Compared with other annual showers, the Lyrids puts on a moderate show. That’s because its source, Comet Thatcher, typically leaves behind less debris than other comets do as it orbits the sun.

Comets are often described as dirty snowballs. As they voyage through the solar system, they spew specks of ice and rock. The dusty trails linger in space long after the comet leaves, only to burn ephemerally when Earth passes through the stream, creating a meteor shower.

Comet Thatcher makes its journey around the sun roughly every 415 years. Its last trip was in 1861 and it will make its next rendezvous in 2276. According to Dr. Cooke, when we see a Lyrid shower, we are seeing debris that fell from the comet not during its 1861 orbit, but from its previous one, around 1446, or even an earlier one. “Because the comet’s orbit does not intersect Earth’s,” he said, “the debris must have time to drift away in order for us to run into it.”

Some of the sparks we see during a shower come from cosmic crumbs no bigger than a pebble. It’s not the size that determines how bright it will be, Dr. Cooke said. Rather, it’s the speed at which its particles pierces the sky. But, again, don’t expect to catch many shooting stars this week.