At least eight times a year, Coast Guard crews stationed at Bodega Bay launch their 47-foot lifeboat and an air crew takes flight in a Jayhawk helicopter from San Francisco to chase reports of a possible boat in distress.

The resource-intensive searches start with a call reporting a light in the sky — it could be a shooting star, a lit paper lantern or a distress flare shot from a boater in trouble somewhere on the Sonoma Coast's treacherous seas. They must assume the worst.

The details callers give can help save precious time for searchers trying to rescue people in seas that hover around an inhospitable 50 degrees year-round. Bad information can also launch a wild goose chase.

"The accuracy of information is critical," Petty Officer Second Class Ross Ellis with Coast Guard Bodega Bay said. "The ocean is a huge space and to try to communicate where they saw a flare is difficult."

On Friday night, Coast Guard Bodega Bay staff will be stationed at designated pullouts along the coast north of Jenner to help coastal residents, frequent boaters and others learn how to best describe the location and characteristics of lights in the sky.

A boat stationed off shore will shoot multiple kinds of flares, from commercial models to search flares used by the Coast Guard, as a demonstration.

"Did they see it rise and fall or just rise or just fall?" Ellis said. "Those two pieces of information can help us a lot."

Since September, the Coast Guard has launched at least three full-scale searches for flare reports off the Sonoma Coast. All have been suspended without finding anyone in trouble.

On Sept. 27, a caller reported seeing a flare somewhere off Tomales Bay and Dillon Beach. A boat and a helicopter began a grid search of the area that lasted until 1 a.m., Boatswain Mate Third Class Erik Dahl said.

The helicopter returned and searched again at first light but found nothing. The Coast Guard confirmed that no overdue vessels were reported in the area and the search was suspended.

"We don't stop until we saturate the area pretty well," Dahl said. "We'd rather go out and be sent home than miss a report."

Certain details — from color and size, how a light moves and how far above the horizon — can shape a search's success, he said.

Hold a fist up as if you're holding a cup of coffee with the pinky on the horizon. Use knuckles and additional fists to estimate the distance from the horizon.

"If it's only three knuckles off the horizon it's pretty far off shore," Dahl said.

Count the seconds until the flare disappears. Note the color of the light and how it moves, as if it's floating or sinking, and whether it rises and fals.

"Most of our calls are from people who live out at the coast; those people are our best eyes," Ellis said. "They are always looking out the windows, we rely on those people."

The flare demonstration will be held promptly at 6 p.m. Friday. Coast Guard staff will be posted at three pullouts along Highway 1 immediately north of Jenner near the mouth of the Russian River. For more information, contact Coast Guard Bodega Bay at 875-3596.

You can reach Staff Writer Julie Johnson at 521-5220 or julie.johnson@pressdemocrat.com. On Twitter @jjpressdem.