particles travel on parallel paths, and by they seem to radiate from a single point, like parallel railroad tracks converging at the horizon. Showers are named after the constellation where that point lies. The Perseids, which peak on 12 August every year at over one meteor per minute, seem to come from Perseus.
Step 1: The passes the Sun
Some of its ice and sheds
Step 2: A dust trail forms
The debris spreads along the 's whole path
Step 3: Earth crosses the trail
At much the same time every year
Step 4: Shooting stars
Grains smaller than sand burn up in the atmosphere
It took a long time to understand any of this. For a long time meteors were regarded as an atmospheric phenomenon, until Ernst Chladni proposed in 1794 that they originated in outer space. In 1866 Giovanni Schiaparelli showed that a shower shared the orbit of a , and proposed that meteors come from comets. For the best view, wait until the point they seem to come from is well above the horizon: the rate is low when it is near the horizon, and at 30 degrees up it is at least half its maximum.
687 BCE
Earliest Chinese record of the Lyrids
1794
Chladni proposes that meteors come from outer space
1833
The great Leonid storm shows a cloud of space dust
1866
Schiaparelli ties meteors to comets
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Recap
Showers come back each year because Earth crosses the same comet's dust trail on the same date.
💡 A trick to remember it · A comet leaves a crumb trail; every year Earth drives over it, and the crumbs flash as shooting stars.
Surprising fact · A shower's streaks seem to fan out from one point only because of perspective, like railway tracks.
Sources (1)
No source, no claim. Every fact in this lesson (15 claims) cites at least one of these.