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Why do meteor shower rates vary from year to year?

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Meteor and meteoroid The Cabin Creek meteorite, an iron (nickel-iron alloy) meteorite that was observed to fall in northwestern Arkansas on March 27, 1886. Its characteristic pattern of “thumbprint” dimples, or regmaglypts, is the result of melting and consequent ablation of its surface as it traveled through the atmosphere. The meteorite is likely a fragment of one of the M class asteroids, which show significant nickel-iron in their surface material.

The primary reason meteor shower rates vary from year to year is that the density of meteoroids within meteor streams is not uniform. As Earth passes through these streams of debris left behind by comets, the number of observed meteors fluctuates based on the concentration of particles encountered along the orbit.123

In some cases, such as the Leonid meteor shower, meteoroids remain clustered in a compact swarm near the parent comet, leading to dramatic spikes in activity that recur at intervals corresponding to the comet's orbital period. Over thousands of years, gravitational perturbations and orbital dynamics disperse these particles more uniformly along the comet's path, which typically results in showers that are more consistent in strength but less intense.32