Revelers at this year’s Seafair Summer Fourth will see something different in the sky above Lake Union Friday: Humans.

Twice during the evening festivities, skydivers will parachute over the lake, the second time equipped with large sparklers firing from their feet. “It will look like comets streaking across the sky,” said Pete Moran of Seattle’s Rezin Marketing.

That second jump, by Shelton skydivers Luke Aikins and Andy Farrington, is set for 10:10 p.m., with the skydivers to land in the lake shortly before the fireworks show begins.

That’s not the only new twist for the celebration this year.

To its traditional Gas Works Park home, the event is adding Lake Union Park on the lake’s south shore. Both venues will feature live entertainment, food vendors, beer gardens, visits by Seafair clowns and pirates, and other activities.

Lake Union Park has been a popular spot for fireworks-watchers in the past, but this will be the first time it will have the added Seafair attractions.

Gates open at noon at both parks. Admission is free, except for reserved seats in viewing stands, which were nearly sold out by Thursday afternoon.

Around Puget Sound, parades, games, concerts and other Independence Day festivities are planned. Other cities hosting fireworks include Bellevue, Tacoma, Edmonds, Renton and Kirkland. (For an expanded list, see today’s Weekend Plus section.)

At Lake Union, the 20-minute choreographed fireworks show will be put on by Western Display Fireworks, a five-generation, Oregon-based company that will conduct more than 200 fireworks shows around the Northwest this weekend.

Reporters who visited the 280-foot barge Thursday, from which thousands of shells will be launched above Lake Union, heard company owner Bob Gobet admit he really doesn’t enjoy a fireworks show when it’s happening: too many details, too many things to worry about.

His enjoyment, he said, comes afterward, “when I get a chance to see the video.”

Workers on the barge have been setting round shells, the largest 10 inches in diameter, into steel tubes anchored in sand.

Boxes on the barge deck showed the colorful names of some of the mostly Chinese-made fireworks: three-layer star mines, purple go-getters and orange spider chrysanthemums.

Although the number of shells is about the same as last year, Gobet said the barge is longer, allowing him to spread out the firing points in a way he hopes will make the display look larger.

Shells will be fired as high as 1,200 feet, and spread their colorful displays between 800 and 1,000 feet across, said Gobet, who’ll be in a plywood shelter on the barge during the show.

Gobet’s daughter, Heather, who designed the display, said the show is organized into segments, like the chapters of a book, with music and fireworks working together and building toward a spectacular finale.

State-of-the-art electronics, she said, enable her to time the explosions down to within 1/100th of a second.

Moran said the first skydiving jump is scheduled for 7:30 p.m., featuring four Skydive Kapowsin divers with devices that emit white smoke attached to their feet. They are to land at Gas Works Park.

Two of those four sky divers, Aikins and Farrington, will make the second jump, in which they’ll wear wingsuits that give them greater control of their flight for what Moran expects to be a dramatic visual effect.

On that second jump, the skydivers will leave the aircraft at 7,000 feet, and could be in the air for as long as five minutes, Moran said.

After the skydivers land, a Washington National Guard Chinook helicopter is to pass over the lake, towing a large American flag. Then the fireworks begin.

After several years of uncertainty over who would organize and pay for Seattle’s Independence Day fireworks show, Seafair is in the second year of a three-year agreement with multiple sponsors for the fireworks extravaganza, expected to cost more than $300,000.

Melissa Jurcan, Seafair spokeswoman, said major participation for the event comes from Amazon, Microsoft, DoubleDown Interactive and the Washington National Guard.

Jack Broom: jbroom@seattletimes.com or 206-464-2222